In the other mutant allele, there is a missense mutation substituting serine for Asn462-a mutation identified previously in one allele of the insulin receptor gene in a patient with type-A insulin resistance.
These observations suggest that the homozygous Arg252-->His mutation is responsible for the type A insulin resistance of the proband, whereas in the heterozygous state, the mutation results in mild insulin resistance indistinguishable from that observed in noninsulin-dependent diabetes mellitus.