👤 R R Frants

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

Type III hyperlipoproteinemia (HLP) is mainly found in homozygous apolipoprotein (APO) E2 (R158C) carriers. Genetic factors contributing to the expression of type III HLP were investigated in 113 hyper- and 52 normolipidemic E2/2 subjects, by testing for polymorphisms in APOC3, APOA5, HL (hepatic lipase) and LPL (lipoprotein lipase) genes. In addition, 188 normolipidemic Dutch control panels (NDCP) and 141 hypertriglyceridemic (HTG) patients were genotyped as well. No associations were found for four HL gene polymorphisms and two LPL gene polymorphisms and type III HLP. The frequency of the rare allele of APOC3 3238 G>C and APOA5 -1131 T>C (in linkage disequilibrium) was significantly higher in type III HLP patients when compared with normolipidemic E2/2 subjects, 15.6 vs 6.9% and 15.1 vs 5.8%, respectively, (P<0.05). Furthermore, the frequencies of the APOA5 c.56 G>C polymorphism and LPL c.27 G>A mutation were higher in type III HLP patients, though not significant. Some 58% of the type III HLP patients carried either the APOA5 -1131 T>C, c.56 G>C and/or LPL c.27 G>A mutation as compared to 27% of the normolipidemic APOE2/2 subjects (odds ratio 3.7, 95% confidence interval=1.8-7.5, P<0.0001). The HTG patients showed similar allele frequencies of the APOA5, APOC3 and LPL polymorphisms, whereas the NDCP showed similar allele frequencies as the normolipidemic APOE2/2. Patients with the APOC3 3238 G>C/APOA5 -1131 T>C polymorphism showed a more severe hyperlipidemia than patients without this polymorphism. Polymorphisms in lipolysis genes associate with the expression and severity of type III HLP in APOE2/2. Show less

The recently discovered apoAV is hypothesized to affect triglyceride metabolism by stimulating the lipolysis of triglycerides in VLDL and chylomicrons. We set out to determine the association between increased serum TG levels, plasma apoAV levels, and polymorphism of the APOA5 gene, with specific emphasis on the APOA5 S19W variation. This mutation alters the endoplasmic reticulum signal peptide and is hypothesized to impair apoAV secretion into the circulation. Two haplotype-tagging APOA5 polymorphisms, APOA5 S19W and APOA5 -1131T>C and plasma apoAV levels were determined in a population of patients with severe hypertriglyceridemia (HTG). As compared to a random control population, the allele frequencies of the APOA5 S19W and -1131T>C rare variants were significantly increased in HTG patients. Furthermore, the HTG population exhibited markedly elevated plasma apoAV levels that were positively correlated with serum TG levels. Plasma apoAV levels were positively correlated with occurrence of the APOA5 S19W rare variant. The increased allele frequencies of the APOA5 S19W and -1131T>C rare variants in the HTG population are in agreement with previous reports. Our data show a positive correlation between apoAV and TG levels. Moreover the finding of a positive association between apoAV levels and the APOA5 S19W rare variant is in disagreement with the hypothesis that this variant is poorly secreted. Show less

More than 90% of patients with type III hyperlipoproteinemia are homozygous carriers of the apolipoprotein (apo) E*2 allele. The great majority of these apoE2(Arg158-->Cys) homozygotes in the general population, however, are normolipidemic. Apparently, expression of the hyperlipidemic state requires additional genetic and/or environmental factors, suggesting a multifactorial etiology. To elucidate these additional risk factors, we analyzed normolipidemic and hyperlipidemic apoE2 homozygotes. Hyperinsulinemia was observed in 27 of 49 apoE2 homozygotes and associated with elevated lipid levels: hyperinsulinemic apoE2 homozygotes had type III hyperlipoproteinemia 6 times more often than apoE2 homozygotes with normal insulin levels (odds ratio 6.2, P=0.02). We screened the normolipidemic and hyperlipidemic apoE2 homozygotes for common variants in candidate genes involved in lipolysis-the APOA1-C3-A4 gene cluster, lipoprotein lipase, and hepatic lipase-and analyzed for associations with the expression of hyperlipidemia. In the hyperinsulinemic group, the 7 carriers of the SstI polymorphism (S2) in the APOC3 gene displayed severely elevated VLDL cholesterol (P(insulin by SstI)<0.001) and VLDL triglyceride (P(insulin by SstI)<0.01) and low levels of HDL (P(insulin by SstI)<0.02). In the normoinsulinemic group, no such relation of the SstI polymorphism with hyperlipidemia was observed. These data provide the first evidence for a combined effect of hyperinsulinemia and the SstI polymorphism on the expression of hyperlipidemia in apoE2 homozygotes. Show less

Hypertriglyceridaemia is a common metabolic disorder frequently found in patients with coronary heart disease. Numerous studies have revealed an association between the SstI polymorphism in the APOC3 gene and increased plasma apoC3 and triglyceride levels. In addition, two different variants within the promoter region have been recently suggested to be the mutations of the APOC3 gene leading to hypertriglyceridaemia. In the present study, we have applied haplotype analysis to investigate whether these promoter polymorphisms are involved in the lipid disorders of patients with distinct types of hypertriglyceridaemia: combined hyperlipidaemia (CHL), familial dysbetalipoproteinaemia (FD) and endogenous hypertriglyceridaemia (HTG). The -482 and -455 polymorphisms were significantly more frequent in FD patients (P = 0. 017) and endogenous HTG patients (P < 0.0001) than in CHL patients and a control group. The SstI polymorphism was only significantly more frequent in HTG patients (P < 0.0001). However, we did not find differences in frequencies for these polymorphisms in the APOC3 gene between CHL patients and a control group. Haplotype analysis indicates that the SstI polymorphism arose on the allele containing both promoter polymorphisms. The haplotype containing the SstI polymorphism is found five times more frequently among HTG patients (OR 5.28, 95% CI 1.65-16.90), which strongly suggests it is associated with an increased risk for severe hypertriglyceridaemia. Show less