Glucose levels 2 h after an oral glucose challenge are a clinical measure of glucose tolerance used in the diagnosis of type 2 diabetes. We report a meta-analysis of nine genome-wide association studi Show more
Glucose levels 2 h after an oral glucose challenge are a clinical measure of glucose tolerance used in the diagnosis of type 2 diabetes. We report a meta-analysis of nine genome-wide association studies (n = 15,234 nondiabetic individuals) and a follow-up of 29 independent loci (n = 6,958-30,620). We identify variants at the GIPR locus associated with 2-h glucose level (rs10423928, beta (s.e.m.) = 0.09 (0.01) mmol/l per A allele, P = 2.0 x 10(-15)). The GIPR A-allele carriers also showed decreased insulin secretion (n = 22,492; insulinogenic index, P = 1.0 x 10(-17); ratio of insulin to glucose area under the curve, P = 1.3 x 10(-16)) and diminished incretin effect (n = 804; P = 4.3 x 10(-4)). We also identified variants at ADCY5 (rs2877716, P = 4.2 x 10(-16)), VPS13C (rs17271305, P = 4.1 x 10(-8)), GCKR (rs1260326, P = 7.1 x 10(-11)) and TCF7L2 (rs7903146, P = 4.2 x 10(-10)) associated with 2-h glucose. Of the three newly implicated loci (GIPR, ADCY5 and VPS13C), only ADCY5 was found to be associated with type 2 diabetes in collaborating studies (n = 35,869 cases, 89,798 controls, OR = 1.12, 95% CI 1.09-1.15, P = 4.8 x 10(-18)). Show less
A meta-analysis of 21 genome-wide association studies identified 11 novel genetic loci implicated in fasting glucose homeostasis. We aimed to evaluate the impact of these variants on insulin release a Show more
A meta-analysis of 21 genome-wide association studies identified 11 novel genetic loci implicated in fasting glucose homeostasis. We aimed to evaluate the impact of these variants on insulin release and insulin sensitivity estimated from OGTTs. Eleven variants in or near DGKB/TMEM195, ADCY5, MADD, ADRA2A, FADS1, CRY2, SLC2A2, GLIS3, PROX1, C2CD4B and IGF1 were genotyped in 6,784 middle-aged participants of the population-based Inter99 cohort. Association studies of quantitative estimates of insulin release and insulin sensitivity were performed in 5,722 non-diabetic Danish participants on whom an OGTT was performed. Assuming an additive genetic model, carriers of the alleles increasing fasting glucose in DGKB/TMEM195, ADRA2A, GLIS3 and C2CD4B showed decreased glucose-stimulated insulin release as assessed by the BIGTT-acute insulin response index (2.7-3.5%; p < 0.005 for all) and by corrected insulin response (2.8-5.9%; p < 0.03 for all). In addition, the PROX1 glucose-raising allele showed a 2.9% decreased corrected insulin response (p = 0.03), while the hyperglycaemic allele of variants in or near ADRA2A, FADS1, CRY2 and C2CD4B were associated with a 2.6% to 9.3% decrease in one or both of two different OGTT-based disposition indices (p < 0.02 for all). After correction for multiple testing, variants in the DGKB/TMEM195, ADRA2A, GLIS3 and C2CD4B loci were associated with estimates of beta cell function. We found that the lead variants at the DGKB/TMEM195, ADRA2A, GLIS3 and C2CD4B loci were associated with decreased glucose-stimulated insulin response. This association underlines the importance of pancreatic beta cell dysfunction in the genetic predisposition to hyperglycaemia and type 2 diabetes. Show less
Levels of circulating glucose are tightly regulated. To identify new loci influencing glycemic traits, we performed meta-analyses of 21 genome-wide association studies informative for fasting glucose, Show more
Levels of circulating glucose are tightly regulated. To identify new loci influencing glycemic traits, we performed meta-analyses of 21 genome-wide association studies informative for fasting glucose, fasting insulin and indices of beta-cell function (HOMA-B) and insulin resistance (HOMA-IR) in up to 46,186 nondiabetic participants. Follow-up of 25 loci in up to 76,558 additional subjects identified 16 loci associated with fasting glucose and HOMA-B and two loci associated with fasting insulin and HOMA-IR. These include nine loci newly associated with fasting glucose (in or near ADCY5, MADD, ADRA2A, CRY2, FADS1, GLIS3, SLC2A2, PROX1 and C2CD4B) and one influencing fasting insulin and HOMA-IR (near IGF1). We also demonstrated association of ADCY5, PROX1, GCK, GCKR and DGKB-TMEM195 with type 2 diabetes. Within these loci, likely biological candidate genes influence signal transduction, cell proliferation, development, glucose-sensing and circadian regulation. Our results demonstrate that genetic studies of glycemic traits can identify type 2 diabetes risk loci, as well as loci containing gene variants that are associated with a modest elevation in glucose levels but are not associated with overt diabetes. Show less