Immunoglobulin allotype Gm(1,2;21) in ankylosing spondylitis with peripheral arthritis.

Frequencies of immunoglobulin G (Gm) allotypes were determined in 240 patients with ankylosing spondylitis (AS). The uncommon phenotype Gm(1,2;21) was increased in frequency in 55 patients with AS and peripheral arthritis (14.5% v 3.5% of healthy blood donors; p less than 0.05). In 16 patients with arthritis only of wrist/hand or ankle/forefoot, or both, the Gm(1,2;21) frequency was even higher (31.3%; p less than 0.0005). Patients with AS negative for the HLA antigen B27 (n = 28) differed from the B27 positive patients (n = 205) with regard to the frequency of the Gm(1,2,3;5,21) phenotype (39.3% v 9.3%; p less than 0.0005). These findings support the notion of genetic heterogeneity among patients with AS.