Serum insulin and growth hormone response patterns in monozygotic twin siblings of patients with juvenile-onset diabetes.

To detect abnormalities in the secretion of insulin and growth hormone in monozygotic twin siblings of patients with juvenile-onset diabetes, their responses during oral, cortisone-primed oral, and intravenous, glucose tolerance tests and intravenous tolbutamide tests were compared to those of matched controls. The twins had higher mean serum insulin levels during all tests, but differences reached statistical significance (P less than 0.02) only in the cortisone-primed test. Growth hormone levels were higher in the twins (P less than 0.04) in the intravenous tolbutamide tolerance test. The frequency of abnormal oral glucose tolerance tests among controls, diabetic monozygotic twins and the offspring of two diabetic parents was also compared. Twins and controls had nearly the same frequency of normal tests; however, the diabetic offspring had a significantly higher (P less than 0.001) prevalence of abnormal tests. These data suggest that magnitudes of environmental and genetic factors operating in monozygotic "pre-diabetic" children of diabetic parents.