DQ beta restriction fragment length polymorphism and its relationship to insulin dependent diabetes mellitus.

HLA Class II serological and DQ beta restriction fragment length polymorphisms (RFLPs) were compared in 69 patients with insulin-dependent diabetes mellitus (IDDM) and 81 healthy British Caucasoid controls. The backbone of the analysis was formed by two Taq 1 RFLPs of the DQ beta region designated T2 omega and T6. The two are not allelic and can be inherited individually, together on one, or separately on both, parental haplotypes, the latter almost invariably in association with DR4. In our study the frequency in IDDM patients of both T2 omega and T6 together (relative risk for IDDM = 6.4) is similar to that of DR3/DR4 (relative risk for IDDM = 5.4) with an even higher relative risk for IDDM when they are combined, (relative risk = 18 with 95 per cent confidence limits between 14 and 22). We have thus defined DQ beta RFLPs which tightly associate with IDDM individuals with DR4.