severe combined immunodeficiency

severe combined immunodeficiency n a rare congenital disorder of the immune system that is characterized by inability to produce a normal complement of antibodies and T cells and that results usu. in early death abbr. SCID called also severe combined immune deficiency, severe combined immunodeficiency disease see ADENOSINE DEAMINASE

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(SCID) a group of rare congenital disorders characterized by gross impairment of both humoral and cell-mediated immunity and absence of T lymphocytes; some forms are also characterized by a lack of B lymphocytes. In most cases all classes of immunoglobulins are nearly or completely absent, and there is marked lymphocytopenia. Persistent diarrhea, chronic mucocutaneous candidiasis, and failure to thrive occur in infancy. Blood transfusions can result in graft-versus-host disease and routine vaccinations in fatal infection. Unless immune function is restored by a histocompatible bone marrow or fetal tissue transplant or the patient is kept in gnotobiotic isolation, death from opportunistic infection usually occurs before the first birthday. In approximately 50 per cent of cases, the disorder is X-linked and due to a defect in the γ chain of the receptor for IL-2 and other interleukins. B lymphocyte numbers are usually normal. The remaining 50 per cent of cases are of autosomal recessive inheritance and have varying etiologies, including defects in activity of adenosine deaminase, purine-nucleoside phosphorylase, or Janus kinase 3 (JAK3). A rare type of the autosomal recessive form is called reticular dysgenesis.