Histocompatibility antigens and insulin-dependent diabetes: a study of 20 Brazilian families.

1. The relationship between histocompatibility antigens (HLA) and insulin-dependent diabetes was examined. The relative frequency of HLA and the relative risk were determined for 20 families containing 82 individuals, 23 of whom had insulin-dependent diabetes. The control group contained 102 individuals. 2. The B8, B13, and B15 antigens had the highest relative frequency in the group of diabetic patients, whereas B5, B7 and B12 were lowest. A high relative frequency of histocompatibility antigens was found not only in the diabetic patients, but also in their parents and siblings. There was a predominance of A2B8, A2B15, and A9B15 haplotypes in the diabetic population. The diabetic siblings had identical haplotypes. 3. These data support previous reports suggesting genetic linkage between susceptibility to diabetes and the histocompatibility antigen system.