]> 2026-07-31T09:42:06+00:00 WBR0321 0 en Delayed separation of umbilical cord Leukocyte adhesion deficiency (type I) is due to a defect in LFA-1 integrin. Patients typically present with recurrent bacterial infections with no pus formation and delayed separation of the umbilical cord. Absence of germinal centers on lymph node biopsy Absence of germinal centers on lymph node biopsy due to absence of B cells is found in SCID. Thrombocytopenic purpura and eczema Thrombocytopenic purpura, eczema, and infections are found in patients with Wiskott-Aldrich syndrome, caused by inability of T-cell reorganization of actin cytoskeleton. Self-mutilation and choreoathetosis Self-mutilation and choreoathetosis are found in patients with Lesch-Nyhan syndrome, caused by a deficiency of HGPRT. Precipitation of monosodium urate crystals in joints on arthrocentesis Gout is caused by precipitation of monosodium urate crystals (MSU) in joints. It is a common complication of hyperuricemia. Adenosine deaminase deficiency, the likely culprit in this patient, is an important cause of severe combined immunodeficiency (SCID). SCID is a syndrome encompassing a group of rare congenital disorders characterized by B cell and T cell deficiency. All forms of SCID are inherited, most common of which is X-linked. X-linked SCID is caused by a deficiency of IL-2 receptor gamma leading to a failure in the development and differentiation of T and B cells. Adenosine deaminase deficiency is the second most common cause of SCID. Adenosine deaminase is coded for by a gene on chromosome 20 and is essential for the breakdown of purines. Loss of this enzyme leads to the accumulation of dATP causing feedback inhibit the activity of ribonucleotide reductase. As ribonucleotide reductase is essential for dNTP synthesis, DNA replication would cease and lymphocyte proliferation is subsequently inhibited. Accordingly, patients with SCID present early in childhood with failure to thrive and recurrent infections by viruses, bacteria and fungi. Work-up may reveal thymic aplasia and loss of germinal centers on lymph node biopsy. Currently, the only curative treatment for SCID is bone marrow transplantation despite several controversial attempts at introducing gene therapy as an alternative (mainly due to the high incidence of leukemias).<br/> '''Educational Objective:''' Adenosine deaminase deficiency is a common cause of severe combined immunodeficiency (SCID).<br/> '''References:''' Weinberg K, Parkman R. Severe combined immunodeficiency due to a specific defect in the production of interleukin-2. N Engl J Med. 1990;322(24):1718-23.<br> Parkman R, Gelfand EW, Rosen FS, Sanderson A, Hirschhorn R. Severe combined immunodeficiency and adenosine deaminase deficiency. N Engl J Med. 1975;292(14):714-9.<br> First Aid 2014 page 68. Biochemistry B General Principles 2020-10-28T00:10:57Z 2459150.5076042 WBR0321