Restriction-enzyme analysis of genomic DNA from 52 White and Hispanic nondiabetic subjects and 51 subjects with non-insulin-dependent diabetes (NIDDM) was carried out with insulin-receptor cDNA probes. A polymorphic 5.8-kilobase SstI fragment was found in 12 (23.5%) of 51 NIDDM subjects but only in 4 (7.7%) of 52 nondiabetic control subjects. This association is significant by χ2-analysis (P < .05). Furthermore, the nondiabetic subjects with the polymorphism were found to have hyperinsulinemia and/or nondiagnostic glucose tolerance. The polymorphism is a genetic marker for a phenotype that is neither necessary nor, by itself, sufficient for NIDDM. Nevertheless, it may indicate that insulin resistance functionally related to an insulin-receptor gene polymorphism is the proximal cause of NIDDM in at least one subset of the population.

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