Racial differences in juvenile-type diabetes are consistent with more than one mode of inheritance

The ratio of the prevalences of insulin-dependent type (juvenile) diabetes (IDDM) in blacks and Caucasians is examined. It has been argued that this ratio is of the same order as the estimated proportion of Caucasian genes in the American black population. It has been further argued that this observation, together with an assumption of equal penetrances in the two races, is consistent with autosomal dominant inheritance for IDDM. The present paper shows that the ratio is equally compatible with a three-allele model which, moreover, incorporates observed immunogenetic heterogeneity within IDDM. This three-allele heterogeneity model exhibits some features of both dominant and recessive inheritance. The model predicts that, compared with Caucasians, there will be less pancreatic autoimmunity in the black IDDM population and lower recurrence risks to relatives of black diabetics. These predictions can be tested in future studies.