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

Abstract

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 (Sµ); Sac I. Differences in genotype distributions between the study groups were only detected with the S probe which detects polymorphism of both Sµ and Sα1 (the switch region of IgA). Two alleles of Sα1 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.