Variants and haplotypes of TCF7L2 are associated with β-cell function in patients with newly diagnosed type 2 diabetes: the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS) 1.

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 β-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): β-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 β-cell function (P = 0.019 and P = 0.022, respectively). Two low-frequency haplotypes were associated with extreme (best and worst) phenotypes of β-cell function (P < 0.01). No associations between TCF7L2 genotypes and insulin sensitivity were detected.
CONCLUSIONS: TCF7L2 diabetes risk variants, either as single-nucleotide polymorphisms or as haplotypes, detrimentally influence β-cell function and might play a role in determining the metabolic phenotype of patients with newly diagnosed type 2 diabetes.