Heredity and diabetes

Summary

Although diabetes mellitus shows a marked familial tendency, the exact mode of inheritance of the disease, as yet, has not been determined completely, chiefly because of the absence of full concordance between the diabetic genotype and phenotype. The percentage of cases with positive family histories of diabetes varies inversely with the age at onset of the disease. The age at onset is earlier in those cases with positive family histories of diabetes than in those without such family histories and is especially early in those with bilateral family histories. On the whole, the available evidence favors the hypothesis that diabetes is inherited as a recessive. The age at onset of the disease is positively correlated in sibs but not, or only slightly, correlated in parent-offspring pairs. There is conflicting evidence as to whether diabetes is more likely to appear in the like-sexed than in the unlike-sexed sibs of diabetic propositi, but the present observations suggest that if any such relationship exists, it can be explained on the basis of the preponderance of female diabetics.