HLA associations with rheumatoid arthritis in African blacks.

The HLA-A, B, C and DR antigens were determined in a group of 100 blacks with classical or definite rheumatoid arthritis (RA) in Durban, South Africa. Fifty-six of these patients were also tested for the DQ antigens. There was a significant association of HLA-DR4 with RA (chi 2 = 77.2; p less than 0.0001). The frequency of DR4 in RA was 44% in comparison with 10% in controls (relative risk 7.4). An unusual finding was a significant increase in the frequency of HLA-B8 in 35% of patients with RA compared to 12.5% of controls (p less than 0.001; relative risk 3.8). There was no linkage disequilibrium between DR4 and B8 to explain the latter association.