Diabetes-Associated Variation in TCF7L2 Is Associated with a Longitudinal Decline in Glucose Tolerance Accompanied by Impaired Suppression of Postprandial Glucagon Secretion

Diabetes-associated alleles in TCF7L2 increase the rate of conversion from prediabetes to type 2 diabetes (T2DM). Multiple studies have shown an association of the T allele at rs7903146 with impaired β-cell function and more recently with defective suppression of α-cell secretion by glucose. However, the temporal relationship of these abnormalities is uncertain. To study the longitudinal changes in islet function, we recruited 140 individuals half of whom were homozygous for the diabetes-associated allele (TT) at rs7903146. The remainder were homozygous for the protective allele (CC). Subjects were studied on 2 occasions, 3 years apart using an oral 75g glucose challenge. This was labelled with 13C-glucose, in concert with intravenously infused tracers to enable measurement of endogenous glucose production, meal appearance and glucose disposal. Indices for insulin secretion and action were estimated using the oral minimal model. Fasting, peak and integrated (443 ± 27 vs. 428 ± 50 mmol/l per 6hr, p = 0.54) post-prandial glucose concentrations did not differ over time in people with the CC genotype. In contrast, post-prandial integrated glucose concentrations increased (441 ± 29 vs. 544 ± 37 mmol/l per 6hr, p < 0.01) in people with the TT genotype. This was accompanied by an increase in integrated postprandial glucagon concentrations (526 ± 39 vs. 618 ± 61 pmol/l per 2hr, p = 0.04) that was not observed in the CC genotype (537 ± 50 vs. 525 ± 65 pmol/l per 2hr, p = 0.07). There were no baseline differences in β-cell function between genotype groups. Disposition Index in both TT (950 ± 130 vs. 868 ± 92 10-4 dl/kg/min per μU/ml, baseline vs. follow-up study respectively, p=0.42) and CC (896 ± 177 vs. 1062 ± 289 10-4 dl/kg/min per μU/ml, p=0.65) groups did not change. This data would suggest that α-cell dysfunction associated with the TT genotype (rs7903146) precedes β-cell dysfunction in people prior to the development of T2DM. Disclosure M.Zeini: None. K.Muthusamy: None. A.M.Egan: None. M.C.Laurenti: None. C.Cobelli: None. C.Dalla man: Research Support; Sanofi-Aventis Deutschland GmbH, Becton, Dickinson and Company. A.Vella: Advisory Panel; Rezolute, Inc., Consultant; Crinetics Pharmaceuticals, Inc., Hanmi Pharm. Co., Ltd., Zealand Pharma A/S, Other Relationship; Novo Nordisk. Funding National Institutes of Health (DK116723)