THOC5: a novel gene involved in HDL-cholesterol metabolism.

Although numerous genes are known to regulate serum lipid traits, identified variants explain only a small proportion of the expected heritability. We intended to identify further genetic variants associated with lipid phenotypes in a self-contained population of Sorbs in Germany. We performed a genome-wide association study (GWAS) on LDL-cholesterol, HDL-cholesterol (HDL-C), and triglyceride (TG) levels in 839 Sorbs. All single-nucleotide polymorphisms with a P value <0.01 were subjected to a meta-analysis, including an independent Swedish cohort (Diabetes Genetics Initiative; n = ∼3,100). Novel association signals with the strongest effects were subjected to replication studies in an additional German cohort (Berlin, n = 2,031). In the initial GWAS in the Sorbs, we identified 14 loci associated with lipid phenotypes reaching P values <10⁻5 and confirmed significant effects for 18 previously reported loci. The combined meta-analysis of the three study cohorts (n(HDL) = 6041; n(LDL) = 5,995; n(TG) = 6,087) revealed a novel association for a variant in THOC5 (rs8135828) with serum HDL-C levels (P = 1.78 × 10⁻7; Z-score = -5.221). Consistently, the variant was also associated with circulating APOA1 levels in Sorbs. The small interfering RNA-mediated mRNA silencing of THOC5 in HepG2 cells resulted in lower mRNA levels of APOA1, SCARB1, and ABCG8 (all P < 0.05). We propose THOC5 to be a novel gene involved in the regulation of serum HDL-C levels.

Genetic variation in GPR133 is associated with height: genome wide association study in the self-contained population of Sorbs.

Recently, associations of several common genetic variants with height have been reported in different populations. We attempted to identify further variants associated with adult height in a self-contained population (the Sorbs in Eastern Germany) as discovery set. We performed a genome wide association study (GWAS) (approximately 390,000 genetic polymorphisms, Affymetrix gene arrays) on adult height in 929 Sorbian individuals. Subsequently, the best SNPs (P < 0.001) were taken forward to a meta-analysis together with two independent cohorts [Diabetes Genetics Initiative, British 1958 Birth Cohort, (58BC, publicly available)]. Furthermore, we genotyped our best signal for replication in two additional German cohorts (Leipzig, n = 1044 and Berlin, n = 1728). In the primary Sorbian GWAS, we identified 5 loci with a P-value < 10(-5) and 455 SNPs with P-value < 0.001. In the meta-analysis on those 455 SNPs, only two variants in GPR133 (rs1569019 and rs1976930; in LD with each other) retained a P-value at or below 10(-6) and were associated with height in the three cohorts individually. Upon replication, the SNP rs1569019 showed significant effects on height in the Leipzig cohort (P = 0.004, beta = 1.166) and in 577 men of the Berlin cohort (P = 0.049, beta = 1.127) though not in women. The combined analysis of all five cohorts (n = 6,687) resulted in a P-value of 4.7 x 10(-8) (beta = 0.949). In conclusion, our GWAS suggests novel loci influencing height. In view of the robust replication in five different cohorts, we propose GPR133 to be a novel gene associated with adult height.

Effects of genetic variation in the visfatin gene (PBEF1) on obesity, glucose metabolism, and blood pressure in children.

Visfatin is a peptide predominantly expressed in visceral adipose tissue and was hypothesized to be related to obesity and insulin resistance. In the present study, we investigated the effects of genetic variations in the visfatin gene (pre-B-cell colony-enhancing factor 1 [PBEF1]) on obesity, metabolic parameters, and blood pressure (BP) in 2 children cohorts. We genotyped 3 representative single nucleotide polymorphisms (rs9770242, -948G>T, rs4730153) in 731 schoolchildren and in an independent cohort of 167 obese children. There was no association of any of the 3 polymorphisms or their haplotypes with body mass index (BMI), waist-to-hip ratio, or parameters of glucose, insulin, or lipid metabolism in either cohort. However, the -948G variant was associated with significantly higher diastolic BP in obese children (P < .05 after adjusting for age, sex, pubertal stage, and height). Haplotype analyses confirmed the [T-G-A] haplotype to be significantly related to increased diastolic BP in both schoolchildren and obese children. In conclusion, genetic variants in PBEF1 may be associated with increased BP in children but are not likely to contribute significantly to the variation in body mass index and glucose, insulin, or lipid metabolism.

ENPP1 variants and haplotypes predispose to early onset obesity and impaired glucose and insulin metabolism in German obese children.

CONTEXT: ENPP1 (nucleotide pyrophosphatase/phosphodiesterase-1) encodes a membrane-bound glycoprotein that inhibits the insulin-receptor tyrosine kinase activity, resulting in reduced insulin sensitivity. Hence, variants in this gene may be related to obesity and insulin resistance. OBJECTIVE: Therefore, in this study, we aimed to explore the role of ENPP1 genetic variants in obesity and related traits in a representative population of Caucasian children and in cohorts of obese children with detailed metabolic characteristics including oral glucose tolerance test. DESIGN: We genotyped the K121Q, IVS20delT-11, and A/G+1044TGA ENPP1 genetic variants for association analyses in 712 schoolchildren (346 boys and 366 girls; mean age 12 +/- 3 yr; mean body mass index-sd score 0.09 +/- 0.04) and in independent cohorts of 205 obese children from Leipzig and 195 obese children from Datteln, Germany. RESULTS: We identified a significantly increased risk of obesity in Leipzig children carrying the 121Q variant (adjusted odds ratio, 1.82; 95% confidence interval, 1.30-2.56; P = 0.0005) or the [Q-delT-G] haplotype [1.75 (1.17-2.62), P = 0.006] as compared with a lean control group. This was replicated in another independent obesity/overweight cohort from Leipzig as well as obese children from Datteln. In addition, obese children from Leipzig with the [Q-delT-G] haplotype were characterized by impaired glucose metabolism, whereas the [K-delT-G] and [K-insT-A] haplotypes were significantly associated with improved insulin sensitivity and glucose metabolism (all P < 0.05 after adjusting for age, gender, and body mass index). CONCLUSIONS: In conclusion, our study suggests a potential role of the K121Q polymorphism or derived ENPP1 haplotypes in increased susceptibility to obesity and early impairment of glucose and insulin metabolism in children.

Genetic variation in the visfatin gene (PBEF1) and its relation to glucose metabolism and fat-depot-specific messenger ribonucleic acid expression in humans.

CONTEXT AND OBJECTIVE: Visfatin is a peptide suggested to play a role in glucose homeostasis. In the present study, we investigated the role of genetic variation in the visfatin gene in the pathophysiology of obesity/type 2 diabetes mellitus (T2DM). DESIGN: The visfatin gene (PBEF1) was sequenced in DNA samples from 24 nonrelated Caucasian subjects. Identified genetic variants were used for association analyses of T2DM in a case-control study (503 diabetic subjects and 476 healthy controls) and T2DM-related traits in 626 nondiabetic subjects. The effect of genetic variation in the visfatin gene on its mRNA expression in a subgroup of 157 nondiabetic subjects with measurements of visfatin mRNA expression in visceral and sc fat depots was also analyzed. RESULTS: Seven single-nucleotide polymorphisms (SNPs) and one insertion/deletion were identified. Three SNPs (rs9770242, -948G-->T, rs4730153) that were representatives of their linkage disequilibrium groups were genotyped in Caucasians from Germany with a wide range of body fat distribution and insulin sensitivity for association analyses. No association of T2DM with any of the genotyped SNPs or their haplotypes was found. However, the ratio of visceral/sc visfatin mRNA expression was associated with all three genetic polymorphisms (P < 0.05). Moreover, the -948G-->T variant was associated with 2-h plasma glucose and fasting insulin concentrations (P < 0.05) in nondiabetic subjects. CONCLUSIONS: In conclusion, our data suggest that genetic variation in the visfatin gene may have a minor effect on visceral and sc visfatin mRNA expression profiles but does not play a major role in the development of obesity or T2DM.

Role of genetic variation in the human sodium-glucose cotransporter 2 gene (SGLT2) in glucose homeostasis.

AIMS: Mutations in the sodium-glucose cotransporter 2 (SGLT2), as well as treatment with SGLT2 inhibitors result in reduced fasting glucose levels, HbA(1c) and BMI. We therefore investigated the effects of common genetic variation in SGLT2 on human Type 2 diabetes and related traits. MATERIALS & METHODS: Four HapMap tagging SNPs covering the common genetic variation in SGLT2 (r² > 0.8 and minor allele frequency > 0.01) were genotyped for subsequent association studies on BMI, Type 2 diabetes and related metabolic traits in 1013 Sorbs (Germany). An independent cohort from Berlin (n = 2042) was taken for replication. RESULTS: The rs9934336 G-allele was nominally associated with increased 30-min plasma glucose, 120-min insulin concentrations and AUC120min(glucose) during oral glucose tolerance test in 907 nondiabetic Sorbs (p < 0.05). In the combined analysis including the Sorbs and the Berlin cohort, rs9934336 was nominally associated with 120-min insulin concentrations (adjusted p < 0.05) in nondiabetic subjects (n = 2590). CONCLUSION: Our data suggest a role of SGLT2 genetic variation in the regulation of glucose homeostasis and promote pharmacogenomic studies to clarify the efficacy of antidiabetic treatment by SGLT2 inhibitors.

Genetic and evolutionary analyses of the human bone morphogenetic protein receptor 2 (BMPR2) in the pathophysiology of obesity.

OBJECTIVE: Human bone morphogenetic protein receptor 2 (BMPR2) is essential for BMP signalling and may be involved in the regulation of adipogenesis. The BMPR2 locus has been suggested as target of recent selection in human populations. We hypothesized that BMPR2 might have a role in the pathophysiology of obesity. RESEARCH DESIGN AND METHODS: Evolutionary analyses (dN/dS, Fst, iHS) were conducted in vertebrates and human populations. BMPR2 mRNA expression was measured in 190 paired samples of visceral and subcutaneous adipose tissue. The gene was sequenced in 48 DNA samples. Nine representative single nucleotide polymorphisms (SNPs) were genotyped for subsequent association studies on quantitative traits related to obesity in 1830 German Caucasians. An independent cohort of 925 Sorbs was used for replication. Finally, relation of genotypes to mRNA in fat was examined. RESULTS: The evolutionary analyses indicated signatures of selection on the BMPR2 locus. BMPR2 mRNA expression was significantly increased both in visceral and subcutaneous adipose tissue of 37 overweight (BMI>25 and <30 kg/m²) and 80 obese (BMI>30 kg/m²) compared with 44 lean subjects (BMI< 25 kg/m²) (P<0.001). In a case-control study including lean and obese subjects, two intronic SNPs (rs6717924, rs13426118) were associated with obesity (adjusted P<0.05). Combined analyses including the initial cohort and the Sorbs confirmed a consistent effect for rs6717924 (combined P = 0.01) on obesity. Moreover, rs6717924 was associated with higher BMPR2 mRNA expression in visceral adipose tissue. CONCLUSION: Combined BMPR2 genotype-phenotype-mRNA expression data as well as evolutionary aspects suggest a role of BMPR2 in the pathophysiology of obesity.

Effect of genetic variation in the human fatty acid synthase gene (FASN) on obesity and fat depot-specific mRNA expression.

Inhibition of fatty acid synthase (FASN) induces a rapid decline in fat stores in mice, suggesting a role for this enzyme in energy homeostasis. To investigate the potential role of FASN in the pathophysiology of human obesity, the FASN gene was sequenced in 48 German whites. Thirty-five single-nucleotide polymorphisms (SNPs) were identified. Eight SNPs representative for their linkage disequilibrium groups and the Val1483Ile (rs2228305) substitution were genotyped for subsequent association analyses in 1,311 adults from Germany. Further, the tagging SNPs were genotyped also in German childhood cohorts (738 schoolchildren, 205 obese children). Effects of genetic variation on FASN mRNA expression in visceral and subcutaneous adipose tissue from a subgroup of 172 subjects were analyzed. Several polymorphisms in the FASN (rs62078748, rs2229422, rs2229425, and rs17848939) were nominally associated with obesity in case-control studies including 446 obese subjects (BMI >or=30 kg/m(2)) and 389 lean controls (BMI

Role of genetic variation in the cannabinoid type 1 receptor gene (CNR1) in the pathophysiology of human obesity.

AIMS: The endocannabinoid system may contribute to the association of visceral fat accumulation with metabolic diseases. Here we investigated the effects of genetic variation in the cannabinoid type 1 receptor gene (CNR1) on its mRNA expression in adipose tissue from visceral and subcutaneous depots and on the development of obesity. MATERIALS & METHODS: CNR1 was sequenced in 48 nonrelated German Caucasians to detect genetic variation. Five representative variants including HapMap tagging SNPs (rs12720071, rs806368, rs806370, rs1049353 and rs806369) were genotyped for subsequent association studies in two independent cohorts (total n = 2774) with detailed metabolic testing: subjects from the Leipzig Study (n = 1857) and a self-contained population of Sorbs from Germany (n = 917). RESULTS: In a case-control study of lean (BMI <25 kg/m(2)) versus obese (BMI >30 kg/m(2)) subjects, rs806368 was found to be nominally associated with obesity in the Sorbian cohort (adjusted p < 0.05), but not in the Leipzig cohort. Also, several SNPs (rs806368, rs806370 and rs12720071) were nominally associated with serum leptin levels (p < 0.05 after adjusting for age, sex and BMI). However, none of these associations remained significant after accounting for multiple testing. Furthermore, none of the SNPs were related to CNR1 mRNA expression in visceral and subcutaneous fat. CONCLUSION: The data suggest that common genetic variation in the CNR1 gene does not influence mRNA expression in adipose tissue nor does it play a significant role in the pathophysiology of obesity in German and Sorbian populations.

Association of FTO variants with BMI and fat mass in the self-contained population of Sorbs in Germany.

The association between common variants in the FTO gene with weight, adiposity and body mass index (BMI) has now been widely replicated. Although the causal variant has yet to be identified, it most likely maps within a 47 kb region of intron 1 of FTO. We performed a genome-wide association study in the Sorbian population and evaluated the relationships between FTO variants and BMI and fat mass in this isolate of Slavonic origin resident in Germany. In a sample of 948 Sorbs, we could replicate the earlier reported associations of intron 1 SNPs with BMI (eg, P-value=0.003, beta=0.02 for rs8050136). However, using genome-wide association data, we also detected a second independent signal mapping to a region in intron 2/3 about 40-60 kb away from the originally reported SNPs (eg, for rs17818902 association with BMI P-value=0.0006, beta=-0.03 and with fat mass P-value=0.0018, beta=-0.079). Both signals remain independently associated in the conditioned analyses. In conclusion, we extend the evidence that FTO variants are associated with BMI by putatively identifying a second susceptibility allele independent of that described earlier. Although further statistical analysis of these findings is hampered by the finite size of the Sorbian isolate, these findings should encourage other groups to seek alternative susceptibility variants within FTO (and other established susceptibility loci) using the opportunities afforded by analyses in populations with divergent mutational and/or demographic histories.

Adipose tissue expression and genetic variants of the bone morphogenetic protein receptor 1A gene (BMPR1A) are associated with human obesity.

OBJECTIVE: Members of the family of bone morphogenetic proteins (BMPs) are important regulators of adipogenesis. We examined the role of the BMP receptor 1A gene (BMPR1A) in the pathophysiology of human obesity. RESEARCH DESIGN AND METHODS: We measured BMPR1A mRNA expression in paired samples of visceral and subcutaneous adipose tissue from 297 subjects and sequenced the BMPR1A in 48 nonrelated white subjects. Twenty-one representative variants including HapMap tagging single nucleotide polymorphisms (SNPs) were then genotyped for association studies in German whites (n = 1,907). For replication analyses, we used a population of Sorbs from Germany (n = 900) and German childhood cohorts (n = 1,029 schoolchildren and 270 obese children). RESULTS: mRNA expression of the BMPR1A was significantly increased in both visceral and subcutaneous adipose tissue of overweight and obese subjects compared with lean subjects (P < 0.05). In a case-control study, four SNPs (rs7095025, rs11202222, rs10788528, and rs7922846) were nominally associated with obesity (adjusted P < 0.05). For three SNPs (rs7095025, rs11202222, and rs10788528), the association with obesity was confirmed in the independent cohort of Sorbs (adjusted P < 0.005). Consistent with this, BMPR1A SNPs were nominally associated with obesity-related quantitative traits in nondiabetic subjects in both adult cohorts. Furthermore, homozygous carriers of the obesity risk alleles had higher BMPR1A mRNA expression in fat than noncarriers. CONCLUSIONS: Our data suggest that genetic variation in the BMPR1A may play a role in the pathophysiology of human obesity, possibly mediated through effects on mRNA expression.

Effects of genetic variation in the human retinol binding protein-4 gene (RBP4) on insulin resistance and fat depot-specific mRNA expression.

OBJECTIVE: Serum retinol binding protein 4 (RBP4) is a new liver- and adipocyte-derived signal that may contribute to insulin resistance. Therefore, the RBP4 gene represents a plausible candidate gene involved in susceptibility to type 2 diabetes. RESEARCH DESIGN AND METHODS: In this study, the RBP4 gene was sequenced in DNA samples from 48 nonrelated Caucasian subjects. Five novel and three known single nucleotide polymorphisms (SNPs) were identified. Furthermore, five recently reported SNPs were genotyped in 90 subjects. Six SNPs, representative of their linkage disequilibrium groups, were then genotyped in 934 diabetic and 716 nondiabetic subjects. RESULTS: A haplotype of six common SNPs (A-G-G-T-G-C) was significantly increased in 934 case subjects with type 2 diabetes compared with 537 healthy control subjects with normal glucose tolerance (P = 0.02; odds ratio 1.37 [95% CI 1.05-1.79]). Furthermore, in the cohort of 716 nondiabetic Caucasian subjects, carriers of the A-G-G-T-G-C haplotype had significantly higher mean fasting plasma insulin and 2-h plasma glucose than subjects without the haplotype. Two single SNPs (rs10882283 and rs10882273) were also associated with BMI, waist-to-hip ratio, and fasting plasma insulin, and several SNPs were associated with circulating free fatty acids (all adjusted P < 0.05). In addition, subjects carrying a previously reported diabetes-associated haplotype had significantly higher mRNA levels in visceral adipose tissue (adjusted P < 0.05) in a subgroup of nondiabetic subjects (n = 170) with measurements of RBP4 mRNA expression in visceral and subcutaneous fat depots. CONCLUSIONS: Our data indicate a role of RBP4 genetic variation in susceptibility to type 2 diabetes and insulin resistance, possibly through an effect on RBP4 expression.