Glucose-6-phosphate dehydrogenase deficiency: Difference between revisions

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==Diagnosis==
==Diagnosis==
===Laboratory diagnosis==
===Laboratory diagnosis===
The diagnosis is generally suspected when patients from certain ethnic groups develop [[anemia]], [[jaundice]] and symptoms of [[hemolysis]] after challenge to any of the above causes, especially when there is a positive family history.
The diagnosis is generally suspected when patients from certain ethnic groups develop [[anemia]], [[jaundice]] and symptoms of [[hemolysis]] after challenge to any of the above causes, especially when there is a positive family history.


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* When there are sufficient grounds to suspect [[G6PD]], a direct test for [[G6PD]] is the "Beutler fluorescent spot test", which has largely replaced an older test (the Motulsky dye-decolouration test).
* When there are sufficient grounds to suspect [[G6PD]], a direct test for [[G6PD]] is the "Beutler fluorescent spot test", which has largely replaced an older test (the Motulsky dye-decolouration test).
* Other possibilities are direct DNA testing and/or sequencing of the G6PD gene.
* Other possibilities are direct DNA testing and/or sequencing of the G6PD gene.
 
====Beutler fluorescent spot test: Late diagosis====
The ''Beutler fluorescent spot test'' is a rapid and inexpensive test that visually identifies [[Nicotinamide adenine dinucleotide phosphate|NADPH]] produced by [[G6PD]] under [[ultraviolet light]]. When the blood spot does not fluoresce, the test is positive; it can be false-positive in patients who are actively hemolysing. It can therefore only be done several weeks after a hemolytic episode.
The '''Beutler fluorescent spot test''' is a rapid and inexpensive test that visually identifies [[Nicotinamide adenine dinucleotide phosphate|NADPH]] produced by [[G6PD]] under [[ultraviolet light]]. When the blood spot does not fluoresce, the test is positive; it can be false-positive in patients who are actively hemolysing. It can therefore only be done several weeks after a hemolytic episode.
 
====Early diagnosis: Heinz bodies====
When a macrophage in the spleen "sees" an [[RBC]] with a [[Heinz body]], it removes the precipitate and a small piece of the membrane, leading to characteristic "bite cells". However, if a large number of [[Heinz bodies]] are produced, as in the case of [[G6PD deficiency]], some [[Heinz bodies]] will nonetheless be visible when viewing [[RBC]]s that have been stained with crystal violet. This easy and inexpensive test can lead to an initial presumption of [[G6PD deficiency]], which can be confirmed with the other tests.
When a macrophage in the spleen "sees" an [[RBC]] with a [[Heinz body]], it removes the precipitate and a small piece of the membrane, leading to characteristic "bite cells". However, if a large number of [[Heinz bodies]] are produced, as in the case of [[G6PD deficiency]], some [[Heinz bodies]] will nonetheless be visible when viewing [[RBC]]s that have been stained with crystal violet. This easy and inexpensive test can lead to an initial presumption of [[G6PD deficiency]], which can be confirmed with the other tests.



Revision as of 00:23, 19 September 2012

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive hereditary disease featuring abnormally low levels of the G6PD enzyme, which plays an important role in red blood cell function. Individuals with the disease may exhibit non-immune hemolytic anemia in response to a number of causes. It is closely linked to favism, a disorder characterized by a hemolytic reaction to consumption of broad beans, with a name derived from the Italian name of the broad bean (fava). Sometimes the name, favism, is alternatively used to refer to the enzyme deficiency as a whole.

Epidemiology and Demographics

  • G6PDD is said to be the most common enzyme deficiency disease in the world, affecting approximately 400,000,000 people globally.[1]
  • A side effect of this disease is that it confers protection against malaria, in particular the form of malaria caused by Plasmodium falciparum, the most deadly form of malaria.
  • A similar relationship exists between malaria and sickle-cell disease. An explanation is that cells infected with the Plasmodium parasite are cleared more rapidly by the spleen. This phenomenon might give G6PD deficiency carriers an evolutionary advantage.

Classification

There are four forms of G6PD:

  1. Hereditary nonspherocytic hemolytic anemia
  2. Severe deficiency
  3. Mild deficiency
  4. Non-deficient variant
  5. Favism is a disorder characterized by hemolytic anemia in response to ingestion of fava beans. Favism as a diagnosis has been known since antiquity, perhaps in relation to Pythagoras, among others. All individuals with favism show G6PD deficiency. However, not all individuals with G6PD deficiency show favism. For example, in a small study of 757 Saudi men, more than 42% showed G6PD deficiency, but none reported symptoms of favism, despite fava in the diet.[2] Favism is known to be more prevalent in infants and children, and G6PD genetic variant can influence chemical sensitivity. Other than this, the detailed chemical relationship between favism and G6PD is not well known.

Pathophysiology

Mechanism of G6PD
Mechanism of G6PD















History and Symptoms

History

Symptoms

Diagnosis

Laboratory diagnosis

The diagnosis is generally suspected when patients from certain ethnic groups develop anemia, jaundice and symptoms of hemolysis after challenge to any of the above causes, especially when there is a positive family history.

Generally, tests will include:

Beutler fluorescent spot test: Late diagosis

The Beutler fluorescent spot test is a rapid and inexpensive test that visually identifies NADPH produced by G6PD under ultraviolet light. When the blood spot does not fluoresce, the test is positive; it can be false-positive in patients who are actively hemolysing. It can therefore only be done several weeks after a hemolytic episode.

Early diagnosis: Heinz bodies

When a macrophage in the spleen "sees" an RBC with a Heinz body, it removes the precipitate and a small piece of the membrane, leading to characteristic "bite cells". However, if a large number of Heinz bodies are produced, as in the case of G6PD deficiency, some Heinz bodies will nonetheless be visible when viewing RBCs that have been stained with crystal violet. This easy and inexpensive test can lead to an initial presumption of G6PD deficiency, which can be confirmed with the other tests.

Treatment

The most important measure is prevention - avoidance of the drugs and foods that cause hemolysis. Vaccination against some common pathogens (e.g. hepatitis A) may prevent infection-induced attacks.

In the acute phase of hemolysis, blood transfusions might be necessary, or even dialysis in acute renal failure. Blood transfusion is an important symptomatic measure, as the transfused red cells are generally not G6PD deficient.

Some patients benefit from removal of the spleen (splenectomy), as this is an important site of red blood cell destruction. Folic acid should be used in any disorder featuring a high red blood cell turnover. Although vitamin E and selenium have antioxidant properties, their use does not decrease the severity of G6PD deficiency.

References

  1. http://www.rddiagnostics.com/g6pd_faq.htm
  2. "Common G6PD variant from Saudi population". Retrieved 2007-10-28.
  3. Gaskin RS, Estwick D, Peddi R (2001). "G6PD deficiency: its role in the high prevalence of hypertension and diabetes mellitus". Ethnicity & disease. 11 (4): 749–54. PMID 11763298.
  4. "The G6PD Deficiency Homepage -- Table 2". Retrieved 2007-10-28.
  5. Raupp P, Hassan JA, Varughese M, Kristiansson B (2001). "Henna causes life threatening haemolysis in glucose-6-phosphate dehydrogenase deficiency". Arch. Dis. Child. 85 (5): 411–2. PMID 11668106.

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