IgA2 allotypes determined by restriction fragment length polymorphism in IgA deficiency. Re-expression of the silent A2m(2) allotype in the children of IgA-deficient patients.

IgA2 allotyping was performed on DNA from 60 IgA-deficient Caucasian individuals. The frequency of A2m(2) was not statistically different from that of normal controls. Two informative families were selected for further studies. In both families, the A2m(2) allotype (derived from the IgA-deficient parent) was inherited by some of the children, as determined by Southern blotting experiments. In all cases the 'silent' IgA2m2 gene was re-expressed, as judged by conventional serological allotyping of serum proteins. These data strongly argue against structural gene deletions or mutations as a cause of IgA deficiency.