Thrombophilia pathophysiology: Difference between revisions

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==Overview==
==Overview==
The pathogenesis of thrombophilia is multi-factorial. It is characterized by hypercoagulability, which by itself or in synergy with '''endothelial injury''' or '''stasis''' ([[Virchow's_triad|Virchow's Triad]]) can predispose to [[thrombus|clot formation]]. Multiple [[Thrombophilia_classification|genetic mutations and predisposing conditions]] have been associated with the increased risk of [[thrombosis]] due to abnormalities in the [[coagulation]] cascade.<ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638  }} </ref> The most common genes involved in the pathogenesis of acquired thrombophilias are [[Factor V Leiden]] and '''[[prothrombin]] gene mutations'''.
The pathogenesis of thrombophilia is multi-factorial. It is characterized by hypercoagulability, which by itself or in synergy with '''endothelial injury''' or '''stasis''' ([[Virchow's_triad|Virchow's Triad]]) can predispose to [[thrombus|clot formation]]. Multiple [[Thrombophilia_classification|genetic mutations and predisposing conditions]] have been associated with the increased risk of [[thrombosis]] due to abnormalities in the [[coagulation]] cascade.<ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638  }} </ref> The most common genes involved in the pathogenesis of acquired thrombophilias are [[Factor V Leiden]] and '''[[prothrombin]] gene mutations'''.
*Coagulation is an inherent property of the hematologic system and under healthy conditions, normal blood flow is maintained by the balance between the pro-coagulant and anti-thrombotic factors. A hypercoagulable state and subsequent thromboembolism is a result of overactivity of pro-coagulant factors or a deficiency in anti-coagulants. The interplay of factors is complicated - coagulation activators and inhibitors and their production and degradation (quantitative) and functional properties (qualitative) all influence thrombosis. The triad of hypercoagulability, vascular stasis and vascular trauma as described by Virchow in 1856 still holds and remains the harbinger of vascular thrombosis. Arterial thrombosis results from atherosclerotic plaque rupture around which a platelet-rich white thrombus forms. Stasis behind venous valves contributes to venous thrombosis and red thrombus. Mutations influence coagulation depending on whether they are present in heterozygous or homozygous genotype.
*As noted, Virchow's triad (i.e., endothelial damage, hypercoagulability, & venous or arterial blood stasis) plays a significant role in the pathophysiology of thrombosis. Damage to the vessel wall leads to the production of pro-inflammatory (and prothrombotic) cytokines, an increase in available tissue factor, the proliferation of adhesion molecules, and enhanced platelet activation. Cytokines initiate inflammation-promoting interaction between leukocytes and endothelial cells. Inflammation is a normal body reaction to unwanted stimuli such as foreign pathogens or infection and endothelial damage, whether acute (e.g., trauma or surgery) or chronic (underlying inflammatory disorders or peripheral vascular disease). The activation of the leucocytes and endothelial cells causes the formation of adhesion molecules, which will eventually initiate clot formation. The body's endogenous anticoagulants, such as protein C & S and Antithrombin-III, prevent the formation of thrombosis through a complex regulatory mechanism that maintains homeostasis. When an imbalance exists in the formation and lysis of clot, it can generate thrombosis; this explains why patients with thrombophilias such as protein C, protein S, and antithrombin III deficiencies are prone to acquiring blood clots. As noted in the Etiology section, a myriad of additional acquired provoking risk factors and comorbidities (e.g., recent surgery, inflammation, infection, pregnancy, estrogen therapy, morbid obesity, or smoking, among others) also increase a chance of developing thrombosis.
*Thrombosis occurs throughout our arterial system, especially in those with predisposing cardiovascular risk factors. In the heart, microthrombi can develop as a result of blood stasis in the ventricles or atria due to underlying valvular heart disease, cardiomyopathies, or arrhythmias such as atrial fibrillation predisposing to ischemic emboli and CVA. Arterial thrombosis (and microthrombi formation) typically initiates by the accumulation of lipid plaques in the arterial wall, provoking chronic inflammatory cells and platelet activation, as can be seen with coronary artery disease. Platelets play a significant role in the development of arterial thrombosis compared to venous thrombosis, and this explains why antiplatelet agents form a cornerstone of the prevention and treatment of arterial thrombosis. The initial lipid plaques evolve into fibrous plaques. Fibrous plaques could rupture, and the erosion of the surfaces of some of these plaques could lead to the release of additional pro-coagulating factors. This process is called atherosclerosis. Atherosclerosis allows the activation of platelets, causing adhesion and aggregation, which leads to the formation of a clot. The occlusion of vessels due to atherosclerosis and thrombin formation in the coronary arteries of the heart may lead to ischemic heart disease and myocardial infarction.


==Pathophysiology==
==Pathophysiology==
* The primary mechanism for thrombus formation in common inherited thrombophilic states involves [[thrombin]] dysregulation.  
*Coagulation is an inherent property of the hematologic system and normal blood flow is maintained by the balance between the pro-coagulant and anti-thrombotic factors under healthy conditions. A hypercoagulable state and subsequent thromboembolism is a result of overactivity of pro-coagulant factors or a deficiency in anti-coagulants. Anticoagulants that regulate thrombin include [[antithrombin]], [[Protein_C|protein C]], and [[Protein_S|protein S]]. The primary mechanism for thrombus formation in common inherited thrombophilic states involves [[thrombin]] dysregulation. However, the interplay of these factors is complicated process consisting of coagulation activators and inhibitors and their production and degradation (quantitative) and functional properties (qualitative) influencing the thrombosis process.  
* Anticoagulants that regulate thrombin include [[antithrombin]], [[Protein_C|protein C]], and [[Protein_S|protein S]].
* Mutations in [[antithrombin]] can lead to increased thrombus formation.<ref name="pmid14347873">{{cite journal| author=EGEBERG O| title=INHERITED ANTITHROMBIN DEFICIENCY CAUSING THROMBOPHILIA. | journal=Thromb Diath Haemorrh | year= 1965 | volume= 13 | issue=  | pages= 516-30 | pmid=14347873 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14347873  }} </ref> 
* Protein C and S are natural anticoagulants which inhbit thrombin formation. Dysregulation in activated protein C (APC) can occur as either defects in the protein C or S molecule (Protein C and S deficiency) or as resistance to APC activity.<ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638  }} </ref> '''[[Activated protein C resistance|APC resistance]]''' occurs when APC fails to inactivate downstream coagulation factors, specifically [[Factor_V|Factor V]] and [[Factor_VIII|Factor VIII]].
* The most common inherited thrombophilia is [[Factor V Leiden]], which is a polymorphism of Factor V that is resistant to APC inactivation.<ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638  }} </ref> 
* The second most common inherited thrombophilia involves a gain of function mutation of the prothrombin gene ([https://en.wikipedia.org/wiki/Prothrombin_G20210A Prothrombin G20210A]) resulting in increased protein activity and thrombus formation.<ref name="pmid8916933">{{cite journal| author=Poort SR, Rosendaal FR, Reitsma PH, Bertina RM| title=A common genetic variation in the 3'-untranslated region of the prothrombin gene is associated with elevated plasma prothrombin levels and an increase in venous thrombosis. | journal=Blood | year= 1996 | volume= 88 | issue= 10 | pages= 3698-703 | pmid=8916933 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8916933  }} </ref>
* [[Familial_dysfibrinogenemia|Dysfibrinogenemia]] is a disorder of [[fibrinogen]] formation or activity resulting in predisposition for bleeding, thrombosis or both.<ref name="pmid11900586">{{cite journal| author=Cunningham MT, Brandt JT, Laposata M, Olson JD| title=Laboratory diagnosis of dysfibrinogenemia. | journal=Arch Pathol Lab Med | year= 2002 | volume= 126 | issue= 4 | pages= 499-505 | pmid=11900586 | doi=10.1043/0003-9985(2002)126<0499:LDOD>2.0.CO;2 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11900586  }} </ref>
 
 
[[Image: Thrombophilia_Path.jpg|thumb|center|500px|Thrombus formation in inherited thrombophilia. In thrombophilia, procoagulant and anticoagulant factors are dysregulated, leading to thrombus formation]]
 
'''Figure: Thrombus formation in inherited thrombophilias'''. Adapted from: N Engl J Med. 2001 Apr 19;344(16):1222-31.<ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638  }} </ref>
 
*'''Antithrombin III (ATIII) deficiency''': Antithrombin III binds to heparin on endothelial cells and forms a complex with thrombin (thrombin-antithrombin (TAT) complex) thus inhibiting coagulation. The prevalence may be 1 in 500 in the general population. Its deficiency may present as early age thrombosis (less than 50 years old) and carries the highest risk for thrombotic events among the inherited thrombophilias. Antithrombin is synthesized in the liver but is not vitamin K-dependent. ATIII deficiency can occur as a consequence of reduced synthesis (liver damage) or increased loss (nephrotic syndrome, enteropathy, DIC, sepsis, burn, trauma, microangiopathy, and cardiopulmonary bypass surgery). Qualitative defects of ATIII (type II deficiency) describe mutations which either affect the heparin-binding site (HBS), the reactive site (RS) or result in pleiotropic effects (PE). Homozygous ATIII deficiency is incompatible with life unless affecting the heparin-binding site. Usually these patients present with venous thrombosis and less likely with arterial thrombosis. Antithrombin (AT) deficiency is a heterogeneous disorder. AT It is usually inherited in an autosomal dominant fashion, thereby affecting both sexes equally.
Type I – The type I deficiency state results from reduced synthesis of biologically normal protease inhibitor molecules. In these cases both the antigenic and functional activity of AT in the blood are reduced. The values are reduced by approximately 50 percent in the heterozygote. The 1997 antithrombin mutation database included 80 distinct mutations in patients with type I deficiency. The database shows that the molecular basis for this disorder is usually a small deletion or insertion (less than 22 base pairs) or a deletion of a major segment of the AT gene.
Type II – Type II AT deficiency is produced by a discrete molecular defect within the protein. While the AT immunologic activity is normal in this deficiency, plasma AT functional activity is markedly reduced leading to risk of thrombosis.
Type III – This type is characterized by normal functional and antigenic antithrombin levels but impaired interaction between AT and heparin.


Affected patients have antithrombin levels 40–60% of normal, and 70% of those affected experience thrombo-embolic events before the age of 50. Thrombotic episodes are rare before puberty in AT-deficient individuals. They start to occur with some frequency after puberty, with the risk increasing substantially with advancing age.
[[Image: Thrombophilia_Path.jpg|thumb|center|500px|Thrombus formation in inherited thrombophilia. In thrombophilia, procoagulant and anticoagulant factors are dysregulated leading to thrombus formation]]


*'''Protein C deficiency:''' It present as thrombosis in teenagers. Protein C and S deficiency may be inherited but is also inducable by liver dysfunction, vitamin k antagonists, renal failure, DIC, and active thrombosis. Protein S enhances the effect of activated protein C. Protein S deficiency can be classified as type I (reduced quantity of protein S), type II (low APC activity), and type III (low free protein S due to increased binding to the complement factor C4b). The interaction of protein S with C4, which is an active phase reactant exemplifies the relation of coagulation, inflammation, and autoimmunity. The half-life of protein C is shorter than the half-life of other vitamin K-dependent coagulation factors, hence the risk of increased coagulation with the initiation of vitamin K antagonists and need for bridging with parenteral heparin (warfarin-induced skin necrosis).  
'''Figure 1: Thrombus formation in inherited thrombophilias'''. Adapted from: N Engl J Med. 2001 Apr 19;344(16):1222-31.<ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638}} </ref>
Protein C deficiency is a rare disorder, characterized by a reduction in the activity of protein C, a plasma serine protease involved in the regulation of blood coagulation. The active form of protein C, activated protein C (APC), exerts potent anticoagulant activity. A deficiency in protein C is characterized by the inability to control coagulation, resulting in the excessive formation of blood clots (thrombophilia). Protein C deficiency may be acquired or congenital. Congenital protein C deficiency results from mutations in the PROC gene. More than 160 PROC mutations have been described and may result in reduced levels of protein C (Type I) or the production of an altered protein C molecule with decreasing levels of activity (Type II). Protein C deficiency is an autosomal dominant condition. Mutations in a single copy in heterozygous individuals cause mild protein C deficiency, whereas individuals with homozygous mutations present with severe protein C deficiency. Protein C is a vitamin K-dependent protease circulating in plasma at low concentrations and serves a critical role in the regulation of thrombin. Levels of protein C mature later than many other coagulation proteins, with levels increasing from birth until 6 months and into puberty. Protein C becomes activated to form activated protein C (APC) via interactions with thrombin. APC acts to downregulate coagulation by cleaving and inactivating clotting factors V and VIII. A deficiency of protein C, and thus APC activity, leads to an inability to inactivate clotting factors and control thrombin production. Protein C is also known to have a role in the regulation of inflammation and sepsis, with demonstrated cytoprotective functions.
Protein C deficiency is less common than either the factor V Leiden or the prothrombin G20210A gene mutation with prevalence in Caucasians estimated to be 0.2–0.5%. Protein C deficiency is inherited in an autosomal dominant manner and is associated with familial venous thrombosis. The gene for protein C is located on chromosome 2 (2q13–14) and appears to be closely related to the gene for factor IX. The primary effect of activated protein C (APC) is to inactivate coagulation factors Va and VIIIa, which are necessary for efficient thrombin generation and factor X activation. The inhibitory effect of APC is markedly enhanced by protein S, another vitamin K-dependent protein.


Two major subtypes of heterozygous protein C deficiency (Type I and Type II) have been delineated using immunologic and functional assays. Over 160 different gene abnormalities have been associated with the two subtypes.
===Antithrombin III (ATIII) deficiency===
Type I deficiency – The type I deficiency state is more common. Most affected patients are heterozygous, having a reduced plasma protein C concentration at approximately 50 percent of normal in both immunologic and functional assays. More than half of the mutations identified so far are missense and nonsense mutations. Other types of mutations include promoter mutations, splice site abnormalities. in-frame deletions, frameshift deletions, in-frame insertions, and frameshift insertions. There is marked phenotypic variability among patients with heterozygous type I protein C deficiency. Similar mutations have been found among symptomatic and asymptomatic individuals. This finding suggests that the nature of the protein C gene defect alone does not explain the phenotypic variability.
*'''Antithrombin''' (previously called antithrombin III) is synthesized by the liver but is not vitamin K-dependent. Its inhibitory effect is not confined to thrombin. It also inhibits the activated clotting factors IXa, Xa, XIa, XIIa and tissue factor-bound factor VIIa. Antithrombin III binds to heparin on endothelial cells and forms a complex between antithrombin and the serine proteases and thus, inhibiting coagulation. Mutations in [[antithrombin]] can lead to increased thrombus formation. <ref name="pmid14347873">{{cite journal| author=EGEBERG O| title=INHERITED ANTITHROMBIN DEFICIENCY CAUSING THROMBOPHILIA. | journal=Thromb Diath Haemorrh | year= 1965 | volume= 13 | issue=  | pages= 516-30 | pmid=14347873 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14347873}} </ref> <ref name="WalkerGreaves2001">{{cite journal|last1=Walker|first1=Isobel D|last2=Greaves|first2=M|last3=Preston|first3=F. E|title=Investigation and management of heritable thrombophilia|journal=British Journal of Haematology|volume=114|issue=3|year=2001|pages=512–528|issn=00071048|doi=10.1046/j.1365-2141.2001.02981.x}}</ref>
Type II deficiency – Individuals with the type II deficiency state have normal plasma protein C antigen levels with decreased functional activity. A variety of different point mutations affecting protein function have been identified in this disorder.
*The '''prevalence''' may be 1 in 500 in the general population. Affected patients have antithrombin levels 40–60% of normal, and 70% of those affected experience thrombo-embolic events before the age of 50. Thrombotic episodes are rare before puberty in AT-deficient individuals. They start to occur with some frequency after puberty, with the risk increasing substantially with advancing age. <ref name="urlHypercoagulability - StatPearls - NCBI Bookshelf">{{cite web |url=https://www.ncbi.nlm.nih.gov/books/NBK538251/ |title=Hypercoagulability - StatPearls - NCBI Bookshelf |format= |work= |accessdate=}}</ref> <ref name="pmid7032781">{{cite journal| author=Thaler E, Lechner K| title=Antithrombin III deficiency and thromboembolism. | journal=Clin Haematol | year= 1981 | volume= 10 | issue= 2 | pages= 369-90 | pmid=7032781 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7032781  }} </ref>
*'''Type of inheritance:''' Antithrombin (AT) deficiency is a heterogeneous disorder. It is usually inherited in an autosomal dominant fashion, thereby affecting both sexes equally. Homozygous ATIII deficiency is incompatible with life unless affecting the heparin-binding site. <ref name="pmid10957782">{{cite journal| author=März W, Nauck M, Wieland H| title=The molecular mechanisms of inherited thrombophilia. | journal=Z Kardiol | year= 2000 | volume= 89 | issue= 7 | pages= 575-86 | pmid=10957782 | doi=10.1007/s003920070206 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10957782  }} </ref>
*'''Causes:''' ATIII deficiency can occur as a consequence of reduced synthesis (liver damage) or increased loss (nephrotic syndrome, enteropathy, DIC, sepsis, burn, trauma, microangiopathy, and cardiopulmonary bypass surgery). Usually these patients present with venous thrombosis and less likely with arterial thrombosis. <ref name="pmid25025009">{{cite journal| author=Nakashima MO, Rogers HJ| title=Hypercoagulable states: an algorithmic approach to laboratory testing and update on monitoring of direct oral anticoagulants. | journal=Blood Res | year= 2014 | volume= 49 | issue= 2 | pages= 85-94 | pmid=25025009 | doi=10.5045/br.2014.49.2.85 | pmc=4090343 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25025009  }} </ref>
*'''Classification:''' Three major types of heritable AT deficiency are recognized as follows: <ref name="WalkerGreaves2001">{{cite journal|last1=Walker|first1=Isobel D|last2=Greaves|first2=M|last3=Preston|first3=F. E|title=Investigation and management of heritable thrombophilia|journal=British Journal of Haematology|volume=114|issue=3|year=2001|pages=512–528|issn=00071048|doi=10.1046/j.1365-2141.2001.02981.x}}</ref>
**'''Type I:''' It is characterized by a quantitative reduction of qualitatively (functionally) normal antithrombin protein and thereby reducing both the antigenic and functional activity of AT in the blood. The values are reduced by approximately 50 percent in the heterozygote. The 1997 antithrombin mutation database included 80 distinct mutations in patients with type I deficiency. The database shows that the molecular basis for this disorder is usually a small deletion or insertion (less than 22 base pairs) or a deletion of a major segment of the AT gene. <ref name="pmid7082848">{{cite journal| author=Ambruso DR, Leonard BD, Bies RD, Jacobson L, Hathaway WE, Reeve EB| title=Antithrombin III deficiency: decreased synthesis of a biochemically normal molecule. | journal=Blood | year= 1982 | volume= 60 | issue= 1 | pages= 78-83 | pmid=7082848 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7082848  }} </ref> <ref name="pmid9031473">{{cite journal| author=Lane DA, Bayston T, Olds RJ, Fitches AC, Cooper DN, Millar DS | display-authors=etal| title=Antithrombin mutation database: 2nd (1997) update. For the Plasma Coagulation Inhibitors Subcommittee of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis. | journal=Thromb Haemost | year= 1997 | volume= 77 | issue= 1 | pages= 197-211 | pmid=9031473 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=9031473  }} </ref> 
**'''Type II:''' It is produced by a discrete molecular qualitative mutational defect within the protein which either affect the heparin-binding site (HBS), the reactive site (RS) or result in pleiotropic effects (PE). While the AT immunologic activity is normal in this deficiency, plasma AT functional activity is markedly reduced leading to risk of thrombosis. It is subclassified according to the site of the molecular defect: <ref name="pmid10957782">{{cite journal| author=März W, Nauck M, Wieland H| title=The molecular mechanisms of inherited thrombophilia. | journal=Z Kardiol | year= 2000 | volume= 89 | issue= 7 | pages= 575-86 | pmid=10957782 | doi=10.1007/s003920070206 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10957782  }} </ref> <ref name="pmid15806273">{{cite journal| author=Johnson CM, Mureebe L, Silver D| title=Hypercoagulable states: a review. | journal=Vasc Endovascular Surg | year= 2005 | volume= 39 | issue= 2 | pages= 123-33 | pmid=15806273 | doi=10.1177/153857440503900201 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15806273  }} </ref>
***'''Reactive site''' (RS) and abnormalities residing in the reactive (thrombin binding) site.
***'''Heparin binding site''' (HBS) and abnormalities residing in the heparin binding site.
***'''Pleiotropic effect''' (PE) and abnormalities residing in both reactive and heparin binding sites.
**'''Type III:''' This type is characterized by normal functional and antigenic antithrombin levels but impaired interaction between AT and heparin. <ref name="pmid7947234">{{cite journal| author=Tait RC, Walker ID, Perry DJ, Islam SI, Daly ME, McCall F | display-authors=etal| title=Prevalence of antithrombin deficiency in the healthy population. | journal=Br J Haematol | year= 1994 | volume= 87 | issue= 1 | pages= 106-12 | pmid=7947234 | doi=10.1111/j.1365-2141.1994.tb04878.x | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7947234  }} </ref>


Homozygotes can develop a severe thrombotic tendency in infancy characterized as purpura fulminans. Heterozygotes for protein C deficiency have an increased risk of developing warfarin-induced skin necrosis. Protein C deficiency has been implicated in adverse pregnancy outcomes such as DVT, preeclampsia, intrauterine growth restriction and recurrent pregnancy loss.
===Protein C deficiency===
*Protein C is a '''vitamin K-dependent protease''' synthesized in the liver and circulates in plasma at low concentrations which serves a critical role in the regulation of thrombin. Protein C becomes activated to form '''activated protein C (APC)''' via interactions with thrombin. APC acts as one of the major inhibitors of the coagulation system by cleaving and inactivating clotting factors V and VIII which are necessary for efficient thrombin generation, and thereby exerting potent anticoagulant activity. Moreover, APC also reduces platelet prothrombinase activity by degrading platelet bound factor Va at the receptor for factor Xa. Additionally, the inhibitory effects of APC are facilitated through the cofactor activity of protein S, another vitamin K-dependent protein. <ref name="WalkerGreaves2001">{{cite journal|last1=Walker|first1=Isobel D|last2=Greaves|first2=M|last3=Preston|first3=F. E|title=Investigation and management of heritable thrombophilia|journal=British Journal of Haematology|volume=114|issue=3|year=2001|pages=512–528|issn=00071048|doi=10.1046/j.1365-2141.2001.02981.x}}</ref><ref name="pmid17110453">{{cite journal| author=Mosnier LO, Zlokovic BV, Griffin JH| title=The cytoprotective protein C pathway. | journal=Blood | year= 2007 | volume= 109 | issue= 8 | pages= 3161-72 | pmid=17110453 | doi=10.1182/blood-2006-09-003004 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17110453  }} </ref> 
*'''Protein C deficiency''' is a rare acquired or congenital disorder characterized by a reduction in the activity of protein C, a plasma serine protease involved in the regulation of blood coagulation which results in the excessive formation of blood clots (thrombophilia).
*'''Congenital''' protein C deficiency results from mutations in the '''PROC gene''' and inherited in an '''autosomal dominant''' manner. The gene for protein C is located on '''chromosome 2 (2q13–14)''' and appears to be closely related to the gene for factor IX. <ref name="pmid2991887">{{cite journal| author=Foster DC, Yoshitake S, Davie EW| title=The nucleotide sequence of the gene for human protein C. | journal=Proc Natl Acad Sci U S A | year= 1985 | volume= 82 | issue= 14 | pages= 4673-7 | pmid=2991887 | doi=10.1073/pnas.82.14.4673 | pmc=390448 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=2991887  }} </ref>
*'''Mode of inheritance:''' <ref name="pmid10669160">{{cite journal| author=Alhenc-Gelas M, Gandrille S, Aubry ML, Aiach M| title=Thirty-three novel mutations in the protein C gene. French INSERM network on molecular abnormalities responsible for protein C and protein S. | journal=Thromb Haemost | year= 2000 | volume= 83 | issue= 1 | pages= 86-92 | pmid=10669160 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10669160  }} </ref>
**'''Heterozygous:''' Mutations in a single copy in heterozygous individuals cause '''mild''' protein C deficiency.
**'''Homozygous:''' Individuals with homozygous mutations present with '''severe''' protein C deficiency and thrombotic tendency in infancy characterized as purpura fulminans. <ref name="pmid3397801">{{cite journal| author=Manco-Johnson MJ, Marlar RA, Jacobson LJ, Hays T, Warady BA| title=Severe protein C deficiency in newborn infants. | journal=J Pediatr | year= 1988 | volume= 113 | issue= 2 | pages= 359-63 | pmid=3397801 | doi=10.1016/s0022-3476(88)80284-1 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3397801  }} </ref>
*'''Inherited:''' Two major subtypes of heterozygous protein C deficiency have been delineated using immunologic and functional assays. Over 160 different gene abnormalities have been associated with the two subtypes.<ref name="pmid10669160">{{cite journal| author=Alhenc-Gelas M, Gandrille S, Aubry ML, Aiach M| title=Thirty-three novel mutations in the protein C gene. French INSERM network on molecular abnormalities responsible for protein C and protein S. | journal=Thromb Haemost | year= 2000 | volume= 83 | issue= 1 | pages= 86-92 | pmid=10669160 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10669160  }} </ref> <ref name="pmid7482420">{{cite journal| author=Reitsma PH, Bernardi F, Doig RG, Gandrille S, Greengard JS, Ireland H | display-authors=etal| title=Protein C deficiency: a database of mutations, 1995 update. On behalf of the Subcommittee on Plasma Coagulation Inhibitors of the Scientific and Standardization Committee of the ISTH. | journal=Thromb Haemost | year= 1995 | volume= 73 | issue= 5 | pages= 876-89 | pmid=7482420 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7482420  }} </ref>
**'''Type I:''' This state is more common with a reduced plasma protein C concentration at approximately 50% of normal in both immunologic and functional assays. Most affected patients are heterozygous and carries an increased risk of developing warfarin-induced skin necrosis. More than half of the mutations are missense and nonsense mutations and other includes promoter mutations, splice site mutations, in-frame deletions, frameshift deletions, in-frame insertions, and frameshift insertions. Moreover, there is marked phenotypic variability among patients with heterozygous type I protein C deficiency. Similar mutations have been found among symptomatic and asymptomatic individuals which suggests that the nature of the protein C gene defect alone does not explain the phenotypic variability. <ref name="pmid7482420">{{cite journal| author=Reitsma PH, Bernardi F, Doig RG, Gandrille S, Greengard JS, Ireland H | display-authors=etal| title=Protein C deficiency: a database of mutations, 1995 update. On behalf of the Subcommittee on Plasma Coagulation Inhibitors of the Scientific and Standardization Committee of the ISTH. | journal=Thromb Haemost | year= 1995 | volume= 73 | issue= 5 | pages= 876-89 | pmid=7482420 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7482420  }} </ref> <ref>Broekmans AW, Bertina RM, Protein C: In: Recent Advances in Blood Coagulation. Volume 4. Edited by: Poller L. Churchill Livingstone New York; 1985:117.</ref>
**'''Type II:''' It has normal plasma protein C antigen levels with decreased functional activity; and a variety of different point mutations affecting protein function have been identified in this disorder. <ref name="pmid7482420">{{cite journal| author=Reitsma PH, Bernardi F, Doig RG, Gandrille S, Greengard JS, Ireland H | display-authors=etal| title=Protein C deficiency: a database of mutations, 1995 update. On behalf of the Subcommittee on Plasma Coagulation Inhibitors of the Scientific and Standardization Committee of the ISTH. | journal=Thromb Haemost | year= 1995 | volume= 73 | issue= 5 | pages= 876-89 | pmid=7482420 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7482420  }} </ref>
*'''Acquired:''' Protein C is known to have a role in the regulation of inflammation and sepsis which demonstrates its cytoprotective functions. Reduced protein C activity is observed in DIC, liver disease, coumarins use, and adverse pregnancy outcomes such as DVT, preeclampsia, intrauterine growth restriction and recurrent pregnancy loss. <ref name="pmid17110453">{{cite journal| author=Mosnier LO, Zlokovic BV, Griffin JH| title=The cytoprotective protein C pathway. | journal=Blood | year= 2007 | volume= 109 | issue= 8 | pages= 3161-72 | pmid=17110453 | doi=10.1182/blood-2006-09-003004 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17110453  }} </ref> <ref name="pmid12787535">{{cite journal| author=Greer IA| title=Inherited thrombophilia and venous thromboembolism. | journal=Best Pract Res Clin Obstet Gynaecol | year= 2003 | volume= 17 | issue= 3 | pages= 413-25 | pmid=12787535 | doi=10.1016/s1521-6934(03)00007-5 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12787535  }} </ref>
*Additionally, the half-life of protein C is shorter than the half-life of other vitamin K-dependent coagulation factors; hence, the risk of increased coagulation with the initiation of vitamin K antagonists can be seen; and thereby need the bridging with parenteral heparin to avoid warfarin-induced skin necrosis.


*'''Protein S deficiency:''' Protein S deficiency is usually congenital, caused by mutations in the PROS1 gene. More than 200 PROS mutations have been described and may result in three different forms of protein S deficiency:
===Protein S deficiency <ref name="urlProtein S Deficiency - StatPearls - NCBI Bookshelf">{{cite web |url=https://www.ncbi.nlm.nih.gov/books/NBK544344/ |title=Protein S Deficiency - StatPearls - NCBI Bookshelf |format= |work= |accessdate=}}</ref>===
**Type I: quantitative defect presenting with low levels of total protein S (TPS) and free protein S (FPS), with reduced levels of protein S activity.Type I – The classic type of protein S deficiency is associated with a decreased level of total S antigen (approximately 50% of normal), and marked reductions in free protein S antigen and protein S functional activity.
*Protein S is a '''vitamin K-dependent protease''' that circulates in plasma at low concentrations and serves a crucial role in the regulation of coagulation.
**Type II (also known as Type IIb): Decreased protein S activity, with normal levels of TPS and FPS antigens. This type of protein S deficiency is characterized by normal total and free protein S levels, but diminished protein S functional activity. Interestingly, all five mutations originally described in these patients were missense mutations located in the N-terminal end of the protein S molecule, which includes the domains that interact with activated protein C.
*In circulation, approximately 40% of protein S is free, remains uncomplexed and is the active moiety; while about 60% is in a high-affinity complex with the complement regulatory factor C4b-binding protein (C4BP) and has no cofactor activity. The bioavailability of protein S is closely linked to the concentration of C4bBP, which acts as an important regulatory protein in the activated protein C:protein S inhibitory pathway. <ref name="pmid18695379">{{cite journal| author=Castoldi E, Hackeng TM| title=Regulation of coagulation by protein S. | journal=Curr Opin Hematol | year= 2008 | volume= 15 | issue= 5 | pages= 529-36 | pmid=18695379 | doi=10.1097/MOH.0b013e328309ec97 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18695379  }} </ref>
**Type III (also known as Type IIa): quantitative defect presenting with normal levels of TPS, but reduced levels of FPS and protein S activity. This is characterized by total protein S antigen measurements in the normal range and selectively reduced levels of free protein S and protein S functional activity to less than approximately 40 percent of normal.
*The '''anticoagulant activity''' of protein S is two-fold as follows: <ref name="pmid28905350">{{cite journal| author=Dahlbäck B| title=Vitamin K-Dependent Protein S: Beyond the Protein C Pathway. | journal=Semin Thromb Hemost | year= 2018 | volume= 44 | issue= 2 | pages= 176-184 | pmid=28905350 | doi=10.1055/s-0037-1604092 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=28905350  }} </ref>
Protein S deficiency is an autosomal dominant pathology. Mutations in a single copy in heterozygous individuals cause mild protein S deficiency, whereas individuals with homozygous mutations present with severe protein S deficiency. Causes of temporary acquired fluctuations in protein S levels may include vitamin K-antagonist therapy, chronic infections, severe hepatic disease, nephritic syndrome, and DIC. The risk of VTE is also increased in patients using oral contraceptives and pregnancy. Protein S is a vitamin K-dependent protease that circulates in plasma at low concentrations and serves a crucial role in the regulation of coagulation. In circulation, approximately 40% of protein S is free, and about 60% is in a high-affinity complex with the complement regulatory factor C4b-binding protein (C4BP). The anticoagulant activity of protein S is two-fold: Protein S operates as a cofactor for activated protein C (APC), and inactivating coagulation Factor Va and Factor VIIIa; and Protein S is also a cofactor for the tissue factor pathway inhibitor (TFPI) protein, resulting in the inactivation of Factor Xa and tissue factor (TF)/Factor VIIa. Protein S is a complex protein with multiple structural moieties. The 3-dimensional structure is yet to be resolved but is expected to contribute to the understanding of the complex functional nature of PROS1 mutations.
**Protein S operates as a cofactor for activated protein C (APC) and inactivates coagulation Factor Va and Factor VIIIa;
**Protein S is also a cofactor for the tissue factor pathway inhibitor (TFPI) protein resulting in the inactivation of Factor Xa and tissue factor (TF)/Factor VIIa.
*Protein S deficiency is usually congenital caused by mutations in the '''PROS1 gene''' and mainly an autosomal dominant pathology. <ref name="pmid18695379">{{cite journal| author=Castoldi E, Hackeng TM| title=Regulation of coagulation by protein S. | journal=Curr Opin Hematol | year= 2008 | volume= 15 | issue= 5 | pages= 529-36 | pmid=18695379 | doi=10.1097/MOH.0b013e328309ec97 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18695379  }} </ref>
*'''Mode of inheritance:'''
**'''Heterozygous:''' Mutations in a single copy in heterozygous individuals cause '''mild''' protein S deficiency
**'''Homozygous:''' Individuals with homozygous mutations present with '''severe''' protein S deficiency
*'''Inherited:''' More than 200 PROS mutations have been described and may result in three different forms of protein S deficiency: <ref name="pmid18695379">{{cite journal| author=Castoldi E, Hackeng TM| title=Regulation of coagulation by protein S. | journal=Curr Opin Hematol | year= 2008 | volume= 15 | issue= 5 | pages= 529-36 | pmid=18695379 | doi=10.1097/MOH.0b013e328309ec97 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=18695379  }} </ref>
**'''Type I:''' It is a quantitative defect presenting with low levels of total protein S (TPS) and free protein S (FPS) with reduced levels of functional protein S activity. <ref name="pmid8943854">{{cite journal| author=Simmonds RE, Ireland H, Kunz G, Lane DA| title=Identification of 19 protein S gene mutations in patients with phenotypic protein S deficiency and thrombosis. Protein S Study Group. | journal=Blood | year= 1996 | volume= 88 | issue= 11 | pages= 4195-204 | pmid=8943854 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8943854  }} </ref>
**'''Type II (or Type IIb):''' This type of protein S deficiency is characterized by decreased functional protein S activity with normal levels of TPS and FPS antigens. Interestingly, all five mutations originally described were missense mutations located in the N-terminal end of the protein S molecule consisting of the domains that interact with activated protein C. <ref name="pmid7803790">{{cite journal| author=Gandrille S, Borgel D, Eschwege-Gufflet V, Aillaud M, Dreyfus M, Matheron C | display-authors=etal| title=Identification of 15 different candidate causal point mutations and three polymorphisms in 19 patients with protein S deficiency using a scanning method for the analysis of the protein S active gene. | journal=Blood | year= 1995 | volume= 85 | issue= 1 | pages= 130-8 | pmid=7803790 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7803790  }} </ref>
**'''Type III (or Type IIa):''' It consists of a quantitative defect presenting with normal levels of TPS, but selectively reduced levels of FPS and functional protein S activity to less than approximately 40 percent of normal. <ref name="pmid7989612">{{cite journal| author=Zöller B, Svensson PJ, He X, Dahlbäck B| title=Identification of the same factor V gene mutation in 47 out of 50 thrombosis-prone families with inherited resistance to activated protein C. | journal=J Clin Invest | year= 1994 | volume= 94 | issue= 6 | pages= 2521-4 | pmid=7989612 | doi=10.1172/JCI117623 | pmc=330087 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7989612  }} </ref>
*'''Acquired:''' Causes of temporary acquired fluctuations in protein S levels may include vitamin K-antagonist therapy (coumarins), antiphospholipid antibodies, chronic infections, severe hepatic disease, nephritic syndrome, and DIC. <ref name="pmid12907438">{{cite journal| author=Rezende SM, Simmonds RE, Lane DA| title=Coagulation, inflammation, and apoptosis: different roles for protein S and the protein S-C4b binding protein complex. | journal=Blood | year= 2004 | volume= 103 | issue= 4 | pages= 1192-201 | pmid=12907438 | doi=10.1182/blood-2003-05-1551 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12907438  }} </ref>
*'''Gender predilection:''' Protein S levels are slightly higher in men than in women. Contrarily, protein S levels fall progressively during pregnancy and are reduced to a lesser extent in women using oestrogen containing oral contraceptives or hormone replacement therapy. Moreover, the risk of VTE is also increased in patients using oral contraceptives and pregnancy. <ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638  }} </ref> <ref name="pmid17296885">{{cite journal| author=van Vlijmen EF, Brouwer JL, Veeger NJ, Eskes TK, de Graeff PA, van der Meer J| title=Oral contraceptives and the absolute risk of venous thromboembolism in women with single or multiple thrombophilic defects: results from a retrospective family cohort study. | journal=Arch Intern Med | year= 2007 | volume= 167 | issue= 3 | pages= 282-9 | pmid=17296885 | doi=10.1001/archinte.167.3.282 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=17296885  }} </ref>


*'''Factor V Leiden mutation:''' Protein C interacts with thrombomodulin to become activated protein C (APC). APC has anticoagulant, anti-inflammatory, and cytoprotective properties and has been proposed for the treatment of sepsis. The signal cascade leading to APC can become distorted through many acquired or inherited mechanisms leading to APC resistance. Activated protein C inactivates coagulation factors V and VIII. The factor V Leiden mutation is a common cause for APC resistance and the most frequent genetic thrombophilia. The FV Leiden mutation is also suspected of increasing the risk of arterial thrombosis. Other FV mutations include factor V Cambridge and factor V Hong Kong. The most common genetic risk factor for thrombophilia is Factor V Leiden mutation. It increases the risk of thrombosis by enhanced thrombin production.  
===Factor V Leiden mutation===
*The most common inherited thrombophilia is [[Factor V Leiden]] which is a polymorphism of Factor V that is resistant to APC inactivation. Other FV mutations include factor V Cambridge and factor V Hong Kong. <ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638  }} </ref> <ref name="pmid15806273">{{cite journal| author=Johnson CM, Mureebe L, Silver D| title=Hypercoagulable states: a review. | journal=Vasc Endovascular Surg | year= 2005 | volume= 39 | issue= 2 | pages= 123-33 | pmid=15806273 | doi=10.1177/153857440503900201 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15806273  }} </ref> <ref name="pmid15139558">{{cite journal| author=Mazza JJ| title=Hypercoagulability and venous thromboembolism: a review. | journal=WMJ | year= 2004 | volume= 103 | issue= 2 | pages= 41-9 | pmid=15139558 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15139558  }} </ref>
*'''Activated protein C (APC):''' Protein C interacts with thrombomodulin to become APC which has anticoagulant, anti-inflammatory, and cytoprotective properties. The signal cascade leading to APC can become distorted through many acquired or inherited mechanisms leading to APC resistance. Hence, '''[[Activated protein C resistance|APC resistance]]''' occurs when APC fails to inactivate downstream coagulation factors, specifically [[Factor_V|Factor V]] and [[Factor_VIII|Factor VIII]]. <ref name="pmid25025009">{{cite journal| author=Nakashima MO, Rogers HJ| title=Hypercoagulable states: an algorithmic approach to laboratory testing and update on monitoring of direct oral anticoagulants. | journal=Blood Res | year= 2014 | volume= 49 | issue= 2 | pages= 85-94 | pmid=25025009 | doi=10.5045/br.2014.49.2.85 | pmc=4090343 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25025009  }} </ref> 
*The factor V Leiden mutation further increases arterial thrombosis risk by enhancing thrombin production. Protein C and S are natural anticoagulants which inhibit thrombin formation. Dysregulation in APC can occur as either defects in the protein C or S molecule (Protein C and S deficiency) or as resistance to APC activity.<ref name="pmid11309638">{{cite journal| author=Seligsohn U, Lubetsky A| title=Genetic susceptibility to venous thrombosis. | journal=N Engl J Med | year= 2001 | volume= 344 | issue= 16 | pages= 1222-31 | pmid=11309638 | doi=10.1056/NEJM200104193441607 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11309638  }} </ref> <ref name="pmid10957782">{{cite journal| author=März W, Nauck M, Wieland H| title=The molecular mechanisms of inherited thrombophilia. | journal=Z Kardiol | year= 2000 | volume= 89 | issue= 7 | pages= 575-86 | pmid=10957782 | doi=10.1007/s003920070206 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10957782  }} </ref> <ref name="urlFactor V Leiden Deficiency - StatPearls - NCBI Bookshelf">{{cite web |url=https://www.ncbi.nlm.nih.gov/books/NBK534802/ |title=Factor V Leiden Deficiency - StatPearls - NCBI Bookshelf |format= |work= |accessdate=}}</ref>


*'''Prothrombin G20210A mutation:'''Prothrombin is the precursor of thrombin, which is factor II. The prothrombin G20210A mutation is the second most common inherited risk factor for thrombosis and leads to increased levels of prothrombin which demonstrates a higher risk for arterial and venous thrombotic events. It is due to a single point mutation. It is seen commonly in Caucasians. Prothrombin (factor II) is the precursor to thrombin, the end-product of the coagulation cascade. Prothrombin has procoagulant, anticoagulant and antifibrinolytic activities and thus a disorder involving prothrombin results in multiple imbalances in hemostasis. The prothrombin G20210A gene mutation is associated with an elevated risk of deep vein thrombosis, although to a lesser degree than factor V Leiden is.
===Prothrombin G20210A mutation===
*Prothrombin (factor II) is the precursor to thrombin, the end-product of the coagulation cascade. Prothrombin has procoagulant, anticoagulant and antifibrinolytic activities and thus a disorder involving prothrombin results in multiple hemostasis imbalances.
*It is the '''second most common''' inherited thrombophilia which involves a gain of function mutation of the prothrombin gene ([https://en.wikipedia.org/wiki/Prothrombin_G20210A Prothrombin G20210A]) resulting in increased protein activity and thrombus formation. <ref name="pmid15806273">{{cite journal| author=Johnson CM, Mureebe L, Silver D| title=Hypercoagulable states: a review. | journal=Vasc Endovascular Surg | year= 2005 | volume= 39 | issue= 2 | pages= 123-33 | pmid=15806273 | doi=10.1177/153857440503900201 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15806273  }} </ref> <ref name="pmid15139558">{{cite journal| author=Mazza JJ| title=Hypercoagulability and venous thromboembolism: a review. | journal=WMJ | year= 2004 | volume= 103 | issue= 2 | pages= 41-9 | pmid=15139558 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15139558  }} </ref> <ref name="pmid8916933">{{cite journal| author=Poort SR, Rosendaal FR, Reitsma PH, Bertina RM| title=A common genetic variation in the 3'-untranslated region of the prothrombin gene is associated with elevated plasma prothrombin levels and an increase in venous thrombosis. | journal=Blood | year= 1996 | volume= 88 | issue= 10 | pages= 3698-703 | pmid=8916933 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8916933  }} </ref>
*It is due to a '''single point mutation''' which involves the G to A transition at nucleotide 20210 in the 30-untranslated region of the prothrombin gene and thereby associated with elevated plasma prothrombin levels and demonstrating a higher risk for arterial and venous thrombotic events. <ref name="pmid8916933">{{cite journal| author=Poort SR, Rosendaal FR, Reitsma PH, Bertina RM| title=A common genetic variation in the 3'-untranslated region of the prothrombin gene is associated with elevated plasma prothrombin levels and an increase in venous thrombosis. | journal=Blood | year= 1996 | volume= 88 | issue= 10 | pages= 3698-703 | pmid=8916933 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8916933  }} </ref>


*'''Hyperhomocysteinemia:''' It is associated with premature atherosclerosis and thrombosis and caused by defects of the methionine metabolic pathway. Deficiencies of cofactors of this pathway such as vitamin B6, B12, and folate or defects of enzymes such as cystathionine beta-synthase (CBS) or methylenetetrahydrofolate reductase (MTHFR) decrease the efficiency of homocysteine metabolism. Furthermore renal failure, hypothyroidism, and drugs such as methotrexate, phenytoin, and carbamazepine increase homocysteine levels. On the other hand, lowering homocysteine levels has not been shown to reduce thrombotic risk.
===Hyperhomocysteinemia===
Hyperhomocysteinemia may be both a genetic and acquired abnormality. Homocystinuria and hyperhomocysteinemia can be caused by rare inborn errors of metabolism that result in marked elevations of plasma and urine homocysteine concentrations. Homocysteine is an amino acid derived from methionine. Hyperhomocysteinemia occurs when increased amounts of the amino acid accumulate in the blood due to of impaired intracellular metabolism of homocysteine. Homocysteine is metabolized by the body in two possible pathways: transsulfuration, and remethylation. The transsulfuration of homocysteine produces cysteine and the reaction is catalyzed by cystathionine-β-synthase. This process requires pyridoxal phosphate (Vitamin B) as a cofactor. Remethylation of homocysteine produces methionine. This reaction is catalyzed either by methionine synthase or by betaine homocysteine methyltransferase. Vitamin B12 (cobalamin) is the precursor of methylcobalamin, which is the cofactor for methionine synthase. Elevations in the plasma homocysteine concentration can occur due to genetic defects in the enzymes involved in homocysteine metabolism as well as due to nutritional deficiencies in vitamin cofactors, or to other factors including some chronic medical conditions and drugs. Premature atherosclerosis and arterial thrombosis is associated with severe hyperhomocysteinemia.
*'''Homocystinuria''' and '''hyperhomocysteinemia''' are rare metabolism disorder associated with the marked elevations of plasma and urine homocysteine concentrations resulting from an impaired intracellular metabolism of homocysteine which can be due to both genetic and acquired abnormality.
*Homocysteine is an amino acid derived from methionine which is metabolized by the body in two possible following pathways: <ref name="KhanDickerman2006">{{cite journal|last1=Khan|first1=Salwa|last2=Dickerman|first2=Joseph D|journal=Thrombosis Journal|volume=4|issue=1|year=2006|pages=15|issn=14779560|doi=10.1186/1477-9560-4-15}}</ref>
**'''Transsulfuration''' of homocysteine produces cysteine, and this reaction is catalyzed by cystathionine-β-synthase which requires pyridoxal phosphate (Vitamin B) as a cofactor.  
**'''Remethylation''' of homocysteine produces methionine which is catalyzed either by methionine synthase or by betaine homocysteine methyltransferase. Vitamin B12 (cobalamin) is the precursor of methylcobalamin, which is the cofactor for methionine synthase.
*'''Nutritional deficiencies''' in vitamin cofactors such as vitamin B6, B12, and folate or genetic defects of enzymes such as cystathionine beta-synthase (CBS) or methylenetetrahydrofolate reductase (MTHFR) decrease the efficiency of homocysteine metabolism. Furthermore, '''chronic medical conditions''' such as renal failure, hypothyroidism, and '''drugs''' such as methotrexate, phenytoin, and carbamazepine increase homocysteine levels. <ref name="pmid10957782">{{cite journal| author=März W, Nauck M, Wieland H| title=The molecular mechanisms of inherited thrombophilia. | journal=Z Kardiol | year= 2000 | volume= 89 | issue= 7 | pages= 575-86 | pmid=10957782 | doi=10.1007/s003920070206 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10957782  }} </ref> <ref name="pmid15806273">{{cite journal| author=Johnson CM, Mureebe L, Silver D| title=Hypercoagulable states: a review. | journal=Vasc Endovascular Surg | year= 2005 | volume= 39 | issue= 2 | pages= 123-33 | pmid=15806273 | doi=10.1177/153857440503900201 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15806273  }} </ref> <ref name="pmid15139558">{{cite journal| author=Mazza JJ| title=Hypercoagulability and venous thromboembolism: a review. | journal=WMJ | year= 2004 | volume= 103 | issue= 2 | pages= 41-9 | pmid=15139558 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15139558  }} </ref>
*Hence, premature atherosclerosis and arterial thrombosis is associated with severe hyperhomocysteinemia.


*'''Elevated factor VIII (FVIII):''' It increases the risk of thrombosis. African-Americans appear to have higher levels whereas individuals with blood group O tend to have lower levels of FVIII. High levels of this factor also correlate with acute phase reactions, estrogen usage, pregnancy, and after aerobic exercise. A high FVIII level may cause APC resistance not due to FV mutation. In contrast, low levels of FVIII correlate with bleeding in hemophilia A patients.  
===Elevated factor VIII (FVIII)<ref name="pmid10957782">{{cite journal| author=März W, Nauck M, Wieland H| title=The molecular mechanisms of inherited thrombophilia. | journal=Z Kardiol | year= 2000 | volume= 89 | issue= 7 | pages= 575-86 | pmid=10957782 | doi=10.1007/s003920070206 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10957782  }} </ref> <ref name="pmid25025009">{{cite journal| author=Nakashima MO, Rogers HJ| title=Hypercoagulable states: an algorithmic approach to laboratory testing and update on monitoring of direct oral anticoagulants. | journal=Blood Res | year= 2014 | volume= 49 | issue= 2 | pages= 85-94 | pmid=25025009 | doi=10.5045/br.2014.49.2.85 | pmc=4090343 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25025009  }} </ref>===
*'''Higher levels:''' African-Americans appear to have its higher levels. It further increases the risk of thrombosis, and found to be correlated with acute phase reactions, estrogen usage, pregnancy, and aerobic exercise.  
*'''Lower levels:''' Individuals with blood group "O" tend to have lower levels of FVIII and correlated with bleeding in hemophilia A patients.


*'''Dysfibrinolysis:''' plasminogen deficiency, dysfibrinogenemia, tissue plasminogen activator (tPA) deficiency, plasminogen activator inhibitor (PAI) increase, and factor XII deficiency, which is involved in plasmin generation. Deficient plasminogen clinically appears similar to protein c deficiency with thrombosis during the teenage years. PAI increase and deficient tPA has an association with diabetes mellitus, inflammatory bowel syndrome and coronary atherosclerosis. In patients with structural or functional changes to fibrinogen (dysfibrinogenemia) thrombosis or bleeding can occur. The abnormal production of fibrinogen can result in dysfibrinogenemia. The abnormal fibrinogen usually exhibits an abnormal thrombin-mediated conversion to fibrin. In 1984, Lijnen et al reported that the fibrin-mediated enhancement of the activation of plasminogen by tissue type plasminogen activator observed with normal fibrin is strongly decreased with the abnormal type known as fibrin Dusard, although the binding of tissue-type plasminogen activator to the fibrin was normal. They suggested that this impaired fibrin-mediated plasminogen activation is most likely the cause of thrombophilia among affected patients. While most patients with dysfibrinogenemia are clinically asymptomatic, some present with a bleeding diathesis, others with thrombophilia, and occasionally with both, bleeding and thromboembolism.
===Dysfibrinolysis===
*Plasminogen deficiency, dysfibrinogenemia, tissue plasminogen activator (tPA) deficiency, plasminogen activator inhibitor (PAI) increase, and factor XII deficiency impairs plasmin generation. <ref name="urlHypercoagulability - StatPearls - NCBI Bookshelf">{{cite web |url=https://www.ncbi.nlm.nih.gov/books/NBK538251/ |title=Hypercoagulability - StatPearls - NCBI Bookshelf |format= |work= |accessdate=}}</ref> 
*'''[[Familial_dysfibrinogenemia|Dysfibrinogenemia]]:''' The patients with structural or functional changes to fibrinogen result in dysfibrinogenemia through an abnormal thrombin-mediated conversion to fibrin and thereby, developing the risk for thrombosis or bleeding. Most patients are clinically asymptomatic inspite of having predisposition for bleeding, thrombosis or both.<ref name="pmid11900586">{{cite journal| author=Cunningham MT, Brandt JT, Laposata M, Olson JD| title=Laboratory diagnosis of dysfibrinogenemia. | journal=Arch Pathol Lab Med | year= 2002 | volume= 126 | issue= 4 | pages= 499-505 | pmid=11900586 | doi=10.1043/0003-9985(2002)126<0499:LDOD>2.0.CO;2 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11900586}} </ref>


*'''Antiphospholipid syndrome (APS):''' The most common acquired thrombophilia is the antiphospholipid syndrome (APS) in which antibodies are directed against natural constituents of cell membranes, the phospholipids. These antiphospholipid antibodies (APLA) occur in 3 to 5% of the population and may cause arterial or venous thrombosis and fetal loss. APLAs being tested for include lupus anticoagulant, anticardiolipin, anti-beta-2-glycoprotein. Lupus anticoagulant leads to prolongation of coagulation (aPTT) in vitro but thrombosis in vivo. Antiphospholipid antibodies may also occur secondary to other diseases (collagen vascular disease or infections) or drugs (phenytoin and cocaine among others). The most common thrombotic event is deep vein thrombosis. Any patient with stroke and rheumatological disorder should be screened for antiphospholipid antibody syndrome.  
===Antiphospholipid syndrome (APS) <ref name="pmid25025009">{{cite journal| author=Nakashima MO, Rogers HJ| title=Hypercoagulable states: an algorithmic approach to laboratory testing and update on monitoring of direct oral anticoagulants. | journal=Blood Res | year= 2014 | volume= 49 | issue= 2 | pages= 85-94 | pmid=25025009 | doi=10.5045/br.2014.49.2.85 | pmc=4090343 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25025009  }} </ref> <ref name="pmid11700155">{{cite journal| author=Thomas RH| title=Hypercoagulability syndromes. | journal=Arch Intern Med | year= 2001 | volume= 161 | issue= 20 | pages= 2433-9 | pmid=11700155 | doi=10.1001/archinte.161.20.2433 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11700155  }} </ref>===
*It is the most common acquired thrombophilia in which antibodies are directed against natural constituents of cell membranes, the phospholipids.  
*These antiphospholipid antibodies (APLA) consisting of '''lupus anticoagulant, anticardiolipin, and anti-beta-2-glycoprotein''' occur in 3 to 5% of the population and may cause arterial or venous thrombosis and fetal loss.  
*APLA may occur secondary to other diseases such as collagen vascular disease or infections or drugs like phenytoin.  
*Hence, any patient presenting with stroke, deep vein thrombosis, and rheumatological disorder should be screened for underlying antiphospholipid antibody syndrome.


*'''Malignancy:'''he second most common acquired hypercoagulability and leads to a prothrombotic state through the production of procoagulant factors (tissue factor and cancer procoagulant) and the interaction of tumor cells with blood and vascular endothelium. Stasis from tumor compression, paraproteinemia, and cytokine release pose an additional risk. In 85% of cancer patients, cancer procoagulant (CP) is elevated. This enzyme actives factor X thus causing hypercoagulability in cancer patients. Polycythemia vera poses a thrombotic risk in addition to hyperviscosity. Migratory thrombophlebitis as a consequence of visceral malignancy is known as Trousseau syndrome. The interaction of malignancy and coagulation is of interest as not only malignancy favors thrombosis but the hemostatic system influences angiogenesis which support tumor growth and spread. Targeting the hemostatic system might offer treatment options for anticancer therapy.   
===Malignancy===
* It is the second most common acquired hypercoagulability which leads to a prothrombotic state through the production of procoagulant factors (tissue factor and cancer procoagulant) and the interaction of tumor cells with blood and vascular endothelium further associated with vascular stasis from tumor compression, paraproteinemia, and cytokine release.
*In 85% cases, cancer procoagulant (CP) is elevated which activates factor X, and thus causing hypercoagulability in cancer patients. <ref name="pmid12407439">{{cite journal| author=Caine GJ, Stonelake PS, Lip GY, Kehoe ST| title=The hypercoagulable state of malignancy: pathogenesis and current debate. | journal=Neoplasia | year= 2002 | volume= 4 | issue= 6 | pages= 465-73 | pmid=12407439 | doi=10.1038/sj.neo.7900263 | pmc=1550339 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12407439  }} </ref>
*Migratory thrombophlebitis known as '''Trousseau syndrome''' and '''Polycythemia vera''' poses a thrombotic risk in addition to hyperviscosity. <ref name="pmid15806273">{{cite journal| author=Johnson CM, Mureebe L, Silver D| title=Hypercoagulable states: a review. | journal=Vasc Endovascular Surg | year= 2005 | volume= 39 | issue= 2 | pages= 123-33 | pmid=15806273 | doi=10.1177/153857440503900201 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15806273  }} </ref> 
*The interaction of malignancy and coagulation not only favors thrombosis but also the hemostatic system which influences angiogenesis and support tumor growth and spread. Hence, targeting the hemostatic system might offer treatment options for anticancer therapy. <ref name="pmid14675077">{{cite journal| author=Khorana AA| title=Malignancy, thrombosis and Trousseau: the case for an eponym. | journal=J Thromb Haemost | year= 2003 | volume= 1 | issue= 12 | pages= 2463-5 | pmid=14675077 | doi=10.1111/j.1538-7836.2003.00501.x | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14675077  }} </ref> <ref name="pmid6407544">{{cite journal| author=Rickles FR, Edwards RL| title=Activation of blood coagulation in cancer: Trousseau's syndrome revisited. | journal=Blood | year= 1983 | volume= 62 | issue= 1 | pages= 14-31 | pmid=6407544 | doi= | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=6407544  }} </ref> <ref name="pmid23889169">{{cite journal| author=Lima LG, Monteiro RQ| title=Activation of blood coagulation in cancer: implications for tumour progression. | journal=Biosci Rep | year= 2013 | volume= 33 | issue= 5 | pages=  | pmid=23889169 | doi=10.1042/BSR20130057 | pmc=3763425 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23889169 }} </ref>


*'''Smoking:''' Arterial bypass grafts fail prematurely in smokers. Smoking tobacco contains various toxins. Nicotine results in endothelial cell damage. The release of tissue plasminogen activator (tPA) and tissue factor pathway inhibitor (TFPI) get reduced. Carbon monoxide increases the permeability of endothelium to lipids thus leading to atheroma formation.
===Smoking===
*Smoking tobacco contains various toxins such as '''nicotine''' which results in '''endothelial cell damage'''.  
*The release of tissue plasminogen activator (tPA) and tissue factor pathway inhibitor (TFPI) get reduced.
*Carbon monoxide increases the permeability of endothelium to lipids thus leading to '''atheroma formation'''. <ref name="pmid15806273">{{cite journal| author=Johnson CM, Mureebe L, Silver D| title=Hypercoagulable states: a review. | journal=Vasc Endovascular Surg | year= 2005 | volume= 39 | issue= 2 | pages= 123-33 | pmid=15806273 | doi=10.1177/153857440503900201 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15806273  }} </ref>
*Hence, arterial bypass grafts fail prematurely in smokers.


*'''Exercise:''' Exercise improves the cardiovascular risk profile, but observations of sudden cardiac death in some individuals led investigators to search for causes. Exercise influences coagulation, fibrinolysis, and platelet aggregation. Usually, this is kept in balance but in some individuals, the immediate postexercise period is characterized by a hypercoagulable state with an increase of factor eight (intrinsic pathway activation) and platelet activation. Older individuals carry more cardiovascular risk factors and are less well trained. Thus they are prone to suffer adverse effects from the temporary hypercoagulable state following exercise. In the Tromso study regular, moderate-intensity exercise did not significantly impact the risk for thrombosis.
===Exercise===
*Exercise influences coagulation, fibrinolysis, and platelet aggregation which is usually kept in balance; however, in some cases the '''immediate postexercise period''' is characterized by a hypercoagulable state with an increase of factor eight (intrinsic pathway activation) and platelet activation. <ref name="pmid25467962">{{cite journal| author=Posthuma JJ, van der Meijden PE, Ten Cate H, Spronk HM| title=Short- and Long-term exercise induced alterations in haemostasis: a review of the literature. | journal=Blood Rev | year= 2015 | volume= 29 | issue= 3 | pages= 171-8 | pmid=25467962 | doi=10.1016/j.blre.2014.10.005 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25467962  }} </ref> <ref name="pmid2315896">{{cite journal| author=Arai M, Yorifuji H, Ikematsu S, Nagasawa H, Fujimaki M, Fukutake K | display-authors=etal| title=Influences of strenuous exercise (triathlon) on blood coagulation and fibrinolytic system. | journal=Thromb Res | year= 1990 | volume= 57 | issue= 3 | pages= 465-71 | pmid=2315896 | doi=10.1016/0049-3848(90)90262-b | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=2315896  }} </ref> <ref name="pmid14514536">{{cite journal| author=Smith JE| title=Effects of strenuous exercise on haemostasis. | journal=Br J Sports Med | year= 2003 | volume= 37 | issue= 5 | pages= 433-5 | pmid=14514536 | doi=10.1136/bjsm.37.5.433 | pmc=1751362 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14514536  }} </ref>
*Although exercise improves the cardiovascular risk profile; but older individuals carry more cardiovascular risk factors and are less well trained. Thus, they are prone to suffer adverse effects from the '''temporary hypercoagulable state''' following exercise. <ref name="pmid3758037">{{cite journal| author=Röcker L, Drygas WK, Heyduck B| title=Blood platelet activation and increase in thrombin activity following a marathon race. | journal=Eur J Appl Physiol Occup Physiol | year= 1986 | volume= 55 | issue= 4 | pages= 374-80 | pmid=3758037 | doi=10.1007/BF00422736 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3758037  }} </ref>


*'''Pregnancy:''' Through the increase of procoagulants (diverse coagulation factors and the number of platelets) and the decrease of anticoagulants (PAI) in addition to stasis caused by compression of the gravid uterus, pregnancy presents a time of hypercoagulability extending 2 months into the postpartum period. This was under evaluation in the MEGA study and LMWH is being tested to prevent miscarriage in pregnant women with inherited thrombophilias in the ALIFE study. The physiological changes that occur during pregnancy are mainly responsible for the increased thrombogenicity of the peripartum period. A number of clotting factors including factor VII, factor VIII, Factor X, von Willebrand factor, and fibrinogen are elevated as a result of hormonal changes. At the same time, resistance to activated protein C increases in the second and third trimesters and the activity of protein S is decreased due to changes in the total protein S antigen level. There is also an increase in a number of inhibitors of the fibrinolytic pathway such as activatable fibrinolytic inhibitor (TAFI) and plasminogen activator inhibitor 1 and 2 (PAI-1 and PAI-2).In addition, the physical changes of pregnancy result in an increased thrombotic state. Increased pressure on the pelvic veins from the gravid uterus and decreased flow in the lower extremities result in increased stasis. Relative compression of the left iliac vein by the right iliac artery as it courses across the vessel leads to an increase of clots in the left iliac vein. Although stasis increases throughout the course of pregnancy and leg pain and swelling are more frequent during the third trimester, incidence of DVT is distributed relatively equally across trimesters. Concomitant diseases such as systemic lupus erythematousor sickle cell disease as well as other risk factors including obesity, decreased mobility, increased age, and smoking all increase the risk of thrombosis. It has been estimated that the women who are over 35 and pregnant have a 1.38- fold increased risk of having a clotting event during the peripartum period. Women who have had spontaneous clotting events in the past have an increased risk of developing a second event with an estimated rate of recurrence of 10.9% during pregnancy. Overall, both the physiologic and anatomic changes of pregnancy take several weeks to resolve after delivery, and the risk of thrombosis remains elevated (and indeed even elevated compared to pregnancy) until approximately 6 weeks postpartum.
===Pregnancy===
*The physiological changes that occur during pregnancy presents a time of hypercoagulability extending from 2 months of gestation into the postpartum period through the increase of procoagulants (diverse coagulation factors and the number of platelets) and the decrease of anticoagulants (PAI) in addition to stasis caused by compression of the gravid uterus.
*'''Hematological changes:''' A number of clotting factors including factor VII, factor VIII, Factor X, von Willebrand factor, and fibrinogen are elevated as a result of hormonal changes. At the same time, resistance to activated protein C increases in the second and third trimesters and the activity of protein S is decreased due to changes in the total protein S antigen level. There is also an increase in a number of inhibitors of the fibrinolytic pathway such as activatable fibrinolytic inhibitor (TAFI) and plasminogen activator inhibitor 1 and 2 (PAI-1 and PAI-2). <ref>K. A. Bremme, “Haemostatic changes in pregnancy,” Best Practice and Research, vol. 16, no. 2, pp. 153–168, 2003</ref> <ref name="pmid11943930">{{cite journal| author=Antovic A, Blombäck M, Bremme K, He S| title=The assay of overall haemostasis potential used to monitor the low molecular mass (weight) heparin, dalteparin, treatment in pregnant women with previous thromboembolism. | journal=Blood Coagul Fibrinolysis | year= 2002 | volume= 13 | issue= 3 | pages= 181-6 | pmid=11943930 | doi=10.1097/00001721-200204000-00002 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11943930  }} </ref> <ref name="pmid9175686">{{cite journal| author=Cerneca F, Ricci G, Simeone R, Malisano M, Alberico S, Guaschino S| title=Coagulation and fibrinolysis changes in normal pregnancy. Increased levels of procoagulants and reduced levels of inhibitors during pregnancy induce a hypercoagulable state, combined with a reactive fibrinolysis. | journal=Eur J Obstet Gynecol Reprod Biol | year= 1997 | volume= 73 | issue= 1 | pages= 31-6 | pmid=9175686 | doi=10.1016/s0301-2115(97)02734-6 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=9175686  }} </ref>
*'''Physical changes:''' An increased pressure on the pelvic veins from the gravid uterus and decreased flow in the lower extremities result in increased stasis and thrombotic state. Relative compression of the left iliac vein by the right iliac artery as it courses across the vessel leads to an increase of clots in the left iliac vein. Although stasis increases throughout the course of pregnancy and leg pain and swelling are more frequent during the third trimester, incidence of DVT is distributed relatively equally across trimesters. <ref name="GoldhaberTapson2004">{{cite journal|last1=Goldhaber|first1=Samuel Z.|last2=Tapson|first2=Victor F.|title=A prospective registry of 5,451 patients with ultrasound-confirmed deep vein thrombosis|journal=The American Journal of Cardiology|volume=93|issue=2|year=2004|pages=259–262|issn=00029149|doi=10.1016/j.amjcard.2003.09.057}}</ref> <ref name="MacklonGreer1997">{{cite journal|last1=Macklon|first1=Nicholas S.|last2=Greer|first2=Ian A.|title=The deep venous system in the puerperium: an ultrasound study|journal=BJOG: An International Journal of Obstetrics and Gynaecology|volume=104|issue=2|year=1997|pages=198–200|issn=1470-0328|doi=10.1111/j.1471-0528.1997.tb11044.x}}</ref> <ref name="James2009">{{cite journal|last1=James|first1=Andra H.|title=Venous Thromboembolism in Pregnancy|journal=Arteriosclerosis, Thrombosis, and Vascular Biology|volume=29|issue=3|year=2009|pages=326–331|issn=1079-5642|doi=10.1161/ATVBAHA.109.184127}}</ref>
*'''Concomitant diseases''' such as systemic lupus erythematous or sickle cell disease along other risk factors including obesity, decreased mobility, increased age, and smoking further elevates the thrombosis risk.  
*'''Predisposing factors:''' It has been observed that the pregnant women over 35yrs of age have a 1.38 fold increased risk of having a clotting event during the peripartum period. Additionally, women who have had spontaneous clotting events in the past have an increased risk of developing a second event with an estimated rate of recurrence of 10.9% during pregnancy. <ref name="pmid16647915">{{cite journal| author=James AH, Jamison MG, Brancazio LR, Myers ER| title=Venous thromboembolism during pregnancy and the postpartum period: incidence, risk factors, and mortality. | journal=Am J Obstet Gynecol | year= 2006 | volume= 194 | issue= 5 | pages= 1311-5 | pmid=16647915 | doi=10.1016/j.ajog.2005.11.008 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16647915  }} </ref> <ref name="PabingerGrafenhofer2002">{{cite journal|last1=Pabinger|first1=Ingrid|last2=Grafenhofer|first2=Helga|last3=Kyrle|first3=Paul A.|last4=Quehenberger|first4=Peter|last5=Mannhalter|first5=Christine|last6=Lechner|first6=Klaus|last7=Kaider|first7=Alexandra|title=Temporary increase in the risk for recurrence during pregnancy in women with a history of venous thromboembolism|journal=Blood|volume=100|issue=3|year=2002|pages=1060–1062|issn=1528-0020|doi=10.1182/blood-2002-01-0149}}</ref>
*Overall, both the physiologic and anatomic changes of pregnancy take several weeks to resolve after delivery, and the risk of thrombosis remains elevated compared to pregnancy until approximately 6 weeks postpartum. <ref name="pmid16287790">{{cite journal| author=Heit JA, Kobbervig CE, James AH, Petterson TM, Bailey KR, Melton LJ| title=Trends in the incidence of venous thromboembolism during pregnancy or postpartum: a 30-year population-based study. | journal=Ann Intern Med | year= 2005 | volume= 143 | issue= 10 | pages= 697-706 | pmid=16287790 | doi=10.7326/0003-4819-143-10-200511150-00006 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16287790  }} </ref>


*'''Heparin-induced thrombocytopenia (HIT):'''Heparin is a commonly used anticoagulant. Under certain circumstances, arterial and venous thrombosis concomitantly with thrombocytopenia paradoxically results from prolonged heparin administration, which is called heparin-induced thrombocytopenia (HIT). In type-I HIT platelets show a weak reduction of platelets and have little clinical consequences. This is in contrast to the strong reduction of thrombocytes and serious sequelae of HIT type-II. The conformational change of heparin following heparin binding to platelet factor 4 triggers antibody production to heparin. Subsequently, monocytes become activated and attack the vascular endothelium leading to thrombotic events.
===Heparin-induced thrombocytopenia (HIT) <ref name="urlHypercoagulability - StatPearls - NCBI Bookshelf">{{cite web |url=https://www.ncbi.nlm.nih.gov/books/NBK538251/ |title=Hypercoagulability - StatPearls - NCBI Bookshelf |format= |work= |accessdate=}}</ref>===
*'''Heparin''' is a commonly used anticoagulant and under certain circumstances, arterial and venous thrombosis concomitantly with thrombocytopenia paradoxically results from its prolonged administration which is called heparin-induced thrombocytopenia (HIT). The conformational change of heparin following heparin binding to platelet factor 4 triggers antibody production to heparin. Subsequently, monocytes become activated and attack the vascular endothelium leading to thrombotic events. <ref name="pmid15806273">{{cite journal| author=Johnson CM, Mureebe L, Silver D| title=Hypercoagulable states: a review. | journal=Vasc Endovascular Surg | year= 2005 | volume= 39 | issue= 2 | pages= 123-33 | pmid=15806273 | doi=10.1177/153857440503900201 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15806273  }} </ref>
*'''Type-I HIT:''' Platelets show a weak reduction and have little clinical consequences.
*'''Type-II HIT:''' It characterizes the strong reduction of thrombocytes and serious clinical sequelae.


*'''Trauma:'''Trauma is another acquired hypercoagulable state. Procoagulant disbalance is more pronounced during the first 24 hours following injury and in women. The onset of respiratory distress syndrome and multiorgan failure following trauma has been associated with elevated tissue factor.
===Trauma <ref name="urlHypercoagulability - StatPearls - NCBI Bookshelf">{{cite web |url=https://www.ncbi.nlm.nih.gov/books/NBK538251/ |title=Hypercoagulability - StatPearls - NCBI Bookshelf |format= |work= |accessdate=}}</ref>===
*Trauma causes the '''procoagulant disbalance''' which is more pronounced during the '''first 24 hours''' following injury and in women.  
*The onset of respiratory distress syndrome and multiorgan failure following trauma has been correlated with elevated tissue factor. <ref name="pmid15761339">{{cite journal| author=Schreiber MA, Differding J, Thorborg P, Mayberry JC, Mullins RJ| title=Hypercoagulability is most prevalent early after injury and in female patients. | journal=J Trauma | year= 2005 | volume= 58 | issue= 3 | pages= 475-80; discussion 480-1 | pmid=15761339 | doi=10.1097/01.ta.0000153938.77777.26 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15761339  }} </ref>


*'''Inflammatory and hypercoagulable state:''' There is an interplay between inflammation and the coagulation system. Inflammation triggers a hypercoagulable state. Endotoxin activates the complement system leading to thrombocytopenia and hypercoagulability. The relation between inflammation and coagulation can be observed clinically in patients with purpura, vasculitis, and septic thromboembolism. Coagulation helps to limit the expansion of infection, and some bacteria use fibrinolytic properties to oppose this response. Autoimmune diseases like systemic lupus erythematosus, immune thrombocytopenic purpura, polyarteritis nodosa, polymyositis, dermatomyositis, inflammatory bowel disease, and Behcet's syndrome increase the risk of thrombotic events. The cytomegaly virus (CMV) has correlations to atherogenesis through a change of the cellular lipid metabolism and leukocyte adherence. Other conditions associated with a hypercoagulable state include myeloproliferative disorders, multiple myeloma, paroxysmal nocturnal hemoglobinuria, heart failure. The endothelium of the left atrial appendage showed higher expression of tissue factor and plasminogen activator inhibitor compared to the right atrial appendage. This inherent prothrombotic property of the LAA in addition to flow disturbances of atrial fibrillation leads to thromboembolic events.
===Inflammatory and hypercoagulable state===
*There is an interplay between inflammation and the coagulation system as inflammation triggers a hypercoagulable state which can be observed clinically in patients with purpura, vasculitis, and septic thromboembolism. <ref name="pmid25883536">{{cite journal| author=Emmi G, Silvestri E, Squatrito D, Amedei A, Niccolai E, D'Elios MM | display-authors=etal| title=Thrombosis in vasculitis: from pathogenesis to treatment. | journal=Thromb J | year= 2015 | volume= 13 | issue=  | pages= 15 | pmid=25883536 | doi=10.1186/s12959-015-0047-z | pmc=4399148 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25883536  }} </ref>
*'''Endotoxin''' activates the complement system leading to thrombocytopenia and hypercoagulability. Moreover, coagulation helps to limit the expansion of infection and some bacteria use fibrinolytic properties to oppose this response. The cytomegaly virus (CMV) has correlations to atherogenesis through a change of the cellular lipid metabolism and leukocyte adherence. <ref name="pmid4683877">{{cite journal| author=Kane MA, May JE, Frank MM| title=Interactions of the classical and alternate complement pathway with endotoxin lipopolysaccharide. Effect on platelets and blood coagulation. | journal=J Clin Invest | year= 1973 | volume= 52 | issue= 2 | pages= 370-6 | pmid=4683877 | doi=10.1172/JCI107193 | pmc=302266 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=4683877  }} </ref> <ref name="pmid9327777">{{cite journal| author=Nieto FJ, Sorlie P, Comstock GW, Wu K, Adam E, Melnick JL | display-authors=etal| title=Cytomegalovirus infection, lipoprotein(a), and hypercoagulability: an atherogenic link? | journal=Arterioscler Thromb Vasc Biol | year= 1997 | volume= 17 | issue= 9 | pages= 1780-5 | pmid=9327777 | doi=10.1161/01.atv.17.9.1780 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=9327777  }} </ref>
*'''Autoimmune diseases''' like systemic lupus erythematosus, immune thrombocytopenic purpura, polyarteritis nodosa, polymyositis, dermatomyositis, inflammatory bowel disease, and Behcet's syndrome increase the risk of thrombotic events. Other conditions associated with a hypercoagulable state include myeloproliferative disorders, multiple myeloma, paroxysmal nocturnal hemoglobinuria, heart failure. <ref name="pmid25750012">{{cite journal| author=Tamaki H, Khasnis A| title=Venous thromboembolism in systemic autoimmune diseases: A narrative review with emphasis on primary systemic vasculitides. | journal=Vasc Med | year= 2015 | volume= 20 | issue= 4 | pages= 369-76 | pmid=25750012 | doi=10.1177/1358863X15573838 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25750012  }} </ref><ref name="pmid16247748">{{cite journal| author=Kravitz MS, Shoenfeld Y| title=Thrombocytopenic conditions-autoimmunity and hypercoagulability: commonalities and differences in ITP, TTP, HIT, and APS. | journal=Am J Hematol | year= 2005 | volume= 80 | issue= 3 | pages= 232-42 | pmid=16247748 | doi=10.1002/ajh.20408 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16247748  }} </ref> <ref name="pmid22937487">{{cite journal| author=Zöller B, Li X, Sundquist J, Sundquist K| title=Autoimmune diseases and venous thromboembolism: a review of the literature. | journal=Am J Cardiovasc Dis | year= 2012 | volume= 2 | issue= 3 | pages= 171-83 | pmid=22937487 | doi= | pmc=3427982 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=22937487  }} </ref> <ref name="pmid21239832">{{cite journal| author=Kristinsson SY| title=Thrombosis in multiple myeloma. | journal=Hematology Am Soc Hematol Educ Program | year= 2010 | volume= 2010 | issue=  | pages= 437-44 | pmid=21239832 | doi=10.1182/asheducation-2010.1.437 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=21239832  }} </ref> <ref name="pmid10193748">{{cite journal| author=Lip GY, Gibbs CR| title=Does heart failure confer a hypercoagulable state? Virchow's triad revisited. | journal=J Am Coll Cardiol | year= 1999 | volume= 33 | issue= 5 | pages= 1424-6 | pmid=10193748 | doi=10.1016/s0735-1097(99)00033-9 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10193748  }} </ref>
*'''Cardiac events:''' The endothelium of the left atrial appendage (LAA) showed higher expression of tissue factor and plasminogen activator inhibitor compared to the right atrial appendage. This inherent prothrombotic property of the LAA in addition to flow disturbances of atrial fibrillation leads to thromboembolic events.<ref name="pmid25814212">{{cite journal| author=Breitenstein A, Glanzmann M, Falk V, Maisano F, Stämpfli SF, Holy EW | display-authors=etal| title=Increased prothrombotic profile in the left atrial appendage of atrial fibrillation patients. | journal=Int J Cardiol | year= 2015 | volume= 185 | issue=  | pages= 250-5 | pmid=25814212 | doi=10.1016/j.ijcard.2015.03.092 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=25814212  }} </ref>


==References==
==References==

Latest revision as of 18:48, 6 April 2021

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Asiri Ediriwickrema, M.D., M.H.S. [2] Jaspinder Kaur, MBBS[3]

Overview

The pathogenesis of thrombophilia is multi-factorial. It is characterized by hypercoagulability, which by itself or in synergy with endothelial injury or stasis (Virchow's Triad) can predispose to clot formation. Multiple genetic mutations and predisposing conditions have been associated with the increased risk of thrombosis due to abnormalities in the coagulation cascade.[1] The most common genes involved in the pathogenesis of acquired thrombophilias are Factor V Leiden and prothrombin gene mutations.

Pathophysiology

  • Coagulation is an inherent property of the hematologic system and normal blood flow is maintained by the balance between the pro-coagulant and anti-thrombotic factors under healthy conditions. A hypercoagulable state and subsequent thromboembolism is a result of overactivity of pro-coagulant factors or a deficiency in anti-coagulants. Anticoagulants that regulate thrombin include antithrombin, protein C, and protein S. The primary mechanism for thrombus formation in common inherited thrombophilic states involves thrombin dysregulation. However, the interplay of these factors is complicated process consisting of coagulation activators and inhibitors and their production and degradation (quantitative) and functional properties (qualitative) influencing the thrombosis process.
Thrombus formation in inherited thrombophilia. In thrombophilia, procoagulant and anticoagulant factors are dysregulated leading to thrombus formation

Figure 1: Thrombus formation in inherited thrombophilias. Adapted from: N Engl J Med. 2001 Apr 19;344(16):1222-31.[1]

Antithrombin III (ATIII) deficiency

  • Antithrombin (previously called antithrombin III) is synthesized by the liver but is not vitamin K-dependent. Its inhibitory effect is not confined to thrombin. It also inhibits the activated clotting factors IXa, Xa, XIa, XIIa and tissue factor-bound factor VIIa. Antithrombin III binds to heparin on endothelial cells and forms a complex between antithrombin and the serine proteases and thus, inhibiting coagulation. Mutations in antithrombin can lead to increased thrombus formation. [2] [3]
  • The prevalence may be 1 in 500 in the general population. Affected patients have antithrombin levels 40–60% of normal, and 70% of those affected experience thrombo-embolic events before the age of 50. Thrombotic episodes are rare before puberty in AT-deficient individuals. They start to occur with some frequency after puberty, with the risk increasing substantially with advancing age. [4] [5]
  • Type of inheritance: Antithrombin (AT) deficiency is a heterogeneous disorder. It is usually inherited in an autosomal dominant fashion, thereby affecting both sexes equally. Homozygous ATIII deficiency is incompatible with life unless affecting the heparin-binding site. [6]
  • Causes: ATIII deficiency can occur as a consequence of reduced synthesis (liver damage) or increased loss (nephrotic syndrome, enteropathy, DIC, sepsis, burn, trauma, microangiopathy, and cardiopulmonary bypass surgery). Usually these patients present with venous thrombosis and less likely with arterial thrombosis. [7]
  • Classification: Three major types of heritable AT deficiency are recognized as follows: [3]
    • Type I: It is characterized by a quantitative reduction of qualitatively (functionally) normal antithrombin protein and thereby reducing both the antigenic and functional activity of AT in the blood. The values are reduced by approximately 50 percent in the heterozygote. The 1997 antithrombin mutation database included 80 distinct mutations in patients with type I deficiency. The database shows that the molecular basis for this disorder is usually a small deletion or insertion (less than 22 base pairs) or a deletion of a major segment of the AT gene. [8] [9]
    • Type II: It is produced by a discrete molecular qualitative mutational defect within the protein which either affect the heparin-binding site (HBS), the reactive site (RS) or result in pleiotropic effects (PE). While the AT immunologic activity is normal in this deficiency, plasma AT functional activity is markedly reduced leading to risk of thrombosis. It is subclassified according to the site of the molecular defect: [6] [10]
      • Reactive site (RS) and abnormalities residing in the reactive (thrombin binding) site.
      • Heparin binding site (HBS) and abnormalities residing in the heparin binding site.
      • Pleiotropic effect (PE) and abnormalities residing in both reactive and heparin binding sites.
    • Type III: This type is characterized by normal functional and antigenic antithrombin levels but impaired interaction between AT and heparin. [11]

Protein C deficiency

  • Protein C is a vitamin K-dependent protease synthesized in the liver and circulates in plasma at low concentrations which serves a critical role in the regulation of thrombin. Protein C becomes activated to form activated protein C (APC) via interactions with thrombin. APC acts as one of the major inhibitors of the coagulation system by cleaving and inactivating clotting factors V and VIII which are necessary for efficient thrombin generation, and thereby exerting potent anticoagulant activity. Moreover, APC also reduces platelet prothrombinase activity by degrading platelet bound factor Va at the receptor for factor Xa. Additionally, the inhibitory effects of APC are facilitated through the cofactor activity of protein S, another vitamin K-dependent protein. [3][12]
  • Protein C deficiency is a rare acquired or congenital disorder characterized by a reduction in the activity of protein C, a plasma serine protease involved in the regulation of blood coagulation which results in the excessive formation of blood clots (thrombophilia).
  • Congenital protein C deficiency results from mutations in the PROC gene and inherited in an autosomal dominant manner. The gene for protein C is located on chromosome 2 (2q13–14) and appears to be closely related to the gene for factor IX. [13]
  • Mode of inheritance: [14]
    • Heterozygous: Mutations in a single copy in heterozygous individuals cause mild protein C deficiency.
    • Homozygous: Individuals with homozygous mutations present with severe protein C deficiency and thrombotic tendency in infancy characterized as purpura fulminans. [15]
  • Inherited: Two major subtypes of heterozygous protein C deficiency have been delineated using immunologic and functional assays. Over 160 different gene abnormalities have been associated with the two subtypes.[14] [16]
    • Type I: This state is more common with a reduced plasma protein C concentration at approximately 50% of normal in both immunologic and functional assays. Most affected patients are heterozygous and carries an increased risk of developing warfarin-induced skin necrosis. More than half of the mutations are missense and nonsense mutations and other includes promoter mutations, splice site mutations, in-frame deletions, frameshift deletions, in-frame insertions, and frameshift insertions. Moreover, there is marked phenotypic variability among patients with heterozygous type I protein C deficiency. Similar mutations have been found among symptomatic and asymptomatic individuals which suggests that the nature of the protein C gene defect alone does not explain the phenotypic variability. [16] [17]
    • Type II: It has normal plasma protein C antigen levels with decreased functional activity; and a variety of different point mutations affecting protein function have been identified in this disorder. [16]
  • Acquired: Protein C is known to have a role in the regulation of inflammation and sepsis which demonstrates its cytoprotective functions. Reduced protein C activity is observed in DIC, liver disease, coumarins use, and adverse pregnancy outcomes such as DVT, preeclampsia, intrauterine growth restriction and recurrent pregnancy loss. [12] [18]
  • Additionally, the half-life of protein C is shorter than the half-life of other vitamin K-dependent coagulation factors; hence, the risk of increased coagulation with the initiation of vitamin K antagonists can be seen; and thereby need the bridging with parenteral heparin to avoid warfarin-induced skin necrosis.

Protein S deficiency [19]

  • Protein S is a vitamin K-dependent protease that circulates in plasma at low concentrations and serves a crucial role in the regulation of coagulation.
  • In circulation, approximately 40% of protein S is free, remains uncomplexed and is the active moiety; while about 60% is in a high-affinity complex with the complement regulatory factor C4b-binding protein (C4BP) and has no cofactor activity. The bioavailability of protein S is closely linked to the concentration of C4bBP, which acts as an important regulatory protein in the activated protein C:protein S inhibitory pathway. [20]
  • The anticoagulant activity of protein S is two-fold as follows: [21]
    • Protein S operates as a cofactor for activated protein C (APC) and inactivates coagulation Factor Va and Factor VIIIa;
    • Protein S is also a cofactor for the tissue factor pathway inhibitor (TFPI) protein resulting in the inactivation of Factor Xa and tissue factor (TF)/Factor VIIa.
  • Protein S deficiency is usually congenital caused by mutations in the PROS1 gene and mainly an autosomal dominant pathology. [20]
  • Mode of inheritance:
    • Heterozygous: Mutations in a single copy in heterozygous individuals cause mild protein S deficiency
    • Homozygous: Individuals with homozygous mutations present with severe protein S deficiency
  • Inherited: More than 200 PROS mutations have been described and may result in three different forms of protein S deficiency: [20]
    • Type I: It is a quantitative defect presenting with low levels of total protein S (TPS) and free protein S (FPS) with reduced levels of functional protein S activity. [22]
    • Type II (or Type IIb): This type of protein S deficiency is characterized by decreased functional protein S activity with normal levels of TPS and FPS antigens. Interestingly, all five mutations originally described were missense mutations located in the N-terminal end of the protein S molecule consisting of the domains that interact with activated protein C. [23]
    • Type III (or Type IIa): It consists of a quantitative defect presenting with normal levels of TPS, but selectively reduced levels of FPS and functional protein S activity to less than approximately 40 percent of normal. [24]
  • Acquired: Causes of temporary acquired fluctuations in protein S levels may include vitamin K-antagonist therapy (coumarins), antiphospholipid antibodies, chronic infections, severe hepatic disease, nephritic syndrome, and DIC. [25]
  • Gender predilection: Protein S levels are slightly higher in men than in women. Contrarily, protein S levels fall progressively during pregnancy and are reduced to a lesser extent in women using oestrogen containing oral contraceptives or hormone replacement therapy. Moreover, the risk of VTE is also increased in patients using oral contraceptives and pregnancy. [1] [26]

Factor V Leiden mutation

  • The most common inherited thrombophilia is Factor V Leiden which is a polymorphism of Factor V that is resistant to APC inactivation. Other FV mutations include factor V Cambridge and factor V Hong Kong. [1] [10] [27]
  • Activated protein C (APC): Protein C interacts with thrombomodulin to become APC which has anticoagulant, anti-inflammatory, and cytoprotective properties. The signal cascade leading to APC can become distorted through many acquired or inherited mechanisms leading to APC resistance. Hence, APC resistance occurs when APC fails to inactivate downstream coagulation factors, specifically Factor V and Factor VIII. [7]
  • The factor V Leiden mutation further increases arterial thrombosis risk by enhancing thrombin production. Protein C and S are natural anticoagulants which inhibit thrombin formation. Dysregulation in APC can occur as either defects in the protein C or S molecule (Protein C and S deficiency) or as resistance to APC activity.[1] [6] [28]

Prothrombin G20210A mutation

  • Prothrombin (factor II) is the precursor to thrombin, the end-product of the coagulation cascade. Prothrombin has procoagulant, anticoagulant and antifibrinolytic activities and thus a disorder involving prothrombin results in multiple hemostasis imbalances.
  • It is the second most common inherited thrombophilia which involves a gain of function mutation of the prothrombin gene (Prothrombin G20210A) resulting in increased protein activity and thrombus formation. [10] [27] [29]
  • It is due to a single point mutation which involves the G to A transition at nucleotide 20210 in the 30-untranslated region of the prothrombin gene and thereby associated with elevated plasma prothrombin levels and demonstrating a higher risk for arterial and venous thrombotic events. [29]

Hyperhomocysteinemia

  • Homocystinuria and hyperhomocysteinemia are rare metabolism disorder associated with the marked elevations of plasma and urine homocysteine concentrations resulting from an impaired intracellular metabolism of homocysteine which can be due to both genetic and acquired abnormality.
  • Homocysteine is an amino acid derived from methionine which is metabolized by the body in two possible following pathways: [30]
    • Transsulfuration of homocysteine produces cysteine, and this reaction is catalyzed by cystathionine-β-synthase which requires pyridoxal phosphate (Vitamin B) as a cofactor.
    • Remethylation of homocysteine produces methionine which is catalyzed either by methionine synthase or by betaine homocysteine methyltransferase. Vitamin B12 (cobalamin) is the precursor of methylcobalamin, which is the cofactor for methionine synthase.
  • Nutritional deficiencies in vitamin cofactors such as vitamin B6, B12, and folate or genetic defects of enzymes such as cystathionine beta-synthase (CBS) or methylenetetrahydrofolate reductase (MTHFR) decrease the efficiency of homocysteine metabolism. Furthermore, chronic medical conditions such as renal failure, hypothyroidism, and drugs such as methotrexate, phenytoin, and carbamazepine increase homocysteine levels. [6] [10] [27]
  • Hence, premature atherosclerosis and arterial thrombosis is associated with severe hyperhomocysteinemia.

Elevated factor VIII (FVIII)[6] [7]

  • Higher levels: African-Americans appear to have its higher levels. It further increases the risk of thrombosis, and found to be correlated with acute phase reactions, estrogen usage, pregnancy, and aerobic exercise.
  • Lower levels: Individuals with blood group "O" tend to have lower levels of FVIII and correlated with bleeding in hemophilia A patients.

Dysfibrinolysis

  • Plasminogen deficiency, dysfibrinogenemia, tissue plasminogen activator (tPA) deficiency, plasminogen activator inhibitor (PAI) increase, and factor XII deficiency impairs plasmin generation. [4]
  • Dysfibrinogenemia: The patients with structural or functional changes to fibrinogen result in dysfibrinogenemia through an abnormal thrombin-mediated conversion to fibrin and thereby, developing the risk for thrombosis or bleeding. Most patients are clinically asymptomatic inspite of having predisposition for bleeding, thrombosis or both.[31]

Antiphospholipid syndrome (APS) [7] [32]

  • It is the most common acquired thrombophilia in which antibodies are directed against natural constituents of cell membranes, the phospholipids.
  • These antiphospholipid antibodies (APLA) consisting of lupus anticoagulant, anticardiolipin, and anti-beta-2-glycoprotein occur in 3 to 5% of the population and may cause arterial or venous thrombosis and fetal loss.
  • APLA may occur secondary to other diseases such as collagen vascular disease or infections or drugs like phenytoin.
  • Hence, any patient presenting with stroke, deep vein thrombosis, and rheumatological disorder should be screened for underlying antiphospholipid antibody syndrome.

Malignancy

  • It is the second most common acquired hypercoagulability which leads to a prothrombotic state through the production of procoagulant factors (tissue factor and cancer procoagulant) and the interaction of tumor cells with blood and vascular endothelium further associated with vascular stasis from tumor compression, paraproteinemia, and cytokine release.
  • In 85% cases, cancer procoagulant (CP) is elevated which activates factor X, and thus causing hypercoagulability in cancer patients. [33]
  • Migratory thrombophlebitis known as Trousseau syndrome and Polycythemia vera poses a thrombotic risk in addition to hyperviscosity. [10]
  • The interaction of malignancy and coagulation not only favors thrombosis but also the hemostatic system which influences angiogenesis and support tumor growth and spread. Hence, targeting the hemostatic system might offer treatment options for anticancer therapy. [34] [35] [36]

Smoking

  • Smoking tobacco contains various toxins such as nicotine which results in endothelial cell damage.
  • The release of tissue plasminogen activator (tPA) and tissue factor pathway inhibitor (TFPI) get reduced.
  • Carbon monoxide increases the permeability of endothelium to lipids thus leading to atheroma formation. [10]
  • Hence, arterial bypass grafts fail prematurely in smokers.

Exercise

  • Exercise influences coagulation, fibrinolysis, and platelet aggregation which is usually kept in balance; however, in some cases the immediate postexercise period is characterized by a hypercoagulable state with an increase of factor eight (intrinsic pathway activation) and platelet activation. [37] [38] [39]
  • Although exercise improves the cardiovascular risk profile; but older individuals carry more cardiovascular risk factors and are less well trained. Thus, they are prone to suffer adverse effects from the temporary hypercoagulable state following exercise. [40]

Pregnancy

  • The physiological changes that occur during pregnancy presents a time of hypercoagulability extending from 2 months of gestation into the postpartum period through the increase of procoagulants (diverse coagulation factors and the number of platelets) and the decrease of anticoagulants (PAI) in addition to stasis caused by compression of the gravid uterus.
  • Hematological changes: A number of clotting factors including factor VII, factor VIII, Factor X, von Willebrand factor, and fibrinogen are elevated as a result of hormonal changes. At the same time, resistance to activated protein C increases in the second and third trimesters and the activity of protein S is decreased due to changes in the total protein S antigen level. There is also an increase in a number of inhibitors of the fibrinolytic pathway such as activatable fibrinolytic inhibitor (TAFI) and plasminogen activator inhibitor 1 and 2 (PAI-1 and PAI-2). [41] [42] [43]
  • Physical changes: An increased pressure on the pelvic veins from the gravid uterus and decreased flow in the lower extremities result in increased stasis and thrombotic state. Relative compression of the left iliac vein by the right iliac artery as it courses across the vessel leads to an increase of clots in the left iliac vein. Although stasis increases throughout the course of pregnancy and leg pain and swelling are more frequent during the third trimester, incidence of DVT is distributed relatively equally across trimesters. [44] [45] [46]
  • Concomitant diseases such as systemic lupus erythematous or sickle cell disease along other risk factors including obesity, decreased mobility, increased age, and smoking further elevates the thrombosis risk.
  • Predisposing factors: It has been observed that the pregnant women over 35yrs of age have a 1.38 fold increased risk of having a clotting event during the peripartum period. Additionally, women who have had spontaneous clotting events in the past have an increased risk of developing a second event with an estimated rate of recurrence of 10.9% during pregnancy. [47] [48]
  • Overall, both the physiologic and anatomic changes of pregnancy take several weeks to resolve after delivery, and the risk of thrombosis remains elevated compared to pregnancy until approximately 6 weeks postpartum. [49]

Heparin-induced thrombocytopenia (HIT) [4]

  • Heparin is a commonly used anticoagulant and under certain circumstances, arterial and venous thrombosis concomitantly with thrombocytopenia paradoxically results from its prolonged administration which is called heparin-induced thrombocytopenia (HIT). The conformational change of heparin following heparin binding to platelet factor 4 triggers antibody production to heparin. Subsequently, monocytes become activated and attack the vascular endothelium leading to thrombotic events. [10]
  • Type-I HIT: Platelets show a weak reduction and have little clinical consequences.
  • Type-II HIT: It characterizes the strong reduction of thrombocytes and serious clinical sequelae.

Trauma [4]

  • Trauma causes the procoagulant disbalance which is more pronounced during the first 24 hours following injury and in women.
  • The onset of respiratory distress syndrome and multiorgan failure following trauma has been correlated with elevated tissue factor. [50]

Inflammatory and hypercoagulable state

  • There is an interplay between inflammation and the coagulation system as inflammation triggers a hypercoagulable state which can be observed clinically in patients with purpura, vasculitis, and septic thromboembolism. [51]
  • Endotoxin activates the complement system leading to thrombocytopenia and hypercoagulability. Moreover, coagulation helps to limit the expansion of infection and some bacteria use fibrinolytic properties to oppose this response. The cytomegaly virus (CMV) has correlations to atherogenesis through a change of the cellular lipid metabolism and leukocyte adherence. [52] [53]
  • Autoimmune diseases like systemic lupus erythematosus, immune thrombocytopenic purpura, polyarteritis nodosa, polymyositis, dermatomyositis, inflammatory bowel disease, and Behcet's syndrome increase the risk of thrombotic events. Other conditions associated with a hypercoagulable state include myeloproliferative disorders, multiple myeloma, paroxysmal nocturnal hemoglobinuria, heart failure. [54][55] [56] [57] [58]
  • Cardiac events: The endothelium of the left atrial appendage (LAA) showed higher expression of tissue factor and plasminogen activator inhibitor compared to the right atrial appendage. This inherent prothrombotic property of the LAA in addition to flow disturbances of atrial fibrillation leads to thromboembolic events.[59]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Seligsohn U, Lubetsky A (2001). "Genetic susceptibility to venous thrombosis". N Engl J Med. 344 (16): 1222–31. doi:10.1056/NEJM200104193441607. PMID 11309638.
  2. ↑ EGEBERG O (1965). "INHERITED ANTITHROMBIN DEFICIENCY CAUSING THROMBOPHILIA". Thromb Diath Haemorrh. 13: 516–30. PMID 14347873.
  3. ↑ 3.0 3.1 3.2 Walker, Isobel D; Greaves, M; Preston, F. E (2001). "Investigation and management of heritable thrombophilia". British Journal of Haematology. 114 (3): 512–528. doi:10.1046/j.1365-2141.2001.02981.x. ISSN 0007-1048.
  4. ↑ 4.0 4.1 4.2 4.3 "Hypercoagulability - StatPearls - NCBI Bookshelf".
  5. ↑ Thaler E, Lechner K (1981). "Antithrombin III deficiency and thromboembolism". Clin Haematol. 10 (2): 369–90. PMID 7032781.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 März W, Nauck M, Wieland H (2000). "The molecular mechanisms of inherited thrombophilia". Z Kardiol. 89 (7): 575–86. doi:10.1007/s003920070206. PMID 10957782.
  7. ↑ 7.0 7.1 7.2 7.3 Nakashima MO, Rogers HJ (2014). "Hypercoagulable states: an algorithmic approach to laboratory testing and update on monitoring of direct oral anticoagulants". Blood Res. 49 (2): 85–94. doi:10.5045/br.2014.49.2.85. PMC 4090343. PMID 25025009.
  8. ↑ Ambruso DR, Leonard BD, Bies RD, Jacobson L, Hathaway WE, Reeve EB (1982). "Antithrombin III deficiency: decreased synthesis of a biochemically normal molecule". Blood. 60 (1): 78–83. PMID 7082848.
  9. ↑ Lane DA, Bayston T, Olds RJ, Fitches AC, Cooper DN, Millar DS; et al. (1997). "Antithrombin mutation database: 2nd (1997) update. For the Plasma Coagulation Inhibitors Subcommittee of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis". Thromb Haemost. 77 (1): 197–211. PMID 9031473.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 Johnson CM, Mureebe L, Silver D (2005). "Hypercoagulable states: a review". Vasc Endovascular Surg. 39 (2): 123–33. doi:10.1177/153857440503900201. PMID 15806273.
  11. ↑ Tait RC, Walker ID, Perry DJ, Islam SI, Daly ME, McCall F; et al. (1994). "Prevalence of antithrombin deficiency in the healthy population". Br J Haematol. 87 (1): 106–12. doi:10.1111/j.1365-2141.1994.tb04878.x. PMID 7947234.
  12. ↑ 12.0 12.1 Mosnier LO, Zlokovic BV, Griffin JH (2007). "The cytoprotective protein C pathway". Blood. 109 (8): 3161–72. doi:10.1182/blood-2006-09-003004. PMID 17110453.
  13. ↑ Foster DC, Yoshitake S, Davie EW (1985). "The nucleotide sequence of the gene for human protein C." Proc Natl Acad Sci U S A. 82 (14): 4673–7. doi:10.1073/pnas.82.14.4673. PMC 390448. PMID 2991887.
  14. ↑ 14.0 14.1 Alhenc-Gelas M, Gandrille S, Aubry ML, Aiach M (2000). "Thirty-three novel mutations in the protein C gene. French INSERM network on molecular abnormalities responsible for protein C and protein S." Thromb Haemost. 83 (1): 86–92. PMID 10669160.
  15. ↑ Manco-Johnson MJ, Marlar RA, Jacobson LJ, Hays T, Warady BA (1988). "Severe protein C deficiency in newborn infants". J Pediatr. 113 (2): 359–63. doi:10.1016/s0022-3476(88)80284-1. PMID 3397801.
  16. ↑ 16.0 16.1 16.2 Reitsma PH, Bernardi F, Doig RG, Gandrille S, Greengard JS, Ireland H; et al. (1995). "Protein C deficiency: a database of mutations, 1995 update. On behalf of the Subcommittee on Plasma Coagulation Inhibitors of the Scientific and Standardization Committee of the ISTH". Thromb Haemost. 73 (5): 876–89. PMID 7482420.
  17. ↑ Broekmans AW, Bertina RM, Protein C: In: Recent Advances in Blood Coagulation. Volume 4. Edited by: Poller L. Churchill Livingstone New York; 1985:117.
  18. ↑ Greer IA (2003). "Inherited thrombophilia and venous thromboembolism". Best Pract Res Clin Obstet Gynaecol. 17 (3): 413–25. doi:10.1016/s1521-6934(03)00007-5. PMID 12787535.
  19. ↑ "Protein S Deficiency - StatPearls - NCBI Bookshelf".
  20. ↑ 20.0 20.1 20.2 Castoldi E, Hackeng TM (2008). "Regulation of coagulation by protein S." Curr Opin Hematol. 15 (5): 529–36. doi:10.1097/MOH.0b013e328309ec97. PMID 18695379.
  21. ↑ Dahlbäck B (2018). "Vitamin K-Dependent Protein S: Beyond the Protein C Pathway". Semin Thromb Hemost. 44 (2): 176–184. doi:10.1055/s-0037-1604092. PMID 28905350.
  22. ↑ Simmonds RE, Ireland H, Kunz G, Lane DA (1996). "Identification of 19 protein S gene mutations in patients with phenotypic protein S deficiency and thrombosis. Protein S Study Group". Blood. 88 (11): 4195–204. PMID 8943854.
  23. ↑ Gandrille S, Borgel D, Eschwege-Gufflet V, Aillaud M, Dreyfus M, Matheron C; et al. (1995). "Identification of 15 different candidate causal point mutations and three polymorphisms in 19 patients with protein S deficiency using a scanning method for the analysis of the protein S active gene". Blood. 85 (1): 130–8. PMID 7803790.
  24. ↑ Zöller B, Svensson PJ, He X, Dahlbäck B (1994). "Identification of the same factor V gene mutation in 47 out of 50 thrombosis-prone families with inherited resistance to activated protein C." J Clin Invest. 94 (6): 2521–4. doi:10.1172/JCI117623. PMC 330087. PMID 7989612.
  25. ↑ Rezende SM, Simmonds RE, Lane DA (2004). "Coagulation, inflammation, and apoptosis: different roles for protein S and the protein S-C4b binding protein complex". Blood. 103 (4): 1192–201. doi:10.1182/blood-2003-05-1551. PMID 12907438.
  26. ↑ van Vlijmen EF, Brouwer JL, Veeger NJ, Eskes TK, de Graeff PA, van der Meer J (2007). "Oral contraceptives and the absolute risk of venous thromboembolism in women with single or multiple thrombophilic defects: results from a retrospective family cohort study". Arch Intern Med. 167 (3): 282–9. doi:10.1001/archinte.167.3.282. PMID 17296885.
  27. ↑ 27.0 27.1 27.2 Mazza JJ (2004). "Hypercoagulability and venous thromboembolism: a review". WMJ. 103 (2): 41–9. PMID 15139558.
  28. ↑ "Factor V Leiden Deficiency - StatPearls - NCBI Bookshelf".
  29. ↑ 29.0 29.1 Poort SR, Rosendaal FR, Reitsma PH, Bertina RM (1996). "A common genetic variation in the 3'-untranslated region of the prothrombin gene is associated with elevated plasma prothrombin levels and an increase in venous thrombosis". Blood. 88 (10): 3698–703. PMID 8916933.
  30. ↑ Khan, Salwa; Dickerman, Joseph D (2006). Thrombosis Journal. 4 (1): 15. doi:10.1186/1477-9560-4-15. ISSN 1477-9560. Missing or empty |title= (help)
  31. ↑ Cunningham MT, Brandt JT, Laposata M, Olson JD (2002). "Laboratory diagnosis of dysfibrinogenemia". Arch Pathol Lab Med. 126 (4): 499–505. doi:10.1043/0003-9985(2002)126<0499:LDOD>2.0.CO;2. PMID 11900586.
  32. ↑ Thomas RH (2001). "Hypercoagulability syndromes". Arch Intern Med. 161 (20): 2433–9. doi:10.1001/archinte.161.20.2433. PMID 11700155.
  33. ↑ Caine GJ, Stonelake PS, Lip GY, Kehoe ST (2002). "The hypercoagulable state of malignancy: pathogenesis and current debate". Neoplasia. 4 (6): 465–73. doi:10.1038/sj.neo.7900263. PMC 1550339. PMID 12407439.
  34. ↑ Khorana AA (2003). "Malignancy, thrombosis and Trousseau: the case for an eponym". J Thromb Haemost. 1 (12): 2463–5. doi:10.1111/j.1538-7836.2003.00501.x. PMID 14675077.
  35. ↑ Rickles FR, Edwards RL (1983). "Activation of blood coagulation in cancer: Trousseau's syndrome revisited". Blood. 62 (1): 14–31. PMID 6407544.
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  37. ↑ Posthuma JJ, van der Meijden PE, Ten Cate H, Spronk HM (2015). "Short- and Long-term exercise induced alterations in haemostasis: a review of the literature". Blood Rev. 29 (3): 171–8. doi:10.1016/j.blre.2014.10.005. PMID 25467962.
  38. ↑ Arai M, Yorifuji H, Ikematsu S, Nagasawa H, Fujimaki M, Fukutake K; et al. (1990). "Influences of strenuous exercise (triathlon) on blood coagulation and fibrinolytic system". Thromb Res. 57 (3): 465–71. doi:10.1016/0049-3848(90)90262-b. PMID 2315896.
  39. ↑ Smith JE (2003). "Effects of strenuous exercise on haemostasis". Br J Sports Med. 37 (5): 433–5. doi:10.1136/bjsm.37.5.433. PMC 1751362. PMID 14514536.
  40. ↑ Röcker L, Drygas WK, Heyduck B (1986). "Blood platelet activation and increase in thrombin activity following a marathon race". Eur J Appl Physiol Occup Physiol. 55 (4): 374–80. doi:10.1007/BF00422736. PMID 3758037.
  41. ↑ K. A. Bremme, “Haemostatic changes in pregnancy,” Best Practice and Research, vol. 16, no. 2, pp. 153–168, 2003
  42. ↑ Antovic A, Blombäck M, Bremme K, He S (2002). "The assay of overall haemostasis potential used to monitor the low molecular mass (weight) heparin, dalteparin, treatment in pregnant women with previous thromboembolism". Blood Coagul Fibrinolysis. 13 (3): 181–6. doi:10.1097/00001721-200204000-00002. PMID 11943930.
  43. ↑ Cerneca F, Ricci G, Simeone R, Malisano M, Alberico S, Guaschino S (1997). "Coagulation and fibrinolysis changes in normal pregnancy. Increased levels of procoagulants and reduced levels of inhibitors during pregnancy induce a hypercoagulable state, combined with a reactive fibrinolysis". Eur J Obstet Gynecol Reprod Biol. 73 (1): 31–6. doi:10.1016/s0301-2115(97)02734-6. PMID 9175686.
  44. ↑ Goldhaber, Samuel Z.; Tapson, Victor F. (2004). "A prospective registry of 5,451 patients with ultrasound-confirmed deep vein thrombosis". The American Journal of Cardiology. 93 (2): 259–262. doi:10.1016/j.amjcard.2003.09.057. ISSN 0002-9149.
  45. ↑ Macklon, Nicholas S.; Greer, Ian A. (1997). "The deep venous system in the puerperium: an ultrasound study". BJOG: An International Journal of Obstetrics and Gynaecology. 104 (2): 198–200. doi:10.1111/j.1471-0528.1997.tb11044.x. ISSN 1470-0328.
  46. ↑ James, Andra H. (2009). "Venous Thromboembolism in Pregnancy". Arteriosclerosis, Thrombosis, and Vascular Biology. 29 (3): 326–331. doi:10.1161/ATVBAHA.109.184127. ISSN 1079-5642.
  47. ↑ James AH, Jamison MG, Brancazio LR, Myers ER (2006). "Venous thromboembolism during pregnancy and the postpartum period: incidence, risk factors, and mortality". Am J Obstet Gynecol. 194 (5): 1311–5. doi:10.1016/j.ajog.2005.11.008. PMID 16647915.
  48. ↑ Pabinger, Ingrid; Grafenhofer, Helga; Kyrle, Paul A.; Quehenberger, Peter; Mannhalter, Christine; Lechner, Klaus; Kaider, Alexandra (2002). "Temporary increase in the risk for recurrence during pregnancy in women with a history of venous thromboembolism". Blood. 100 (3): 1060–1062. doi:10.1182/blood-2002-01-0149. ISSN 1528-0020.
  49. ↑ Heit JA, Kobbervig CE, James AH, Petterson TM, Bailey KR, Melton LJ (2005). "Trends in the incidence of venous thromboembolism during pregnancy or postpartum: a 30-year population-based study". Ann Intern Med. 143 (10): 697–706. doi:10.7326/0003-4819-143-10-200511150-00006. PMID 16287790.
  50. ↑ Schreiber MA, Differding J, Thorborg P, Mayberry JC, Mullins RJ (2005). "Hypercoagulability is most prevalent early after injury and in female patients". J Trauma. 58 (3): 475–80, discussion 480-1. doi:10.1097/01.ta.0000153938.77777.26. PMID 15761339.
  51. ↑ Emmi G, Silvestri E, Squatrito D, Amedei A, Niccolai E, D'Elios MM; et al. (2015). "Thrombosis in vasculitis: from pathogenesis to treatment". Thromb J. 13: 15. doi:10.1186/s12959-015-0047-z. PMC 4399148. PMID 25883536.
  52. ↑ Kane MA, May JE, Frank MM (1973). "Interactions of the classical and alternate complement pathway with endotoxin lipopolysaccharide. Effect on platelets and blood coagulation". J Clin Invest. 52 (2): 370–6. doi:10.1172/JCI107193. PMC 302266. PMID 4683877.
  53. ↑ Nieto FJ, Sorlie P, Comstock GW, Wu K, Adam E, Melnick JL; et al. (1997). "Cytomegalovirus infection, lipoprotein(a), and hypercoagulability: an atherogenic link?". Arterioscler Thromb Vasc Biol. 17 (9): 1780–5. doi:10.1161/01.atv.17.9.1780. PMID 9327777.
  54. ↑ Tamaki H, Khasnis A (2015). "Venous thromboembolism in systemic autoimmune diseases: A narrative review with emphasis on primary systemic vasculitides". Vasc Med. 20 (4): 369–76. doi:10.1177/1358863X15573838. PMID 25750012.
  55. ↑ Kravitz MS, Shoenfeld Y (2005). "Thrombocytopenic conditions-autoimmunity and hypercoagulability: commonalities and differences in ITP, TTP, HIT, and APS". Am J Hematol. 80 (3): 232–42. doi:10.1002/ajh.20408. PMID 16247748.
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  57. ↑ Kristinsson SY (2010). "Thrombosis in multiple myeloma". Hematology Am Soc Hematol Educ Program. 2010: 437–44. doi:10.1182/asheducation-2010.1.437. PMID 21239832.
  58. ↑ Lip GY, Gibbs CR (1999). "Does heart failure confer a hypercoagulable state? Virchow's triad revisited". J Am Coll Cardiol. 33 (5): 1424–6. doi:10.1016/s0735-1097(99)00033-9. PMID 10193748.
  59. ↑ Breitenstein A, Glanzmann M, Falk V, Maisano F, Stämpfli SF, Holy EW; et al. (2015). "Increased prothrombotic profile in the left atrial appendage of atrial fibrillation patients". Int J Cardiol. 185: 250–5. doi:10.1016/j.ijcard.2015.03.092. PMID 25814212.

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