Hyper-IgM syndrome is a type of hypogammaglobulinemia, characterized by normal or increased serum IgM levels and depressed IgG and IgA levels. This is associated with a block in B-cell class switching from IgM to IgG. The syndrome has been described in male patients with a mutation in the CD40L gene located on the X chromosome. The syndrome may be inherited in X-linked or autosomal recessive pattern. Some patients may not have abnormal IgM levels, and identification of the abnormal CD40L leads to the diagnosis. Hyper-IgM syndrome is associated with lymphadenopathy, recurrent infections, neutropenia, autoimmune syndromes, and a susceptibility to infections. Patients are especially more likely to develop Pneumocystis carinii, histoplasmosis, toxoplasmosis, candida, cytomegalovirus, and mycobacterial infections. The syndrome is considered in the differential diagnosis of Pneumocystis carinii, pneumonia and cryptosporidium related gastrointestinal disease. Infections typically...
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