C4 null genes in American whites and blacks with myositis

The frequencies of C4A and C4B alleles were determined in 66 adults with myositis in relation to HLA class I and II. In whites with myositis, the C4A*Q0 allele occurred in 13/31 (47%) as compared to 25/101 (25%) normal controls (p=0.08, relative risk=2.7). Only 11/35 (31%) of black patients with myositis had a C4A*Q0 allele compared to 11/55 (20%) of controls (p=NS, RR=1.8)