BackgroundThe presence of the deletion allele of the angiotensin-converting enzyme (ACE) I/D polymorphism is associated with an excess risk of vascular disease and diabetic nephropathy.ObjectiveTo examine the importance of this polymorphism as a determinant of hypertension and impaired glucose metabolism in a population-based study of three ethnic groups and assess the potential modifying effect of gender.DesignPopulation-based cross-sectional study in South London. The population-based sample of 1577 men and women, age 40–59 years, was obtained from stratified random sampling of general practice lists where 25% of the residents were born outside the UK. The ACE I/D polymorphism was determined for 1366 individuals (86.6%): 462 whites, 462 of African descent and 442 of South Asian origin.ResultsThe genotype frequency within each ethnic group was in Hardy–Weinberg equilibrium. The frequencies were similar in whites and those of African descent (II, ID, DD: 18.4%, 49.6%, 32.0% for whites and 18.4%, 50.5%, 30.9% for those of African descent), but there was a much higher frequency of the II genotype in those of South Asian origin (39.8%, 41.8%, 18.3%; χ2= 77.6;P< 0.0001). There was no association between the I/D polymorphism and impaired glucose metabolism in any ethnic group. There were also no significant associations between the I/D polymorphism and hypertension in whites and in those of South Asian origin. This contrasts with a highly significant association between the D allele and hypertension in women of African descent (OR = 2.54; 95% CI 1.38–4.65;P= 0.003) but not in men of African descent (0.79; 0.36–1.72) (test for differences between sexesP= 0.023).ConclusionsThese observations provide estimates of the frequency distribution of the ACE I/D polymorphism in whites, in people of African descent and in people of South Asian origin. Moreover, these results highlight the potential importance of gender-dependent interactions between genetic background and expression of hypertensive phenotype.