Insulin dependent diabetes: a comparison of families with single and multiple affected siblings.

Families (n = 14) with more than 1 sibling with insulin dependent diabetes were matched with families of similar size and age distribution containing only 1 affected child. The distribution of HLA haplotypes, age of onset of disease, and seasonal onset of disease were compared in the two groups. The data are not consistent with the hypothesis of a single autosomal recessive gene linked to the HLA region. The data do not permit a choice between other current hypotheses although they are compatible with the theory of 2 genes linked to the HLA region, acting additively, and requiring interaction either with environmental factors or other disease susceptibility genes. Diabetic children in the multiplex and simplex families did not differ in the month of onset of symptoms nor in the age at diagnosis although three multiplex pedigrees in which diabetes developed in all affected children before the age of 6 years were identified.