BACKGROUND: T2D susceptibility genes identified so far are mainly involved in beta-cell function. Studies from GWAS have identified many loci but were focused on simple clinical parameters. The missing heritability in T2D might be explained by multiple, low-frequency variants that GWAS let slip. A powerful approach to discover causal variants is sequencing the extremes of phenotypes by Next Generation Sequencing (NGS).
AIMS: To identify new low-frequency variants in GWAS loci for T2D, searching for primary defects in beta-cell insulin secretion through two stages. Stage 1: re-sequencing of 9 candidate genes from GWAS (p
METHODOLOGY: We have a large population (996 adults and 896 youths), and we aim to enroll up to 2500 subjects to amplify the power for genetic association. In all subjects measures of insulin secretion and resistance from OGTT have been calculated, including insulinogenic index (IGI30), ISI (insulin-sensitivity index), and Disposition Index (DI). NGS is performed by TruSeqCustomAmplicon library on MiSeq system (Illumina). New variants will be genotyped by Real-Time PCR.
RELEVANCE OF EXPECTED RESULTS: The novelty of this approach is the analysis of extremes of quantitative traits rather than dichotomizing the same distribution into cases and controls, comparing the low and the high ends of the normal distribution, to maximize the statistical power to discover low-frequency variants that contribute to traits. We expect that this study will deliver several results: from confirmatory gene association to newer T2D associated polymorphisms, to possible new insights into potential biological mechanisms influencing T2D pathogenesis.
