FREQUENCY OF MUTATIONS OF INSULIN-RECEPTOR GENE IN JAPANESE PATIENTS WITH NIDDM

To examine the prevalence of abnormalities in the insulin receptor structure gene in Japanese patients with noninsulin-dependent diabetes mellitus (NIDDM), a population of 51 patients with NIDDM was screened for mutations in this gene, Patient genomic DNAs of both alleles corresponding to 22 exons of the gene were amplified by polymerase chain reaction (PCR), The PCR products on pUC19 were sequenced. Three patients with heterozygous missense mutation Thr(831) --> Ala(831) in exon 13 and one patient with heterozygous missense mutation Tyr(1334) --> Cys(1334) in exon 22 of the beta-subunits mere identified, Linkage analysis of one of the families plus statistical studies showed that the mutation Thr(831) --> Ala(831) is possibly responsible for the onset of NIDDM, In COS cells transiently expressing both mutant receptor cDNAs and a cDNA of a M(r) 85,000 regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase), the mutation Tyr(1334) --> Cys(1334) impaired binding of the receptor with the M(r), 85,000 subunit of PI 3-kinase, but linkage analysis of the family showed that the mutation did not cosegregate with NIDDM in the pedigree. Therefore, one missense mutation (Thr(831) --> Ala(831)) in the insulin receptor, as found in three patients, is possibly involved in the etiology of a subset of the 51 NIDDM patients.