A number of immunodeficiency states are characterized by significantly lowered amounts of specific immunoglobulin isotypes. Of these, IgA deficiency is by far the most common. There are family-association data showing that IgA deficiency prevails in the same families as CVI, suggesting a relationship between these conditions. The spectrum of clinical symptoms of IgA deficiency is broad; many of those affected are asymptomatic, while others suffer from an assortment of serious problems. Recurrent respiratory and genitourinary tract infections resulting from lack of secreted IgA on mu-cosal surfaces are common. In addition, problems such as intestinal malabsorption, allergic disease, and autoimmune disorders may also be associated with low IgA levels. The reasons for this variability in the clinical profile of IgA deficiency are not clear but may relate to the ability of some, but not all, patients to substitute IgM for IgA as a mucosal antibody. The defect in IgA deficiency is related to the inability of IgA B cells to undergo normal differentiation to the plasma-cell stage. IgG2 and IgG4 may also be deficient in IgA-deficient patients. No causative defect in IgA genes has been identified, and the surface IgA molecules on these patients' B cells appear to be expressed normally. A gene outside of the im-munoglobulin gene complex is suspected to be responsible for this fairly common syndrome.
Other immunoglobulin deficiencies have been reported, but these are rarer. An IgM deficiency has been identified as an autosomal recessive trait. Victims of this condition are subject to severe infection by agents such as meningococcus, which causes fatal disease. IgM deficiency may be accompanied by various malignancies or by autoimmune disease. IgG deficiencies are also rare. These are often not noticed until adulthood and can be effectively treated by administration of immunoglobulin.
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