HLA antigens and Graves' disease in Black South Africans

This study concerns the frequencies with which 36 HLA-A, -B and -C antigens occurred in 84 Black Africans with Graves' disease and in 311 Black controls. In the hyperthyroid patients significant reductions were found in the frequencies of HLA-B7 ( P <0.001, relative risk (RR) 0.33), HLA-Bw42 ( P <0.001, RR 0.32) and the HLA-B7-Bw42 crossreactive group (CREG) ( P <0.0001, RR 0.27), and in the frequencies of the phenotypic combinations HLA-A1, B7 ( P <0.001) and Aw30, B7-Bw42 ( P <0.001). HLA-B8 was increased in frequency ( P <0.01, RR 2.84). In patients without circulating antithyroglobulin or antimitichondrial antibodies the frequencies of HLA-A2 and B17 were increased when compared to those with antibodies or to the controls. In patients with and without clinically evident infiltrative ophthalmopathy the frequencies of HLA antigens were similar. In 62 Caucasian patients with Graves' disease, no antigens or phenotypic combinations occurred with increased or decreased frequency when compared to 278 controls.
Analysis of the frequencies of 9 HLA antigens and phenotypic combinations common in Caucasians but rare in Blacks revealed that only two antigens (A2 and B8) occurred with increased frequency in Black patients, suggesting that a contribution of Caucasian genes to the Black thyrotoxic subjects was unlikely.
Similarly, only one common Black antigen (A28) of 8 common antigens and phenotypic combinations, occurred in Caucasian patients with a frequency similar to that of Black controls. Thus it is unlikely that Black genes contributed to the lack of a significant increase of HLA antigens in the Caucasian thyrotoxic patients. The possession of HLA-B7-Bw42 CREG or related genes may be a protection against Graves' disease in Black Africans.