A genetic study of retinopathy in south Indian type 2 (non-insulin-dependent) diabetic patients.

Genetic marker studies in diabetic retinopathy are controversial and frequently complicated by possible independent associations of Type 1 (insulin-dependent) diabetes mellitus with the markers so far analysed. We have looked for associations of candidate genes with retinopathy in South Indian Type 2 (non-insulin-dependent) diabetic patients; patients were subdivided into those with exudative maculopathy (n = 53), proliferative retinopathy (n = 40) and patients free from diabetic retinopathy with a minimum disease duration of 15 years (n = 45). DNA was extracted from blood samples and studied by Southern blot hybridisation techniques and the following probe enzyme combinations: HLA-DQB1; Taq 1, HLA-DQA1; Taq 1, HLA-DRA; Bgl II, insulin gene hypervariable region; Pvu II and the switch region of the immunoglobulin IgM heavy chain gene (S mu); Sac I. Differences in genotype distributions between the study groups were only detected with the S mu probe which detects polymorphism of both S mu and S alpha 1 (the switch region of IgA). Two alleles of S alpha 1 were detected sized 7.4 kilobase and 6.9 kilobase. The frequency of 6.9 kilobase homozygotes was lower in proliferative retinopathy (19%) compared to patients free from diabetic retinopathy (54%, p = 0.005) and exudative maculopathy (46%, p = 0.03). This data suggests that there is a genetic predisposition to proliferative retinopathy in Type 2 (non-insulin-dependent) diabetes of South Indian origin and that this is determined by polymorphism of the heavy chain immunoglobulin genes located on chromosome 14.