Insulin Resistance: Interactions Between Obesity and a Common Variant of Insulin Receptor substrate-1

Lancet. 1995 Aug 12;346(8972):397-402. doi: 10.1016/s0140-6736(95)92779-4.

Abstract

We previously discovered two aminoacid polymorphisms in codons 513 and 972 of the protein insulin receptor substrate-1 (IRS-1), which is important in cellular insulin action. We have investigated whether these polymorphisms are associated with changes in insulin sensitivity in a random sample of young healthy adults. Insulin sensitivity and secretion were measured during a combined intravenous glucose and tolbutamide tolerance test in 380 unrelated white subjects aged 18-32. IRS-1 polymorphisms were examined by single-strand conformation polymorphism and verified by restriction-enzyme digestion. No homozygous carrier of the codon-513 variant was identified, but one non-obese man had the codon-972 mutation on both alleles. He had low fasting-serum insulin and C-peptide concentrations and low insulin sensitivity and glucose effectiveness. During a 24 h dexamethasone test, he developed transient diabetes. In their heterozygous forms the codon-513 and codon-972 variants of IRS-1 were found in 3% and 9% of the subjects. Non-obese carriers of either polymorphism had similar insulin sensitivity and pancreatic beta-cell function to non-obese wild-type subjects (no known variants of IRS-1). Analysis of variance showed, however, a significant interaction between obesity (body-mass index > or = 25 kg/m2) and the heterozygous form of the codon-972 variant (p < 0.003); obese polymorphism carriers had lower insulin sensitivity than obese non-carriers (mean 6.0 [SD 3.3] vs 12.3 [9.5] x 10(-5) L min-1 pmol-1). The obese carriers of the codon-972 variant were also characterised by a clustering of metabolic cardiovascular risk factors, with raised fasting concentrations of plasma glucose, serum triglyceride, and plasma tissue-plasminogen-activator and its fast-acting inhibitor. With adjustment for known modulators of insulin sensitivity, multivariate analyses showed that the combination of obesity and the codon-972 variant was associated with a 50% reduction in insulin sensitivity (p = 0.0008). Our results suggest that the codon-972 IRS-1 gene variant may interact with obesity in the pathogenesis of common insulin-resistant disorders.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Codon / genetics
  • Dexamethasone
  • Female
  • Glucose Tolerance Test
  • Heterozygote
  • Humans
  • Insulin Receptor Substrate Proteins
  • Insulin Resistance*
  • Male
  • Mutation
  • Obesity / genetics*
  • Obesity / metabolism
  • Phosphoproteins / genetics*
  • Polymorphism, Genetic
  • Tolbutamide

Substances

  • Codon
  • IRS1 protein, human
  • Insulin Receptor Substrate Proteins
  • Phosphoproteins
  • Dexamethasone
  • Tolbutamide