Severe combined immunodeficiency diseases

Metabolic defects in severe combined immunodeficiency in man and animals

Severe combined immunodeficiency (SCID) was originally thought to be one disease. Accumulating evidence indicates that SCID is a heterogeneous group of diseases that are clinically similar but are caused by quite different biochemical abnormalities. The best-studied form of SCID is that associated with an autosomal recessive inheritance pattern of adenosine deaminase (ADA) deficiency. Several biochemical mechanisms have been postulated to explain how a deficiency of ADA causes immune dysfunction. In forms of SCID not associated with ADA deficiency, other biochemical abnormalities have been detected. These abnormalities include deficiency in biotin-dependent carboxylases, alteration in lymphocyte surface membranes and irregularities in cytokine production. Two animal models for SCID now exist. Neither of these models is associated with ADA deficiency. Evidence for a possible defect in purine metabolism in one model has been demonstrated.

Metabolic investigations of fibroblasts from horses, Equus caballus, with hereditary severe combined immunodeficiency

In an attempt to determine the metabolic defect causing severe combined immunodeficiency (SCID) in horses in which altered purine metabolism has been observed, various parameters of purine and pyrimidine metabolism were evaluated. The activities of nine purine enzymes (adenosine kinase, purine nucleoside phosphorylase, deoxyadenosine kinase, deoxycytidine kinase, 5'-nucleotidase, AMP deaminase, hypoxanthine-guanine phosphoribosyl transferase, and adenine phosphoribosyl transferase were measured in fibroblasts. All activities determined for SCID horses were normal. Uptake of 10 microM adenosine or 2'-deoxyadenosine (a growth inhibitory concentration for SCID fibroblasts) by SCID fibroblasts was identical to that found for normal fibroblasts in the presence of both 1 and 50 microM phosphate. The Km determined for the transport of both adenosine and 2'-deoxyadenosine was 35 microM. In the presence of p-nitrobenzylthioguanosine (a nucleoside transport inhibitor), 2'-deoxyadenosine uptake was inhibited to the same extent in all fibroblast lines tested. To determine if the last step in pyrimidine biosynthesis might be altered in SCID fibroblasts, UMP synthase activities were evaluated but found to be normal (0.5 nmol UMP formed/min/mg protein).

Acquired immunodeficiency syndrome with severe gastrointestinal manifestations in Haiti

29 patients (19 males and 10 females) in Haiti were diagnosed as having acquired immunodeficiency syndrome. Their clinical presentation was characterised by unexplained chronic diarrhoea, prolonged fever, extreme weight loss, anorexia, and severe infections. The infectious agents included: Candida albicans (27 patients), Mycobacterium tuberculosis (7 patients), Cryptosporidium (11 patients), Pneumocystis carinii (2 patients), cytomegalovirus (4 patients), and herpes virus (3 patients). In 1 woman Kaposi's sarcoma developed during the course of her disease. Immunological studies of 20 patients revealed profound cell-mediated immune deficiency with cutaneous anergy, marked decrease in the number of T helper cells, and impairment of lymphocyte proliferation. 18 patients died.

Immunodeficiency and syndromes: a nosographic approach

Immunodeficiency disorders can be classified on clinical grounds into two broad groups according to whether all features are the result of the immune defect (immunodeficiency syndromes) or whether many, even prominent, features cannot be explained by the immune defect (syndromes with immunodeficiency). X-linked agammaglobulinemia and X-linked chronic granulomatous disease are paradigmatic examples of immunodeficiency syndromes. Despite some overlap (for instance extra-immune symptoms, although minor, are present in several variants of severe combined immunodeficiency and chronic granulomatous disease) immunodeficiency syndromes and syndromes with immunodeficiency are easily distinguishable. Together with the pathogenetic classification of the WHO, the present approach to a clinical classification amplifies the operational concept of immunodeficiency also from a therapeutic point of view.