Correlation between deficiency of immunoglobulin subclass G3 and Gm allotype.

Gm allotypes were investigated in 63 Swedes: 46 females and 17 males, in whom serum IgG3 was below 0.35 g/l. Both monoclonal antibodies and polyclonal antisera were used for the quantification. Concentrations of the other IgG subclasses were within the age-related normal ranges. The distribution of the IgG1 genetic markers G1m(a,x,f) differed markedly from that observed in normal Swedes (p less than 0.001). Thus G1m(a) was present in 60 subjects as compared to an expected 36, and phenotype G1m(-f) in 34 subjects as against an expected 8. The mean IgG3 concentration was numerically lower in the G1m(-f) group than in the G1m(+f) cohort, and individuals with IgG3 levels 0.10 g/l were more frequent in the G1m(-f) group. Among Caucasians, G3mg is in linkage disequilibrium with G1ma and our interpretations is that the haplotype G1ma;ax G2m-n G3mg is markedly increased in individuals with IgG3 deficiency.