Selective serum IgA deficiency in Icelanders. Frequency, family studies and Ig levels.

More than 15,000 Icelanders (6.1% of the population), mostly healthy male blood donors, were screened in 1974-79 for selective IgA deficiency (SIgAD) by immunodiffusion (Ouchterlony). The frequency of SIgAD among blood donors was 1/633 (0.158%). Population and family screening yielded 35 individuals classified as IgA-deficient. Immunoglobulins A, G, M and E were measured in 119 family members of 18 propositi found by screening. Pedigree studies suggested both autosomal dominant and recessive modes of inheritance of SIgAD. A trend toward clustering of similar IgG and IgE levels (within the normal ranges) was apparent in several families. An increased IgG level in family members with SIgAD was significantly more frequent (p less than 0.001) than in members with normal levels of IgA. IgG levels were high in 12 (44%) and normal in 15 of 27 subjects with low or deficient IgA levels who were all healthy when examined, and only 5 gave a history of allergy or recurrent respiratory infections. It is suggested that immune response genes may cause the difference in Ig levels among the SIgAD family members.