In a pair of 19-year-old monozygotic twin girls, one developed insulin-dependent, ketosis-prone diabetes at the age of three and has required insulin for the past 16 years. Her identical twin has maintained normal oral and intravenous glucose tolerance with normal insulin release and glucagon suppression. An unequivocal hypertrophy of the muscle capillary basement membrane(1,800 ± 148 Å) was found in the diabetic twin, while a normal thickness of 1,149 ± 62 Å was present in her nondiabetic sister. Follow-up of the present subjects and data from other discordant identical twins who have reached adulthood could determine whether muscle capillary basement membrane hypertrophy is an independent marker of genetic diabetes in adults.

Discordance of diabetic microangiopathy in a pair of monozygotic twins has important implications regarding the influence of heredity and environment on diabetic microangiopathy.

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