Polyclonal hyper-immunoglobulin G1(A1) syndrome. Evidence for a dominant immunoglobulin production regulator within the human immunoglobulin heavy chain gene complex.

The hyper-IgG1(A1) syndrome entails a polyclonal selective increase of the serum levels of immunoglobulin (Ig) G1 and to a lesser extent of IgA1; this is not mediated by malignancy, infectious or autoimmune diseases or environmental agents. In three generations of a family, all the affected individuals carried an immunoglobulin heavy chain (IgH) allele distinguished by restriction fragment length polymorphism analysis; the IgH allele was not present in non-affected family members. A 32:1 chance for the linkage of this rare IgH haplotype with the hyper-IgG1(A1) syndrome in the family argues for a dominant regulator located at the human IgH locus having a selective influence on the production of IgG1 and IgA1.