Immunoglobulin metabolism in ataxia telangiectasia.

Immunoglobulin metabolism has been studied in five patients with ataxia telangiectasia and in control subjects. Serum IgG levels were normal, increased, or decreased, reflecting normal, increased, or decreased synthetic rates, respectively. Serum IgM concentration was normal in three cases and slightly elevated in two cases. IgM turnover studies in the three cases with normal serum IgM levels showed normal IgM synthetic and catabolic rates. None of the five patients with ataxia telangiectasia had detectable serum IgA, and the maximum IgA synthetic rates possible for these patients were 0.3-10% of the normal mean synthetic rate (24 +/- 15 mg/kg per day) of 12 control individuals. Three of the patients had normal IgA fractional catabolic rates: 22% of the intravascular pool per day vs. 25 +/- 4% in controls. In two patients, fractional catabolic rates 4 and 20 times normal were found. In these cases, metabolic turnover, in vitro precipitation, radioimmunoelectrophoresis, and (or) the C'la fixation and transfer test provided evidence for the presence of a circulating antibody directed against IgA causing immune elimination of the molecule. These studies suggest that therapy with exogenous IgA may not be possible in some patients with ataxia telangiectasia or in other subjects with dysgammaglobulinemia.