Meta-GWAS of PCSK9 levels detects two novel loci at APOB and TM6SF2.

BACKGROUND: Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key player in lipid metabolism, as it degrades low-density lipoprotein (LDL) receptors from hepatic cell membranes. So far, only variants of the PCSK9 gene locus were found to be associated with PCSK9 levels. Here we aimed to identify novel genetic loci that regulate PCSK9 levels and how they relate to other lipid traits. Additionally, we investigated to what extend the causal effect of PCSK9 on coronary artery disease (CAD) is mediated by low-density lipoprotein-cholesterol (LDL-C). METHODS AND RESULTS: We performed a genome-wide association study meta-analysis of PCSK9 levels in up to 12 721 samples of European ancestry. The estimated heritability was 10.3%, which increased to 12.6% using only samples from patients without statin treatment. We successfully replicated the known PCSK9 hit consisting of three independent signals. Interestingly, in a study of 300 African Americans, we confirmed the locus with a different PCSK9 variant. Beyond PCSK9, our meta-analysis detected three novel loci with genome-wide significance. Co-localization analysis with cis-eQTLs and lipid traits revealed biologically plausible candidate genes at two of them: APOB and TM6SF2. In a bivariate Mendelian Randomization analysis, we detected a strong effect of PCSK9 on LDL-C, but not vice versa. LDL-C mediated 63% of the total causal effect of PCSK9 on CAD. CONCLUSION: Our study identified novel genetic loci with plausible candidate genes affecting PCSK9 levels. Ethnic heterogeneity was observed at the PCSK9 locus itself. Although the causal effect of PCSK9 on CAD is mainly mediated by LDL-C, an independent direct effect also occurs.

Angiopoietin-like protein 8 differentially regulates ANGPTL3 and ANGPTL4 during postprandial partitioning of fatty acids.

Angiopoietin-like protein (ANGPTL)8 has been implicated in metabolic syndrome and reported to regulate adipose FA uptake through unknown mechanisms. Here, we studied how complex formation of ANGPTL8 with ANGPTL3 or ANGPTL4 varies with feeding to regulate LPL. In human serum, ANGPTL3/8 and ANGPTL4/8 complexes both increased postprandially, correlated negatively with HDL, and correlated positively with all other metabolic syndrome markers. ANGPTL3/8 also correlated positively with LDL-C and blocked LPL-facilitated hepatocyte VLDL-C uptake. LPL-inhibitory activity of ANGPTL3/8 was >100-fold more potent than that of ANGPTL3, and LPL-inhibitory activity of ANGPTL4/8 was >100-fold less potent than that of ANGPTL4. Quantitative analyses of inhibitory activities and competition experiments among the complexes suggested a model in which localized ANGPTL4/8 blocks the LPL-inhibitory activity of both circulating ANGPTL3/8 and localized ANGPTL4, allowing lipid sequestration into fat rather than muscle during the fed state. Supporting this model, insulin increased ANGPTL3/8 secretion from hepatocytes and ANGPTL4/8 secretion from adipocytes. These results suggest that low ANGPTL8 levels during fasting enable ANGPTL4-mediated LPL inhibition in fat tissue to minimize adipose FA uptake. During feeding, increased ANGPTL8 increases ANGPTL3 inhibition of LPL in muscle via circulating ANGPTL3/8, while decreasing ANGPTL4 inhibition of LPL in adipose tissue through localized ANGPTL4/8, thereby increasing FA uptake into adipose tissue. Excessive caloric intake may shift this system toward the latter conditions, possibly predisposing to metabolic syndrome.

PNPLA2 influences secretion of triglyceride-rich lipoproteins by human hepatoma cells.

Patatin-like phospholipase domain-containing proteins (PNPLAs) are involved in triglyceride hydrolysis and lipid-droplet homeostasis in mice, but the physiological significance of the PNPLAs for triglyceride metabolism in human hepatocytes is unclear. Here, we investigate the roles of PNPLA2, PNPLA3, and PNPLA4 in triglyceride metabolism of human Huh7 and HepG2 hepatoma cells using gene-specific inhibition methods. siRNA inhibition of PNPLA3 or PNPLA4 is not associated with changes in triglyceride hydrolysis, secretion of triglyceride-rich lipoproteins (TRLs), or triglyceride accumulation. However, PNPLA2 siRNA inhibition, both in the absence and presence of oleate-containing medium, or treatment with the PNPLA2 inhibitor Atglistatin reduced intracellular triglyceride hydrolysis and decreased TRL secretion. In contrast, PNPLA2 inhibition showed no effects on lipid-droplet homeostasis, which is the primary physiological function of PNPLA2 in nonhepatic tissues. Moreover, confocal microscopy analysis found no clear evidence for the localization of PNPLA2 around lipid droplets. However, significant colocalization of PNPLA2 with the endoplasmic reticulum marker protein disulfide-isomerase was found in HepG2 and Huh7 cells with Rcoloc values of 0.61 ± 0.06 and 0.81 ± 0.05, respectively. In conclusion, PNPLA2 influences TRL secretion, but is not involved in lipid-droplet homeostasis in human hepatoma cells, a physiological role that is quite distinct from the metabolic function of PNPLA2 in nonhepatic tissues.

Circulating Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Predicts Future Risk of Cardiovascular Events Independently of Established Risk Factors.

BACKGROUND: The secreted protein proprotein convertase subtilisin/kexin type 9 (PCSK9) is a promising new target for lowering plasma low-density lipoprotein cholesterol and preventing cardiovascular disease (CVD). The relationship between circulating PCSK9 and incident CVD in the general population is unknown. We investigated whether serum PCSK9 concentration is associated with incident CVD in a prospective cohort study of 4232 men and women 60 years of age at the time of recruitment. METHODS AND RESULTS: Incident CVD was recorded by matching to national registries. After 15 years of follow-up, a total of 491 incident events (fatal and nonfatal myocardial infarctions, unstable angina, deaths from coronary heart disease, fatal and nonfatal ischemic strokes) were recorded. Cox proportional hazards model was used to calculate hazard ratios with 95% confidence intervals. Baseline serum PCSK9 concentration predicted incident CVD; concentration in quartile 4 compared with quartile 1 was associated with a hazard ratio of 1.69 (95% confidence interval, 1.30-2.19) after adjustment for sex. Further adjustment for low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, lipoprotein(a), triglycerides, hypertension, diabetes mellitus, smoking, overweight, obesity, physical inactivity, and statin use resulted in a decrease in the hazard ratio to 1.48 (95% confidence interval, 1.12-1.95). CONCLUSIONS: Serum PCSK9 concentration is associated with future risk of CVD even after adjustments for established CVD risk factors. Further studies are needed to confirm this observation.

AllelicImbalance: an R/bioconductor package for detecting, managing, and visualizing allele expression imbalance data from RNA sequencing.

BACKGROUND: One aspect in which RNA sequencing is more valuable than microarray-based methods is the ability to examine the allelic imbalance of the expression of a gene. This process is often a complex task that entails quality control, alignment, and the counting of reads over heterozygous single-nucleotide polymorphisms. Allelic imbalance analysis is subject to technical biases, due to differences in the sequences of the measured alleles. Flexible bioinformatics tools are needed to ease the workflow while retaining as much RNA sequencing information as possible throughout the analysis to detect and address the possible biases. RESULTS: We present AllelicImblance, a software program that is designed to detect, manage, and visualize allelic imbalances comprehensively. The purpose of this software is to allow users to pose genetic questions in any RNA sequencing experiment quickly, enhancing the general utility of RNA sequencing. The visualization features can reveal notable, non-trivial allelic imbalance behavior over specific regions, such as exons. CONCLUSIONS: The software provides a complete framework to perform allelic imbalance analyses of aligned RNA sequencing data, from detection to visualization, within the robust and versatile management class, ASEset.

PLA2G10 Gene Variants, sPLA2 Activity, and Coronary Heart Disease Risk.

BACKGROUND: Observational studies report that secretory phospholipase A2 (sPLA2) activity is a marker for coronary heart disease (CHD) risk, and activity measures are thought to represent the composite activity of sPLA2-IIA, -V, and -X. The aim of this study was to use genetic variants of PLA2G10, encoding sPLA2-X, to investigate the contribution of sPLA2-X to the measure of sPLA2 activity and coronary heart disease (CHD) risk traits and outcome. METHODS AND RESULTS: Three PLA2G10 tagging single-nucleotide polymorphisms (rs72546339, rs72546340, and rs4003232) and a previously studied PLA2G10 coding single-nucleotide polymorphism rs4003228, R38C, were genotyped in a nested case: control cohort drawn from the prospective EPIC-Norfolk Study (2175 cases and 2175 controls). Meta-analysis of rs4003228 (R38C) and CHD was performed using data from the Northwick Park Heart Study II and 2 published cohorts AtheroGene and SIPLAC, providing in total an additional 1884 cases and 3119 controls. EPIC-Norfolk subjects in the highest tertile of sPLA2 activity were older and had higher inflammatory markers compared with those in the lowest tertile for sPLA2 activity. None of the PLA2G10 tagging single-nucleotide polymorphism nor R38C, a functional variant, were significantly associated with sPLA2 activity, intermediate CHD risk traits, or CHD risk. In meta-analysis, the summary odds ratio for R38C was odds ratio=0.97 (95% confidence interval, 0.77-1.22). CONCLUSIONS: PLA2G10 variants are not significantly associated with plasma sPLA2 activity or with CHD risk.

TM6SF2 is a regulator of liver fat metabolism influencing triglyceride secretion and hepatic lipid droplet content.

Genome-wide association studies have identified a locus on chromosome 19 associated with plasma triglyceride (TG) concentration and nonalcoholic fatty liver disease. However, the identity and functional role of the gene(s) responsible for these associations remain unknown. Of 19 expressed genes contained in this locus, none has previously been implicated in lipid metabolism. We performed gene expression studies and expression quantitative trait locus analysis in 206 human liver samples to identify the putative causal gene. Transmembrane 6 superfamily member 2 (TM6SF2), a gene with hitherto unknown function, expressed predominantly in liver and intestine, was identified as the putative causal gene. TM6SF2 encodes a protein of 351 amino acids with 7-10 predicted transmembrane domains. Otherwise, no other protein features were identified which could help to elucidate the function of TM6SF2. Protein subcellular localization studies with confocal microscopy demonstrated that TM6SF2 is localized in the endoplasmic reticulum and the ER-Golgi intermediate compartment of human liver cells. Functional studies for secretion of TG-rich lipoproteins (TRLs) and lipid droplet content were performed in human hepatoma Huh7 and HepG2 cells using confocal microscopy and siRNA inhibition and overexpression techniques. In agreement with the genome-wide association data, it was found that TM6SF2 siRNA inhibition was associated with reduced secretion of TRLs and increased cellular TG concentration and lipid droplet content, whereas TM6SF2 overexpression reduced liver cell steatosis. We conclude that TM6SF2 is a regulator of liver fat metabolism with opposing effects on the secretion of TRLs and hepatic lipid droplet content.

Novel genetic approach to investigate the role of plasma secretory phospholipase A2 (sPLA2)-V isoenzyme in coronary heart disease: modified Mendelian randomization analysis using PLA2G5 expression levels.

BACKGROUND: Secretory phospholipase A2 (sPLA2) enzymes are considered to play a role in atherosclerosis. sPLA2 activity encompasses several sPLA2 isoenzymes, including sPLA2-V. Although observational studies show a strong association between elevated sPLA2 activity and CHD, no assay to measure sPLA2-V levels exists, and the only evidence linking the sPLA2-V isoform to atherosclerosis progression comes from animal studies. In the absence of an assay that directly quantifies sPLA2-V levels, we used PLA2G5 mRNA levels in a novel, modified Mendelian randomization approach to investigate the hypothesized causal role of sPLA2-V in coronary heart disease (CHD) pathogenesis. METHODS AND RESULTS: Using data from the Advanced Study of Aortic Pathology, we identified the single-nucleotide polymorphism in PLA2G5 showing the strongest association with PLA2G5 mRNA expression levels as a proxy for sPLA2-V levels. We tested the association of this SNP with sPLA2 activity and CHD events in 4 prospective and 14 case-control studies with 27 230 events and 70 500 controls. rs525380C>A showed the strongest association with PLA2G5 mRNA expression (P=5.1×10(-6)). There was no association of rs525380C>A with plasma sPLA2 activity (difference in geometric mean of sPLA2 activity per rs525380 A-allele 0.4% (95% confidence intervals [-0.9%, 1.6%]; P=0.56). In meta-analyses, the odds ratio for CHD per A-allele was 1.02 (95% confidence intervals [0.99, 1.04]; P=0.20). CONCLUSIONS: This novel approach for single-nucleotide polymorphism selection for this modified Mendelian randomization analysis showed no association between rs525380 (the lead single-nucleotide polymorphism for PLA2G5 expression, a surrogate for sPLA2-V levels) and CHD events. The evidence does not support a causal role for sPLA2-V in CHD.

Secretory phospholipase A(2)-IIA and cardiovascular disease: a mendelian randomization study.

OBJECTIVES: This study sought to investigate the role of secretory phospholipase A2 (sPLA2)-IIA in cardiovascular disease. BACKGROUND: Higher circulating levels of sPLA2-IIA mass or sPLA2 enzyme activity have been associated with increased risk of cardiovascular events. However, it is not clear if this association is causal. A recent phase III clinical trial of an sPLA2 inhibitor (varespladib) was stopped prematurely for lack of efficacy. METHODS: We conducted a Mendelian randomization meta-analysis of 19 general population studies (8,021 incident, 7,513 prevalent major vascular events [MVE] in 74,683 individuals) and 10 acute coronary syndrome (ACS) cohorts (2,520 recurrent MVE in 18,355 individuals) using rs11573156, a variant in PLA2G2A encoding the sPLA2-IIA isoenzyme, as an instrumental variable. RESULTS: PLA2G2A rs11573156 C allele associated with lower circulating sPLA2-IIA mass (38% to 44%) and sPLA2 enzyme activity (3% to 23%) per C allele. The odds ratio (OR) for MVE per rs11573156 C allele was 1.02 (95% confidence interval [CI]: 0.98 to 1.06) in general populations and 0.96 (95% CI: 0.90 to 1.03) in ACS cohorts. In the general population studies, the OR derived from the genetic instrumental variable analysis for MVE for a 1-log unit lower sPLA2-IIA mass was 1.04 (95% CI: 0.96 to 1.13), and differed from the non-genetic observational estimate (OR: 0.69; 95% CI: 0.61 to 0.79). In the ACS cohorts, both the genetic instrumental variable and observational ORs showed a null association with MVE. Instrumental variable analysis failed to show associations between sPLA2 enzyme activity and MVE. CONCLUSIONS: Reducing sPLA2-IIA mass is unlikely to be a useful therapeutic goal for preventing cardiovascular events.

Identification of a functional apolipoprotein E promoter polymorphism regulating plasma apolipoprotein E concentration.

OBJECTIVE: There is compelling evidence that the plasma apolipoprotein E (APOE) concentration, in addition to the APOE ε2/ε3/ε4 genotype, influences plasma lipoprotein levels, but the functional genetic variants influencing the plasma APOE concentration have not been identified. APPROACH AND RESULTS: Genome-wide association studies in 2 cohorts of healthy, middle-aged subjects identified the APOE locus as the only genetic locus showing robust associations with the plasma APOE concentration. Fine-mapping of the APOE locus confirmed that the rs7412 ε2-allele is the primary genetic variant responsible for the relationship with plasma APOE concentration. Further mapping of the APOE locus uncovered that rs769446 (-427T/C) in the APOE promoter is independently associated with the plasma APOE concentration. Expression studies in 199 human liver samples demonstrated that the rs769446 C-allele is associated with increased APOE mRNA levels (P=0.015). Transient transfection studies and electrophoretic mobility shift assays in human hepatoma HepG2 cells corroborated the role of rs769446 in transcriptional regulation of APOE. However, no relationships were found between rs769446 genotype and plasma lipoprotein levels in 2 cohorts (n=1648 and n=1039) of healthy middle-aged carriers of the APOE ε3/ε3 genotype. CONCLUSIONS: rs769446 is a functional polymorphism involved in the regulation of the plasma APOE concentration.

Common and low-frequency genetic variants in the PCSK9 locus influence circulating PCSK9 levels.

OBJECTIVE: Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a circulating protein that influences plasma low-density lipoprotein concentration and susceptibility to coronary heart disease. Circulating PCSK9 levels show considerable interindividual differences, but the factors responsible for this variation are largely unknown. METHODS AND RESULTS: We analyzed circulating PCSK9 levels in 4 cohorts of healthy, middle-aged Swedes (n=5722) and found that PCSK9 levels varied over ≈50-fold range, showed a positive relationship with plasma low-density lipoprotein-cholesterol concentration, and were associated with plasma triglyceride, fibrinogen, insulin, and glucose concentrations. A genome-wide association study conducted in 2 cohorts (n=1215) failed to uncover common genetic variants robustly associated with variation in circulating PCSK9 level. As expected, the minor allele of the PCSK9 R46L variant was in all cohorts associated with reduced PCSK9 levels and decreased plasma low-density lipoprotein-cholesterol concentrations, but no relationship was observed with the plasma triglyceride concentration. Further mapping of the PCSK9 locus revealed a common polymorphism (rs2479415, minor allele frequency 43.9%), located ≈6 kb upstream from PCSK9, which is independently associated with increased circulating PCSK9 levels. CONCLUSIONS: Common and low-frequency genetic variants in the PCSK9 locus influence the pronounced interindividual variation in circulating PCSK9 levels in healthy, middle-aged white (predominantly Swedish) subjects.

Genome wide association study identifies KCNMA1 contributing to human obesity.

BACKGROUND: Recent genome-wide association (GWA) analyses have identified common single nucleotide polymorphisms (SNPs) that are associated with obesity. However, the reported genetic variation in obesity explains only a minor fraction of the total genetic variation expected to be present in the population. Thus many genetic variants controlling obesity remain to be identified. The aim of this study was to use GWA followed by multiple stepwise validations to identify additional genes associated with obesity. METHODS: We performed a GWA analysis in 164 morbidly obese subjects (BMI:body mass index>40 kg/m2) and 163 Swedish subjects (>45 years) who had always been lean. The 700 SNPs displaying the strongest association with obesity in the GWA were analyzed in a second cohort comprising 460 morbidly obese subjects and 247 consistently lean Swedish adults. 23 SNPs remained significantly associated with obesity (nominal P<0.05) and were in a step-wise manner followed up in five additional cohorts from Sweden, France, and Germany together comprising 4214 obese and 5417 lean or population-based control individuals. Three samples, n=4133, were used to investigate the population-based associations with BMI. Gene expression in abdominal subcutaneous adipose tissue in relation to obesity was investigated for14 adults. RESULTS: Potassium channel, calcium activated, large conductance, subfamily M, alpha member (KCNMA1) rs2116830*G and BDNF rs988712*G were associated with obesity in five of six investigated case-control cohorts. In meta-analysis of 4838 obese and 5827 control subjects we obtained genome-wide significant allelic association with obesity for KCNMA1 rs2116830*G with P=2.82×10(-10) and an odds ratio (OR) based on cases vs controls of 1.26 [95% C.I. 1.12-1.41] and for BDNF rs988712*G with P=5.2×10(-17) and an OR of 1.36 [95% C.I. 1.20-1.55]. KCNMA1 rs2116830*G was not associated with BMI in the population-based samples. Adipose tissue (P=0.0001) and fat cell (P=0.04) expression of KCNMA1 was increased in obesity. CONCLUSIONS: We have identified KCNMA1 as a new susceptibility locus for obesity, and confirmed the association of the BDNF locus at the genome-wide significant level.

Association of genetic risk variants with expression of proximal genes identifies novel susceptibility genes for cardiovascular disease.

BACKGROUND: Population-based genome-wide association studies have identified several single nucleotide polymorphisms (SNPs) associated with cardiovascular disease or its risk factors. Genes in close proximity to these risk-SNPs are often thought to be pathogenetically important based on their location alone. However, the actual connections between SNPs and disease mechanisms remain largely unknown. METHODS AND RESULTS: To identify novel susceptibility genes, we investigated how 166 SNPs previously found to be associated with increased cardiovascular risk and/or predisposing metabolic traits relate to the expression of nearby genes. Gene expression in 577 samples of aorta, liver, mammary artery, and carotid atherosclerotic plaque was measured using expression arrays. For 47 SNPs, the expression levels of proximal genes (located within 200 kb) were affected (P<0.005). More than 20 of these genes had not previously been identified as candidate genes for cardiovascular or related metabolic traits. SNP-associated gene effects were tissue-specific and the tissue specificity was phenotype-dependent. CONCLUSIONS: This study demonstrates several instances of association between risk-SNPs and genes immediately adjacent to them. It also demonstrates instances in which the associated gene is not the immediately proximal and obvious candidate gene for disease. This shows the necessity of careful studies of genetic marker data as a first step toward application of genome-wide association studies findings in a clinical setting.

DGAT1 participates in the effect of HNF4A on hepatic secretion of triglyceride-rich lipoproteins.

OBJECTIVE: Hepatocyte nuclear factor-4alpha (HNF4A) is a transcription factor that influences plasma triglyceride metabolism via an as of yet unknown mechanism. In this study, we searched for the critical protein that mediates this effect using different human model systems. METHODS AND RESULTS: Up- and downregulation of HNF4A in human hepatoma Huh7 and HepG2 cells was associated with marked changes in the secretion of triglyceride-rich lipoproteins (TRLs). Short interfering RNA (siRNA) inhibition of HNF4A influenced the expression of several genes, including acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1). siRNA knockdown of DGAT1 reduced DGAT1 activity and decreased the secretion of TRLs. No additive effects of combined siRNA inhibition of HNF4A and DGAT1 were found on the secretion of TRLs, whereas the increase in TRL secretion induced by HNF4A overexpression was largely abolished by DGAT1 siRNA inhibition. A putative binding site for HNF4A was defined by in silico and in vitro methods. HNF4A and DGAT1 expressions were analyzed in 80 human liver samples, and significant relationships were observed between HNF4A and DGAT1 mRNA levels (r(2)=0.50, P<0.0001) and between DGAT1 mRNA levels and plasma triglyceride concentration (r(2)=0.09, P<0.01). CONCLUSION: This study identified DGAT1 as an important protein that participates in the effect of HNF4A on hepatic secretion of TRLs.

Insulin-induced gene 2 involvement in human adipocyte metabolism and body weight regulation.

BACKGROUND: Insulin-induced genes (INSIGs) encode proteins that block proteolytic activation of sterol regulatory element-binding proteins, transcription factors that regulate lipogenic enzymes, and adipocyte differentiation. OBJECTIVE: Here, we analyzed the relative significance of INSIG1 and INSIG2 in human liver and adipocyte metabolism, and defined a novel, functional polymorphism in the promoter of INSIG2 associated with body mass index. RESEARCH METHODS: Variations in gene expression of different human tissues, of hepatoma cells exposed to INSIG1 and INSIG2 gene silencing probes, and of differentiating 3T3-L1 adipocytes were determined by real-time quantitative PCR. The functional significance of a novel polymorphism in the promoter of INSIG2 was analyzed using in vitro methods and gene expression analysis of human adipose tissue, whereas the phenotype associated with this polymorphism was studied in two cohorts of middle-aged men. RESULTS: Gene expression analysis of 17 human tissues demonstrated that INSIG1 is highly expressed in the liver, whereas INSIG2 is ubiquitously expressed. Gene silencing experiments confirmed that INSIG1, but not INSIG2, regulates the expression of sterol regulatory element-binding proteins target genes in human hepatoma cells. In contrast, adipocyte differentiation of 3T3-L1 cells was associated with a 13-fold increase in expression of INSIG2. Significant relationships between the INSIG2-102G/A polymorphism and body mass index were observed in two cohorts of middle-aged men (ANOVA P = 0.017 and 0.044, respectively). In vitro studies and analysis of allele-specific expression in human adipose tissue substantiated the functional significance of the INSIG2-102G/A polymorphism. CONCLUSION: INSIG2 is involved in adipocyte metabolism and body weight regulation.

Common polymorphisms in the CYP7A1 gene do not contribute to variation in rates of bile acid synthesis and plasma LDL cholesterol concentration.

Transcriptional regulation of the cholesterol 7alpha-hydroxylase (CYP7AI) gene is of critical importance for bile acid and cholesterol metabolism. We evaluated the physiological significance of two common polymorphisms (-203C/A and -469T/C) in the promoter region of the CYP7AI gene. No evidence was found for physiological differences between either the -203C and -203A alleles or the -469T and -469C alleles in transient transfection studies using native 834bp promoter constructs. Moreover, no association was observed between the CYP7AI promoter polymorphisms and the hepatic cholesterol 7alpha-hydroxylase activity and parameters of bile acid synthesis rates, as analyzed in subjects with gallstone disease. In addition, no relationships were found between the promoter polymorphisms and plasma LDL cholesterol concentration in association studies conducted in three different groups of middle-aged Swedish men. Finally, near complete allelic association was found between the two promoter polymorphisms and the IVS6+363G/A polymorphism at the 3' end of the CYP7AI gene (|D'|=0.98), indicating strong linkage disequilibrium across the whole CYP7AI gene. It is concluded that common polymorphisms of the CYP7A1 gene do not contribute to variation in cholesterol 7alpha-hydroxylase activity, rates of bile acid synthesis and plasma LDL cholesterol concentration in humans.

Mutation in the sterol 27-hydroxylase gene associated with fatal cholestasis in infancy.

BACKGROUND: Inborn errors of bile acid synthesis are rare but potentially treatable causes of neonatal cholestasis. We here present a cholestatic infant with an ongoing cytomegalovirus infection who despite intensive treatment died of severe liver disease at 4 months of age. METHODS: The urinary steroids were investigated by electrospray mass spectrometry and gas chromatography mass spectrometry. Oxysterols in plasma were analysed by isotope dilution mass spectrometry. Mutations in the sterol 27-hydroxylase gene were detected by PCR. RESULTS: Glucuronidated bile alcohols, which are known to be excreted by patients with cerebrotendinous xanthomatosis (CTX) were detected in the urine. Analysis of plasma revealed markedly reduced levels of 27-hydroxycholesterol. Mutation analysis showed the presence of a stop codon in exon 7, confirming the diagnosis of CTX, a rare disease not previously diagnosed in Sweden. CONCLUSIONS: Fetal and neonatal deaths among siblings of patients with CTX have been reported previously and the present case supports the contention that reduced activity of the sterol 27-hydroxylase may predispose to the development of neonatal cholestasis. The associated viral infection may have further precipitated the liver disease. Since CTX, like other inborn errors of bile acid synthesis may be treated with bile acids an early diagnosis is essential. Thus, the analysis of urine by electrospray mass spectrometry is highly recommended in the investigation of patients with neonatal cholestasis.