Diabetes mellitus: discrimination between single locus and multifactorial models of inheritance.

Family data from 6,559 diabetic propositi were analyzed using the method of complex segregation analysis in an attempt to discriminate the two models of two-allele single-locus inheritance and multifactorial inheritance for early, middle, and late onset diabetes. The three parameters in the single locus model were: degree of dominance, penetrance, and proportion of phenocopies. In early onset diabetes, the heritability estimated from the multifactorial model was so high as to inidcate major gene action. In middle and late onset diabetes, best fitting single-locus models were found to explain the data as well as the multifactorial model.