Context: Intronic variants of TCF7L2 are confirmed genetic risk factors for type 2 diabetes and are associated to alterations in beta cell function in nondiabetic individuals.Objective: The objective of the study was to test whether TCF7L2 variability may affect beta-cell function also in patients with type 2 diabetes.Design: This was a cross-sectional association study.Setting: The study was conducted at a university hospital referral center for diabetes.Patients: Patients included 464 (315 males and 149 females) glutamic acid decarboxylase-negative patients [age: median 59 yr (interquartile range: 52-65); body mass index: 29.3 kg/m(2) (26.5-32.9); fasting plasma glucose: 7.0 mmol/liter (6.1-8.0)] with newly diagnosed type 2 diabetes.Intervention(s): Interventions included frequently sampled oral glucose tolerance test and euglycemic insulin clamp.Main Outcome Measure(s): beta-Cell function (derivative control and proportional control); insulin sensitivity; genotypes of the following TCF7L2 single-nucleotide polymorphisms: rs7901695, rs7903146, rs11196205, and rs12255372.Results: Both rs7901695 and rs7903146 diabetes risk alleles were associated with reduced proportional control of beta-cell function (P = 0.019 and P = 0.022, respectively). Two low-frequency haplotypes were associated with extreme (best and worst) phenotypes of beta-cell function (P < 0.01). No associations between TCF7L2 genotypes and insulin sensitivity were detected.Conclusions: TCF7L2 diabetesrisk variants, either as single-nucleotide polymorphisms or as haplotypes, detrimentally influence beta-cell function and might play a role in determining the metabolic phenotype of patients with newly diagnosed type 2 diabetes.
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