Linkage and association of insulin gene VNTR regulatory polymorphism with polycystic ovary syndrome

Background Polycystic ovary syndrome (PCOS) is a common endocrine disorder affecting up to 10% of women of reproductive age. Women with anovulatory PCOS have hyperinsulinaemia, insulin resistance, and dyslipidaemia, and the syndrome is associated with greatly increased risks of non-insulin-dependent diabetes mellitus and cardiovascular disease and it often clusters in families. The VNTR (variable number of tandem repeats) locus upstream of the insulin gene (INS) regulates insulin expression. We have studied INS VNTR as a candidate genetic locus for susceptibility to PCOS. Methods We evaluated linkage of PCOS to the INS VNTR locus on chromosome 11p15·5 in 17 families with several cases, and looked for an association between VNTR and PCOS in two additional clinic populations. VNTR genotypes were designated I/I, I/III, and III/III and linkage disequilibrium mapping was used to test the primary role of the VNTR. Findings In a group of PCOS/male pattern baldness families, we obtained positive evidence for linkage to 11p15·5 (p=0·002). The INS VNTR III/III genotype was associated with an increased risk of PCOS in two independent case-control studies (odds ratios 8·20 [p=0·005] and 5·70 [p=0·043]). Multilocus linkage disequilibrium mapping suggests that VNTR itself is the predisposing locus. Interpretation Mapping of susceptibility to PCOS to the INS VNTR implies that PCOS is due, in part, to an inherited alteration in insulin production. The data suggest a mechanistic link between type 2 diabetes and PCOS, which is a risk factor for diabetes later in life.