Familial hyperproinsulinemia. An autosomal dominant defect.

We describe a genetic defect in a kindred in whom proinsulin or a proinsulin-like material constitutes the major fraction of circulating insulin immunoreactivity in both the fasting and stimulated states. The defect, familial hyperproinsulinemia, affects eight males and 10 females in four generations of the kindred, with an autosomal dominant mode of transmission. Familial hyperproinsulinemia is asymptomatic in the affected progeny, with no apparent relation to hypoglycemia or to the development of diabetes mellitus. This genetic defect may represent either a deficiency in the proinsulin cleaving enzyme (or enzymes) within the beta cell, or more probably, an abnormal species of proinsulin.