title: Complex haplotypes of IRS2 gene are associated with severe obesity and reveal heterogeneity in the effect of Gly1057Asp mutation.
abstract: In order to understand the role of the insulin receptor substrate-2 (IRS2) gene (chromosome region: 13q34) in obesity, a complex disorder associated with insulin resistance and glucose intolerance, we determined single nucleotide polymorphims (SNPs) and complex haplotypes in women with morbid obesity and a body mass index (BMI) of 41+/-0.8 kg/m2 ( n=99) compared with controls having a BMI of 23.8+/-0.1 kg/m2 ( n=92). Sequencing of unphased DNA or digestion of polymerase chain reaction fragments revealed seven SNPs, including a new C/T(-769) replacement at the 5' untranslated region. Considering four or seven SNPs, we reconstructed with the PHASE program nine or 24 haplotypes, respectively, that were well correlated into the cladogram. Logistic regression analysis with nine haplotypes in the whole sample revealed that obesity was associated with haplotype H3, with P<0.025, an odds ratio (OR) of 1.9 and a 95% confidence interval (CI) of 1.1-3.4, or pairs 3/3 ( P<0.005, OR=8.7, CI=1.9-40.1) and 3/4 ( P<0.023, OR=2.5, CI=1.1-5.6), all containing the the Gly1057Asp allelic variant of IRS2, whereas controls were associated with H5 and H6 ( P<0.02, OR=0.2, CI=0.01-0.81). Although obese H5 carriers (also containing Gly1057Asp mutation) were the most insulin resistant, haplotypes of IRS2 were poorly correlated (analysis of variance) with insulin resistance. By contrast, haplotypes H3, H4 and pairs 3/3 were consistently associated with increased 2-h glucose levels during an oral glucose tolerance test in obese individuals ( P<0.0005, 0.025 and 0.027, respectively). These data indicate that IRS2 is an influential gene in severe obesity and glucose intolerance in this population, whereas gene-based haplotypes of IRS2 have revealed heterogeneity in the behaviour of the Gly1057Asp mutation in relation to insulin resistance.
authors.affiliation: Molecular Endocrinology Laboratory, University Institute of Clinical Research, Faculty of Medicine, 641 Avenue du Doyen Gaston Giraud, 34093, Montpellier Cedex 5, France.
authors.forename: Corinne
authors.initials: C
authors.lastname: Lautier
authors.forename: Samira Ait
authors.initials: SA
authors.lastname: El Mkadem
authors.forename: Eric
authors.initials: E
authors.lastname: Renard
authors.forename: Jean Frédéric
authors.initials: JF
authors.lastname: Brun
authors.forename: Jean Christophe
authors.initials: JC
authors.lastname: Gris
authors.forename: Jacques
authors.initials: J
authors.lastname: Bringer
authors.forename: Florin
authors.initials: F
authors.lastname: Grigorescu
mesh_terms: D000328:Adult; D000483:Alleles; D001786:Blood Glucose; D015992:Body Mass Index; D016022:Case-Control Studies; D005260:Female; D014644:Genetic Variation / Q000235:genetics*; D005838:Genotype; D018149:Glucose Intolerance / Q000235:genetics*; D005951:Glucose Tolerance Test; D006239:Haplotypes; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000235:genetics*; D047908:Intracellular Signaling Peptides and Proteins; D009765:Obesity / Q000235:genetics*; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics*; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011972:Receptor, Insulin / Q000235:genetics
chemical_list: D001786:Blood Glucose; C526297:IRS2 protein, human; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D011972:Receptor, Insulin