22. IgA deficiency—hereditary aspects

Familial cases of selective immunoglobulin A deficiency have been documented, but the mode of inheritance remains unsettled. The propositus of the present study, a 9-year-old girl with a past history of frequent upper respiratory tract infections, had an unusually low serum IgA level, between 0.5 and 2.0 mg/100 ml (i.e., IgA detectable by double diffusion but not by the radial immunodiffusion technique). The mother of the patient showed a total lack of serum IgA and suffered from chronic urinary tract infection. The father and brother of the propositus and the maternal relatives tested had normal IgA levels. Bothe patients had normal karyotypes. In the propositus. IgA was detected in saliva and intestinal juice, but IgM was present in higher concentrations in these secretions. Direct immunofluorescent studies of both rectal and small intestinal mucosa revealed IgA-containing cells, but IgM-containing cells were predominant. In the mother, no IgA was detectable in whole saliva concentrated 20 times, and the rectal mucosa was completely devoid of IgA-containing cells, whereas IgM-containing cells were abundant. These findings suggest that IgA deficiency may differ in degree of severity. The daughter in this family could be heterozygous for a recessive trait, while the mother is homozygous. On the other hand, an autosomal dominant mode of transmission with variable gene expressivity cannot be ruled out.