A difference between the inheritance of classical juvenile-onset and maturity-onset type diabetes of young people.

A difference in the inheritance of diabetes has been shown between the families of twenty-six patients with maturity-onset type diabetes of young people (MODY) and families of thirty-five patients with classical juvenile-onset diabetes (JOD). In the families of MODY: 1) twenty-two of twenty-six (85 per cent) propositi had a diabetic parent; 2) 46 per cent of families showed direct vertical transmission of diabetes through three generations; 3) of forty-seven tested siblings twenty-five (53 per cent) had latent diabetes; 4) the diabetic phenotype in the families was consistent, most affected individuals having a noninsulin requiring type of disease. These findings are compatible with autosomal dominant inheritance of MODY, although they do not exclude multifactorial inheritance. In contrast, in the families of JOD: 1) only four (11 per cent) of propositi had a diabetic parent; 2) three generation inheritance was found in only two (6 per cent) of JOD families, and 3) of seventy-four tested siblings eight (11 per cent) were diabetic. This difference provides further evidence of genetic heterogeneity in diabetes mellitus and indicates that there is a need for careful definition of the phenotype of diabetes in populations in which the genetics of diabetes is to be analyzed. Diabetes 24:44-53, January, 1975.