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.