Stefan Coassin

SLC2A9 influences uric acid concentrations with pronounced sex-specific effects

Serum uric acid concentrations are correlated with gout and clinical entities such as cardiovascular disease and diabetes. In the genome-wide association study KORA (Kooperative Gesundheitsforschung in der Region Augsburg) F3 500K (n = 1,644), the most significant SNPs associated with uric acid concentrations mapped within introns 4 and 6 of SLC2A9, a gene encoding a putative hexose transporter (effects: −0.23 to −0.36 mg/dl per copy of the minor allele). We replicated these findings in three independent samples from Germany (KORA S4 and SHIP (Study of Health in Pomerania)) and Austria (SAPHIR; Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk), with P values ranging from 1.2 × 10−8 to 1.0 × 10−32. Analysis of whole blood RNA expression profiles from a KORA F3 500K subgroup (n = 117) showed a significant association between the SLC2A9 isoform 2 and urate concentrations. The SLC2A9 genotypes also showed significant association with self-reported gout. The proportion of the variance of serum uric acid concentrations explained by genotypes was about 1.2% in men and 6% in women, and the percentage accounted for by expression levels was 3.5% in men and 15% in women.

Clear detection of ADIPOQ locus as the major gene for plasma adiponectin: Results of genome-wide association analyses including 4659 European individuals

OBJECTIVE Plasma adiponectin is strongly associated with various components of metabolic syndrome, type 2 diabetes and cardiovascular outcomes. Concentrations are highly heritable and differ between men and women. We therefore aimed to investigate the genetics of plasma adiponectin in men and women. METHODS We combined genome-wide association scans of three population-based studies including 4659 persons. For the replication stage in 13795 subjects, we selected the 20 top signals of the combined analysis, as well as the 10 top signals with p-values less than 1.0 x 10(-4) for each the men- and the women-specific analyses. We further selected 73 SNPs that were consistently associated with metabolic syndrome parameters in previous genome-wide association studies to check for their association with plasma adiponectin. RESULTS The ADIPOQ locus showed genome-wide significant p-values in the combined (p=4.3 x 10(-24)) as well as in both women- and men-specific analyses (p=8.7 x 10(-17) and p=2.5 x 10(-11), respectively). None of the other 39 top signal SNPs showed evidence for association in the replication analysis. None of 73 SNPs from metabolic syndrome loci exhibited association with plasma adiponectin (p>0.01). CONCLUSIONS We demonstrated the ADIPOQ gene as the only major gene for plasma adiponectin, which explains 6.7% of the phenotypic variance. We further found that neither this gene nor any of the metabolic syndrome loci explained the sex differences observed for plasma adiponectin. Larger studies are needed to identify more moderate genetic determinants of plasma adiponectin.

Association of eGFR-Related Loci Identified by GWAS with Incident CKD and ESRD

Family studies suggest a genetic component to the etiology of chronic kidney disease (CKD) and end stage renal disease (ESRD). Previously, we identified 16 loci for eGFR in genome-wide association studies, but the associations of these single nucleotide polymorphisms (SNPs) for incident CKD or ESRD are unknown. We thus investigated the association of these loci with incident CKD in 26,308 individuals of European ancestry free of CKD at baseline drawn from eight population-based cohorts followed for a median of 7.2 years (including 2,122 incident CKD cases defined as eGFR <60ml/min/1.73m2 at follow-up) and with ESRD in four case-control studies in subjects of European ancestry (3,775 cases, 4,577 controls). SNPs at 11 of the 16 loci (UMOD, PRKAG2, ANXA9, DAB2, SHROOM3, DACH1, STC1, SLC34A1, ALMS1/NAT8, UBE2Q2, and GCKR) were associated with incident CKD; p-values ranged from p = 4.1e-9 in UMOD to p = 0.03 in GCKR. After adjusting for baseline eGFR, six of these loci remained significantly associated with incident CKD (UMOD, PRKAG2, ANXA9, DAB2, DACH1, and STC1). SNPs in UMOD (OR = 0.92, p = 0.04) and GCKR (OR = 0.93, p = 0.03) were nominally associated with ESRD. In summary, the majority of eGFR-related loci are either associated or show a strong trend towards association with incident CKD, but have modest associations with ESRD in individuals of European descent. Additional work is required to characterize the association of genetic determinants of CKD and ESRD at different stages of disease progression.

Genetic-epidemiological evidence on genes associated with HDL cholesterol levels: A systematic in-depth review

High-density lipoprotein (HDL) particles exhibit multiple antiatherogenic effects. They are key players in the reverse cholesterol transport which shuttles cholesterol from peripheral cells (e.g. macrophages) to the liver or other tissues. This complex process is thought to represent the basis for the antiatherogenic properties of HDL particles. The amount of cholesterol transported in HDL particles is measured as HDL cholesterol (HDLC) and is inversely correlated with the risk for coronary artery disease: an increase of 1mg/dL of HDLC levels is associated with a 2% and 3% decrease of the risk for coronary artery disease in men and women, respectively. Genetically determined conditions with high HDLC levels (e.g. familial hyperalphalipoproteinemia) often coexist with longevity, and higher HDLC levels were found among healthy elderly individuals. HDLC levels are under considerable genetic control with heritability estimates of up to 80%. The identification and characterization of genetic variants associated with HDLC concentrations can provide new insights into the background of longevity. This review provides an extended overview on the current genetic-epidemiological evidence from association studies on genes involved in HDLC metabolism. It provides a path through the jungle of association studies which are sometimes confusing due to the varying and sometimes erroneous names of genetic variants, positions and directions of associations. Furthermore, it reviews the recent findings from genome-wide association studies which have identified new genes influencing HDLC levels. The yet identified genes together explain only a small amount of less than 10% of the HDLC variance, which leaves an enormous room for further yet to be identified genetic variants. This might be accomplished by large population-based genome-wide meta-analyses and by deep-sequencing approaches on the identified genes. The resulting findings will probably result in a re-drawing and extension of the involved metabolic pathways of HDLC metabolism.

Genome-Wide Association Analysis of High-Density Lipoprotein Cholesterol in the Population-Based KORA Study Sheds New Light on Intergenic Regions

Background—High-density lipoprotein cholesterol (HDLC) is a strong risk factor for atherosclerosis and is assumed to be under considerable genetic control. We aimed to identify gene regions that influence HDLC levels by a genome-wide association analysis in the population-based KORA (Cooperative Health Research in the Region of Augsburg) study. Methods and Results—In KORA S3/F3 (n=1643), we analyzed 377 865 quality-checked single-nucleotide polymorphisms (SNPs; 500K, Affymetrix, Santa Clara, Calif), complemented by the publicly available genome-wide association results from the Diabetes Genetics Initiative (n=2631) and by replication data from KORA S4 (n=4037) and the Copenhagen City Heart Study (n=9205). Among the 13 SNPs selected from the KORA S3/F3 500K probability value list, 3 showed consistent associations in subsequent replications: 1 SNP 10 kb upstream of CETP (pooled probability value=8.5×10−27), 1 SNP approximately 40 kb downstream of LIPG (probability value=4.67×10−10), both independent of previously reported SNPs, and 1 from an already reported region of LPL (probability value=2.82×10−11). Bioinformatical analyses indicate a potential functional relevance of the respective SNPs. Conclusions—The present genome-wide association study identified 2 interesting HDLC-relevant regions upstream of CETP and downstream of LIPG. This draws attention to the importance of long-range effects of intergenic regions, which have been underestimated so far, and may impact future candidate-gene–association studies toward extending the region analyzed. Furthermore, the present study reinforced CETP and LPL as HDLC genes and thereby underscores the power of this type of genome-wide association approach to pinpoint associations of common polymorphisms with effects explaining as little as 0.5% of the HDLC variance in the general population.

Sex-Specific Association of the Putative Fructose Transporter SLC2A9 Variants With Uric Acid Levels Is Modified by BMI

OBJECTIVE—High serum uric acid levels lead to gout and have been reported to be associated with an increased risk of hypertension, obesity, metabolic syndrome, type 2 diabetes, and cardiovascular disease. Recently, the putative fructose transporter SLC2A9 was reported to influence uric acid levels. The aim of the present study was to examine the association of four single nucleotide polymorphisms within this gene with uric acid levels and to determine whether this association is modified by obesity. RESEARCH DESIGN AND METHODS—Four single nucleotide polymorphisms within SLC2A9 (rs6855911, rs7442295, rs6449213, and rs12510549) were genotyped in the population-based prospective Bruneck Study (n = 800) and in a case-control study from Utah including 1,038 subjects recruited for severe obesity and 831 control subjects. RESULTS—We observed highly significant associations between all four polymorphisms and uric acid levels in all study groups. Each copy of the minor allele decreased age- and sex-adjusted uric acid levels by 0.30–0.35 mg/dl on average, which translates to a relative decrease of 5–6% with P values ranging from 10−9 to 10−11 in the combined analysis. An extended adjustment for BMI, creatinine, gout medication, and alcohol intake improved P values to a range of 10−14 to 10−20. The association was more pronounced in women and the population-based Bruneck Study and was significantly modified by BMI, with stronger effect sizes in individuals with high BMI. CONCLUSIONS—Genetic variants within SLC2A9 have significant effects on uric acid levels and are modified by sex and BMI.

Somatic Mutations throughout the Entire Mitochondrial Genome Are Associated with Elevated PSA Levels in Prostate Cancer Patients

The genetic etiology of prostate cancer, the most common form of male cancer in western countries, is complex and the interplay of disease genes with environmental factors is far from being understood. Studies on somatic mitochondrial DNA (mtDNA) mutations have become an important aspect of cancer research because these mutations might have functional consequences and/or might serve as biosensors for tumor detection and progression. We sequenced the entire mitochondrial genome (16,569 bp) from 30 prospectively collected pairs of macrodissected cancerous and benign cells from prostate cancer patients and compared their genetic variability. Given recent concerns regarding the authenticity of newly discovered mtDNA mutations, we implemented a high-quality procedure for mtDNA whole-genome sequencing. In addition, the mitochondrial genes MT-CO2, MT-CO3, MT-ATP6, and MT-ND6 were sequenced in further 35 paired samples from prostate cancer patients. We identified a total of 41 somatic mutations in 22 out of 30 patients: the majority of these mutations have not previously been observed in the human phylogeny. The presence of somatic mutations in transfer RNAs (tRNAs) was found to be associated with elevated PSA levels (14.25 ± 5.44 versus 7.15 ± 4.32 ng/ml; p = 0.004). The level and degree of heteroplasmy increased with increasing tumor activity. In summary, somatic mutations in the mitochondrial genome are frequent events in prostate cancer. Mutations mapping to mitochondrial tRNAs, ribosomal RNAs, and protein coding genes might impair processes that occur within the mitochondrial compartment (e.g., transcription, RNA processing, and translation) and might finally affect oxidative phosphorylation.

A common variant in the adiponutrin gene influences liver enzyme values

Background Two recent genome-wide association studies identified the liver expressed transmembrane protein adiponutrin to be associated with liver related phenotypes such as non-alcoholic fatty liver disease and liver function enzymes. These associations were not uniformly reported for various ethnicities. The aim of this study was to investigate a common non-synonymous variant within adiponutrin (rs738409, exon 3) with parameters of liver function in three independent West Eurasian study populations including a total of 4290 participants. Methods The study was performed in (1) the population based Bruneck Study (n=783), (2) the Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk Study from Austria based on a healthy working population (n=1705), and the Utah Obesity Case–Control Study including a group of 1019 severely obese individuals (average body mass index 46.0 kg/m2) and 783 controls from the same geographical region of Utah. Liver enzymes measured were alanine aminotransferase (ALT), aspartate aminotransferase (AST) and γ-glutamyl transferase (GGT). Results A strong recessive association of this polymorphism was found with age and gender adjusted ALT and AST concentrations: being homozygous for the minor allele resulted in a highly significant increase of ALT concentration of 3.53 U/l (p=1.86×10−9) and of AST concentration of 2.07 U/l (p=9.58×10−6), respectively. The associations were consistently found in all three study populations. Conclusion The highly significant associations of this transversion polymorphism within the adiponutrin gene with increased ALT and AST concentrations support a role for adiponutrin as a susceptibility gene for hepatic dysfunction.

Genetic evidence for a role of adiponutrin in the metabolism of apolipoprotein B-containing lipoproteins

Adiponutrin (PNPLA3) is a predominantly liver-expressed transmembrane protein with phospholipase activity that is regulated by fasting and feeding. Recent genome-wide association studies identified PNPLA3 to be associated with hepatic fat content and liver function, thus pointing to a possible involvement in the hepatic lipoprotein metabolism. The aim of this study was to examine the association between two common variants in the adiponutrin gene and parameters of lipoprotein metabolism in 23,274 participants from eight independent West-Eurasian study populations including six population-based studies [Bruneck (n = 800), KORA S3/F3 (n = 1644), KORA S4/F4 (n = 1814), CoLaus (n = 5435), SHIP (n = 4012), Rotterdam (n = 5967)], the SAPHIR Study as a healthy working population (n = 1738) and the Utah Obesity Case-Control Study including a group of 1037 severely obese individuals (average BMI 46 kg/m2) and 827 controls from the same geographical region of Utah. We observed a strong additive association of a common non-synonymous variant within adiponutrin (rs738409) with age-, gender-, and alanine-aminotransferase-adjusted lipoprotein concentrations: each copy of the minor allele decreased levels of total cholesterol on average by 2.43 mg/dl (P = 8.87 x 10(-7)), non-HDL cholesterol levels by 2.35 mg/dl (P = 2.27 x 10(-6)) and LDL cholesterol levels by 1.48 mg/dl (P = 7.99 x 10(-4)). These associations remained significant after correction for multiple testing. We did not observe clear evidence for associations with HDL cholesterol or triglyceride concentrations. In conclusion, our study suggests that adiponutrin is involved in the metabolism of apoB-containing lipoproteins.

INSIG2 polymorphism is neither associated with BMI nor with phenotypes of lipoprotein metabolism

Objective: A previous epidemiological study showed an association of the insulin‐induced gene 2 (INSIG2) gene with BMI. Additionally, experimental investigations in animals and cell culture provided evidence that this gene might be involved in lipoprotein and free fatty acid (FFA) metabolism. Therefore, the aim of this study was to examine the association between the rs7566605 variant near the INSIG2 gene and BMI and to extend it to other quantitative measures of obesity, as well as parameters of lipoprotein and FFA metabolism.