Family studies in individuals with selective absence of gamma-A-globulin.

The immunoglobulins were studied in twenty-one individuals with isolated lack of γA-globulin and in eleven of their families. The propositi were normal blood donors and patients with ataxia telangiectasia, with rheumatoid arthritis, or in a few cases other conditions. With the exception of one family where the mother and one child lacked γA, no family members other than the propositi were affected. In the family members, the levels of γA-globulin and of other immunoglobulins were mostly within normal ranges. Furthermore, there was no association between the lack of γA-globulin and the Gm marker system. Anti-γA antibodies were found in seven propositi. The findings demonstrated that the lack of γA-globulin was usually not due to structural gene defects, but indicated some regulatory mechanism, with depression of γA synthesis.