Acanthosis nigricans in monozygotic twins with post receptor defects causing insulin resistance

Summary Two patients (monozygotic twins) presented with typical acanthosis nigricans of the neck, axillae and groin, without acral hypertrophy or signs of virilization. Histological features of the skin confirmed the diagnosis of acanthosis nigricans. Fasting blood glucose levels were normal. Insulin resistance was clinically asymptomatic. Plasma insulin levels after glucose or tolbutamide challenges and exogenous insulin tolerance tests were markedly abnormal. Insulin receptor antibodies were not detectable and insulin binding receptor concentration was slightly elevated on patient's red blood cells and fibroblasts. βLPH and plasma growth hormone levels were within normal limits. A post receptor defect was suspected to be the cause of insulin resistance. The authors conclude that insulin resistance and acanthosis nigricans may depend on a genetic basis and that insulin resistance may promote acanthosis nigricans in the absence of elevated growth-promoting peptides.