Search for variants of the gene-promoter and the potential phosphotyrosineencoding sequence of the insulin receptor substrate-2 gene: evaluation of their relation with alterations in insulin secretion and insulin sensitivity

Aims/hypothesis. The aim of this study was to screen part of the putative p romoter sequence in addition to 14 potential phosphotyrosine residues of hu man IRS-2 for genetic variability which might cause changes in protein expr ession or function. Furthermore, the potential impact on insulin secretion and sensitivity of a previously identified IRS-2 variant (Gly1057Asp) was a nalysed Methods. The screenings were carried out by the SSCP-heteroduplex technique on DNA from Type II (non-insulin-dependent) diabetic patients. The impact of the Gly1057Asp variant was analysed in four glucose-tolerant Scandinavia n study groups. Results. The results showed no nucleotide substitutions in the promoter seq uence, however, a novel heterozygous amino acid variant was identified (Leu 647-Val). In an association study, the new variant was found in 3 of 413 di abetic patents and in none of 280 glucose tolerant subjects. The variant di d not affect the binding of IRS-2 to the insulin receptor or p85 alpha of p hosphatidylinositol 3-kinase when measured in the yeast two-hybrid system. Examination of the common Gly1057Asp variant in 363 young healthy subjects and in 228 glucose tolerant offspring of one diabetic parent showed no diff erences in insulin secretion or insulin sensitivity after an intravenous gl ucose tolerance test. Glucose tolerant middle-aged subjects homozygous for the polymorphism (n = 31), however, had on average a 25% decrease in fastin g serum insulin concentrations (p = 0.009) and 28% (p = 0.01) and 34% (p = 0.003) reductions in serum insulin concentrations at 30 and 60 min, respect ively, during an OGTT compared with wildtype carriers (n = 107). In a cohor t of 639 elderly Swedish men the amino acid variant did not have any detect able impact on insulin secretion after an OGIT. Conclusion/interpretation. No genetic variability was found in the IRS-2 pr omoter. A rare IRS-2 variant at codon 647 has been identified in Type II di abetic patients. The prevalent codon 1057 polymorphism had no consistent ef fect on insulin secretion or insulin sensitivity.