We describe two brothers with ataxia telangiectasia (AT) of which one was unique in that he had no detectable IgG and IgA concentrations in the serum or saliva. The other brother had the more common IgA deficiency in the serum and saliva. Neither patient had a history of undue sinopulmonary infections. In spite of the absence of these immunoglobulins in the sera, there were cells in the bone marrow and peripheral blood that stained with fluorescein-labeled anti-IgG and anit-IgA. Both patients had demonstrable humoral antibody and cell-mediated immune responses to the antigens tested. We also discuss possible pathophysiological mechanisms causing the above defects.

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