No cases of diabetes, impaired glucose tolerance, and acanthosis nigricans; lower fasting glucose in subjects <30 years old vs controls; HbA1c insignificantly higher in patients ≥30 than <30 years old; increased area under the curve for insulin in oral glucose tolerance test in all patients; higher 2-hour insulin in patients ≥30 years old vs controls; higher area under the curve for insulin after oral glucose load in I172N group vs controls and vs null and I2G genotypes. The gene discussed is INS; the disease is acanthosis nigricans.