Gene variants in the novel type 2 diabetes loci CDC123/CAMK1D, THADA, ADAMTS9, BCL11A, and MTNR1B affect different aspects of pancreatic [beta]-cell function

OBJECTIVE--Recently, results from a meta-analysis of genome-wide association studies have yielded a number of novel type 2 diabetes loci. However, conflicting results have been published regarding their effects on insulin secretion and insulin sensitivity. In this study we used hyperglycemic clamps with three different stimuli to test associations between these novel loci and various measures of [beta]-cell function. RESEARCH DESIGN AND METHODS--For this study, 336 participants, 180 normal glucose tolerant and 156 impaired glucose tolerant, underwent a 2-h hyperglycemic clamp. In a subset we also assessed the response to glucagon-like peptide (GLP)-1 and arginine during an extended clamp (n = 123). All subjects were genotyped for gene variants in JAZF1, CDC123/ CAMK1D, TSPAN8/LGR5, THADA, ADAMTS9, NOTCH2/ ADAMS30, DCD, VEGFA, BCL11A, HNF1B, WFS1, and MTNR1B. RESULTS--Gene variants in CDC123/CAMK1D, ADAMTS9, BCL11A, and MTNR1B affected various aspects of the insulin response to glucose (all P < 6.9 x [10.sup.-3]). The THADA gene variant was associated with lower [beta]-cell response to GLP-1 and arginine (both P < 1.6 x [10.sup.-3]), suggesting lower [beta]-cell mass as a possible pathogenic mechanism. Remarkably, we also noted a trend toward an increased insulin response to GLP-1 in carriers of MTNRIB (P = 0.03), which may offer new therapeutic possibilities. The other seven loci were not detectably associated with [beta]-cell function. CONCLUSIONS--Diabetes risk alleles in CDC123/CAMK1D, THADA, ADAMTS9, BCL11A, and MTNR1B are associated with various specific aspects of [beta]-cell function. These findings point to a clear diversity in the impact that these various gene variants may have on (dys)function of pancreatic [beta]-cells.
Genome-wide association (GWA) studies have revealed a large number of novel type 2 diabetes susceptibility loci (1-4). Most of the genes identified during the first wave of GWA study results [...]