Statin-induced expression change of INSIG1 in lymphoblastoid cell lines correlates with plasma triglyceride statin response in a sex-specific manner.

Statins are widely prescribed to lower plasma low-density lipoprotein (LDL) cholesterol levels. They also modestly reduce plasma triglyceride (TG), an independent cardiovascular disease risk factor, in most people. The mechanism and inter-individual variability of TG statin response is poorly understood. We measured statin-induced gene expression changes in lymphoblastoid cell lines derived from 150 participants of a simvastatin clinical trial and identified 23 genes (false discovery rate, FDR=15%) with expression changes correlated with plasma TG response. The correlation of insulin-induced gene 1 (INSIG1) expression changes with TG response (rho=0.32, q=0.11) was driven by men (interaction P=0.0055). rs73161338 was associated with INSIG1 expression changes (P=5.4 × 10-5) and TG response in two statin clinical trials (P=0.0048), predominantly in men. A combined model including INSIG1 expression level and splicing changes accounted for 29.5% of plasma TG statin response variance in men (P=5.6 × 10-6). Our results suggest that INSIG1 variation may contribute to statin-induced changes in plasma TG in a sex-specific manner.

Transcriptomic variation of pharmacogenes in multiple human tissues and lymphoblastoid cell lines.

Variation in the expression level and activity of genes involved in drug disposition and action ('pharmacogenes') can affect drug response and toxicity, especially when in tissues of pharmacological importance. Previous studies have relied primarily on microarrays to understand gene expression differences, or have focused on a single tissue or small number of samples. The goal of this study was to use RNA-sequencing (RNA-seq) to determine the expression levels and alternative splicing of 389 Pharmacogenomics Research Network pharmacogenes across four tissues (liver, kidney, heart and adipose) and lymphoblastoid cell lines, which are used widely in pharmacogenomics studies. Analysis of RNA-seq data from 139 different individuals across the 5 tissues (20-45 individuals per tissue type) revealed substantial variation in both expression levels and splicing across samples and tissue types. Comparison with GTEx data yielded a consistent picture. This in-depth exploration also revealed 183 splicing events in pharmacogenes that were previously not annotated. Overall, this study serves as a rich resource for the research community to inform biomarker and drug discovery and use.

Disrupted nitric oxide signaling due to GUCY1A3 mutations increases risk for moyamoya disease, achalasia and hypertension.

Moyamoya disease (MMD) is a progressive vasculopathy characterized by occlusion of the terminal portion of the internal carotid arteries and its branches, and the formation of compensatory moyamoya collateral vessels. Homozygous mutations in GUCY1A3 have been reported as a cause of MMD and achalasia. Probands (n = 96) from unrelated families underwent sequencing of GUCY1A3. Functional studies were performed to confirm the pathogenicity of identified GUCY1A3 variants. Two affected individuals from the unrelated families were found to have compound heterozygous mutations in GUCY1A3. MM041 was diagnosed with achalasia at 4 years of age, hypertension and MMD at 18 years of age. MM149 was diagnosed with MMD and hypertension at the age of 20 months. Both individuals carry one allele that is predicted to lead to haploinsufficiency and a second allele that is predicted to produce a mutated protein. Biochemical studies of one of these alleles, GUCY1A3 Cys517Tyr, showed that the mutant protein (a subunit of soluble guanylate cyclase) has a significantly blunted signaling response with exposure to nitric oxide (NO). GUCY1A3 missense and haploinsufficiency mutations disrupt NO signaling leading to MMD and hypertension, with or without achalasia.

Pathogenic FBN1 variants in familial thoracic aortic aneurysms and dissections.

Marfan syndrome (MFS) due to mutations in FBN1 is a known cause of thoracic aortic aneurysms and acute aortic dissections (TAAD) associated with pleiotropic manifestations. Genetic predisposition to TAAD can also be inherited in families in the absence of syndromic features, termed familial TAAD (FTAAD), and several causative genes have been identified to date. FBN1 mutations can also be identified in FTAAD families, but the frequency of these mutations has not been established. We performed exome sequencing of 183 FTAAD families and identified pathogenic FBN1 variants in five (2.7%) of these families. We also identified eight additional FBN1 rare variants that could not be unequivocally classified as disease-causing in six families. FBN1 sequencing should be considered in individuals with FTAAD even without significant systemic features of MFS.

Variation in the TLR10/TLR1/TLR6 locus is the major genetic determinant of interindividual difference in TLR1/2-mediated responses.

Toll-like receptor (TLR)-mediated innate immune responses are important in early host defense. Using a candidate gene approach, we previously identified genetic variation within TLR1 that is associated with hyper-responsiveness to a TLR1/2 agonist in vitro and with death and organ dysfunction in patients with sepsis. Here we report a genome-wide association study (GWAS) designed to identify genetic loci controlling whole blood cytokine responses to the TLR1/2 lipopeptide agonist, Pam(3)CSK(4) (N-palmitoyl-S-dipalmitoylglyceryl Cys-Ser-(Lys)(4)) ex vivo. We identified a very strong association (P<1 × 10(-27)) between genetic variation within the TLR10/1/6 locus on chromosome 4, and Pam(3)CSK(4)-induced cytokine responses. This was the predominant association explaining over 35% of the population variance for this phenotype. Notably, strong associations were observed within TLR10, suggesting that genetic variation in TLR10 may influence bacterial lipoprotein-induced responses. These findings establish the TLR10/1/6 locus as the dominant common genetic factor controlling interindividual variability in Pam(3)CSK(4)-induced whole blood responses in the healthy population.

Novel rare variants in congenital cardiac arrhythmia genes are frequent in drug-induced torsades de pointes.

Marked prolongation of the QT interval and polymorphic ventricular tachycardia following medication (drug-induced long QT syndrome, diLQTS) is a severe adverse drug reaction (ADR) that phenocopies congenital long QT syndrome (cLQTS) and is one of the leading causes for drug withdrawal and relabeling. We evaluated the frequency of rare non-synonymous variants in genes contributing to the maintenance of heart rhythm in cases of diLQTS using targeted capture coupled to next-generation sequencing. Eleven of 31 diLQTS subjects (36%) carried a novel missense mutation in genes with known congenital arrhythmia associations or with a known cLQTS mutation. In the 26 Caucasian subjects, 23% carried a highly conserved rare variant predicted to be deleterious to protein function in these genes compared with only 2-4% in public databases (P<0.003). We conclude that the rare variation in genes responsible for congenital arrhythmia syndromes is frequent in diLQTS. Our findings demonstrate that diLQTS is a pharmacogenomic syndrome predisposed by rare genetic variants.

Sequence variation in the human angiotensin converting enzyme.

Angiotensin converting enzyme (encoded by the gene DCP1, also known as ACE) catalyses the conversion of angiotensin I to the physiologically active peptide angiotensin II, which controls fluid-electrolyte balance and systemic blood pressure. Because of its key function in the renin-angiotensin system, many association studies have been performed with DCP1. Nearly all studies have associated the presence (insertion, I) or absence (deletion, D) of a 287-bp Alu repeat element in intron 16 with the levels of circulating enzyme or cardiovascular pathophysiologies. Many epidemiological studies suggest that the DCP1*D allele confers increased susceptibility to cardiovascular disease; however, other reports have found no such association or even a beneficial effect. We present here the complete genomic sequence of DCP1 from 11 individuals, representing the longest contiguous scan (24 kb) for sequence variation in human DNA. We identified 78 varying sites in 22 chromosomes that resolved into 13 distinct haplotypes. Of the variant sites, 17 were in absolute linkage disequilibrium with the commonly typed Alu insertion/deletion polymorphism, producing two distinct and distantly related clades. We also identified a major subdivision in the Alu deletion clade that enables further analysis of the traits associated with this gene. The diversity uncovered in DCP1 is comparable to that described for other regions in the human genome. The highly correlated structure in DCP1 raises important issues for the determination of functional DNA variants within genes and genetic studies in humans based on marker association.

DNA sequence diversity in a 9.7-kb region of the human lipoprotein lipase gene.

Lipoprotein lipase plays a central role in lipid metabolism and the gene that encodes this enzyme (LPL) is a candidate susceptibility gene for cardiovascular disease. Here we report the complete sequence of a fraction of the LPL gene for 71 individuals (142 chromosomes) from three populations that may have different histories affecting the organization of the sequence variation. Eighty-eight sites in this 9.7 kb vary among individuals from these three populations. Of these, 79 were single nucleotide substitutions and 9 sites involved insertion-deletion variations. The average nucleotide diversity across the region was 0.2% (or on average 1 variable site every 500 bp). At 34 of these sites, the variation was found in only one of the populations, reflecting the differing population and mutational histories. If LPL is a typical human gene, the pattern of sequence variation that exists in introns as well as exons, even for the small number of samples considered here, will present challenges for the identification of sites, or combinations of sites, that influence variation in risk of disease in the population at large.

Identification and physical mapping of a polymorphic human T cell receptor V beta gene with a frequent null allele.

Germline variation in genes that encode the human T cell receptors (TCRs) may have an important influence in shaping the immune T cell repertoire. In this report we describe a frequent null allele of the human V beta 18 gene, resulting from a nucleotide substitution that creates a stop codon (CGA<-->TGA). Approximately 11% of the population tested was homozygous for this null allele, indicating that this is a frequent "hole in the repertoire." We confirmed that there is a greatly reduced (undetectable) level of V beta 18 mRNA in peripheral blood lymphocytes from an individual homozygous for this null allele. In addition, all heterozygous individuals expressed detectable levels of only the functional V beta 18 allele in their peripheral blood lymphocytes. Two other DNA polymorphisms were identified in V beta 18, one of which would result in an amino acid substitution in an expressed V beta 18 gene. Genotypes for all three of these V beta 18 DNA polymorphisms were determined in a group of unrelated individuals. Statistical analyses of the associations between alleles of the V beta 18 polymorphisms and those of other DNA polymorphisms in the TCR beta locus suggested a close physical proximity between the V beta 18 gene and the 3' end of the C beta 2 region. This localization of human V beta 18 had been previously predicted by the sequence homology between human V beta 18 and mouse V beta 14, a V gene segment previously mapped to 3' of the mouse C beta genes. We confirmed this localization of the human V beta 18 gene by isolating a cosmid clone that contains both the V beta 18 and C beta 2 segments. Mapping by restriction enzyme digestion and by the polymerase chain reaction indicated that the V beta 18 gene segment is approximately 9 kb 3' of the C beta 2 gene, making this the only known human V beta gene 3' of the C beta region.

Comparison of exon 5 sequences from 35 class I genes of the BALB/c mouse.

DNA sequences of the fifth exon, which encodes the transmembrane domain, were determined for the BALB/c mouse class I MHC genes and used to study the relationships between them. Based on nucleotide sequence similarity, the exon 5 sequences can be divided into seven groups. Although most members within each group are at least 80% similar to each other, comparison between groups reveals that the groups share little similarity. However, in spite of the extensive variation of the fifth exon sequences, analysis of their predicted amino acid translations reveals that only four class I gene fifth exons have frameshifts or stop codons that terminate their translation and prevent them from encoding a domain that is both hydrophobic and long enough to span a lipid bilayer. Exactly 27 of the remaining fifth exons could encode a domain that is similar to those of the transplantation antigens in that it consists of a proline-rich connecting peptide, a transmembrane segment, and a cytoplasmic portion with membrane-anchoring basic residues. The conservation of this motif in the majority of the fifth exon translations in spite of extensive variation suggests that selective pressure exists for these exons to maintain their ability to encode a functional transmembrane domain, raising the possibility that many of the nonclassical class I genes encode functionally important products.

An excess of rare genetic variation in ABCE1 among Yorubans and African-American individuals with HIV-1.

Signatures of natural selection occur throughout the human genome and can be detected at the sequence level. We have re-sequenced ABCE1, a host candidate gene essential for HIV-1 capsid assembly, in European- (n=23) and African-descent (Yoruban; n=24) reference populations for genetic variation discovery. We identified an excess of rare genetic variation in Yoruban samples, and the resulting Tajima's D was low (-2.27). The trend of excess rare variation persisted in flanking candidate genes ANAPC10 and OTUD4, suggesting that this pattern of positive selection can be detected across the 184.5 kb examined on chromosome 4. Owing to ABCE1's role in HIV-1 replication, we re-sequenced the candidate gene in three small cohorts of HIV-1-infected or resistant individuals. We were able to confirm the excess of rare genetic variation among HIV-1-positive African-American individuals (n=53; Tajima's D=-2.34). These results highlight the potential importance of ABCE1's role in infectious diseases such as HIV-1.

The Human Genome Project: creating an infrastructure for biology and medicine.

The Human Genome Project (HGP) is an international effort to map and sequence the human genome. It combines skills from diverse fields of biological and technological research, thus establishing deeper interactions between scientific disciplines. The combination of these skills should stimulate many advances in both pure and applied fields of research and give rise to new, interdisciplinary training programs. Some critics say that the HGP will damage biomedical research; however, we argue that it will bring new funds to the field and create a large ripple effect by providing new research opportunities through its discoveries.

Coagulation factor VII gene haplotypes, obesity-related traits, and cardiovascular risk in young women.

BACKGROUND: Associations between common F7 haplotypes, plasma factor VII (FVII) levels, and cardiovascular risk have recently been reported in population studies involving predominantly European men. METHODS: We assessed associations between F7 haplotypes and cardiovascular risk in two US population-based studies: a case-control study of these alleles related to a decreased risk of arterial thrombotic outcomes such as myocardial infarction (MI) in young-to-middle-aged women (n = 671), and a cohort study of cardiovascular disease risk factors in young women (n = 1040). RESULTS: The high-expression F7 haplotype B (containing the promoter variant allele -402A) was associated with an increased FVII level among controls, but not with MI risk. Women carrying a> or =1 copy of the low FVII expression level haplotype C (containing the -401T/-323del/-122C and Gln353 alleles) had decreased FVII levels and decreased risk of MI (odds ratio 0.54, 95% CI 0.31-0.93) compared with women homozygous for the most common haplotype A. Haplotype C was also associated with a decreased body mass index (BMI) and an increased high-density lipoprotein (HDL) cholesterol level, but not with MI risk after adjustment for these metabolic risk factors. In a cohort study composed of young US women, individuals homozygous for haplotype C had a lower BMI and lower systolic blood pressure, but the association between the F7 haplotype and HDL cholesterol was not confirmed. CONCLUSION: Common FVII haplotypes may contribute to the risk of MI in women, but the mechanisms appear complex. The association between F7 haplotypes and MI susceptibility may be mediated in part through an influence on atherogenic risk factors such as BMI.

Association between patterns of nucleotide variation across the three fibrinogen genes and plasma fibrinogen levels: the Coronary Artery Risk Development in Young Adults (CARDIA) study.

BACKGROUND: Previous genotype-phenotype association studies of fibrinogen have been limited by incomplete knowledge of genomic sequence variation within and between major ethnic groups in FGB, FGA, and FGG. METHODS: We characterized the linkage disequilibrium patterns and haplotype structure across the human fibrinogen gene locus in European- and African-American populations. We analyzed the association between common polymorphisms in the fibrinogen genes and circulating levels of both 'functional' fibrinogen (measured by the Clauss clotting rate method) and total fibrinogen (measured by immunonephelometry) in a large, multi-center, bi-racial cohort of young US adults. RESULTS: A common haplotype tagged by the A minor allele of the well-studied FGB-455 G/A promoter polymorphism (FGB 1437) was confirmed to be strongly associated with increased plasma fibrinogen levels. Two non-coding variants specific to African-American chromosomes, FGA 3845 A and FGG 5729 G, were each associated with lower plasma fibrinogen levels. In European-Americans, a common haplotype tagged by FGA Thr312Ala and several other variant alleles across the fibrinogen gene locus was strongly associated with decreased fibrinogen levels as measured by functional assay, but not by immunoassay. Overall, common polymorphisms within the three fibrinogen genes explain < 2% of the variability in plasma fibrinogen concentration. CONCLUSIONS: In young adults, fibrinogen multi-locus genotypes are associated with plasma fibrinogen levels. The specific single nucleotide polymorphism and haplotype patterns for these associations differ according to population and also according to phenotypic assay. It is likely that a substantial proportion of the heritable component of plasma fibrinogen concentration is due to genetic variation outside the three fibrinogen genes.

Pharmacogenetic allele nomenclature: International workgroup recommendations for test result reporting.

This article provides nomenclature recommendations developed by an international workgroup to increase transparency and standardization of pharmacogenetic (PGx) result reporting. Presently, sequence variants identified by PGx tests are described using different nomenclature systems. In addition, PGx analysis may detect different sets of variants for each gene, which can affect interpretation of results. This practice has caused confusion and may thereby impede the adoption of clinical PGx testing. Standardization is critical to move PGx forward.

SNPing in the human genome.

More than a million genetic markers in the form of single nucleotide polymorphisms are now available for use in genotype-phenotype studies in humans. The application of new strategies for representational cloning and sequencing from genomes combined with the mining of high-quality sequence variations in clone overlaps of genomic and/or cDNA sequences has played an important role in generating this new resource. The focus of variation analysis is now shifting from the identification of new markers to their typing in populations, and novel typing strategies are rapidly emerging. Assay readouts on oligonucleotide arrays, in microtiter plates, gels, flow cytometers and mass spectrometers have all been developed, but decreasing cost and increasing throughput of DNA typing remain key if high-density genetic maps are to be applied on a large scale.

Cladistic structure within the human Lipoprotein lipase gene and its implications for phenotypic association studies.

Haplotype variation in 9.7 kb of genomic DNA sequence from the human lipoprotein lipase (LPL) gene was scored in three populations: African-Americans from Jackson, Mississippi (24 individuals), Finns from North Karelia, Finland (24), and non-Hispanic whites from Rochester, Minnesota (23). Earlier analyses had indicated that recombination was common but concentrated into a hotspot and that recurrent mutations at multiple sites may have occurred. We show that much evolutionary structure exists in the haplotype variation on either side of the recombinational hotspot. By peeling off significant recombination events from a tree estimated under the null hypothesis of no recombination, we also reveal some cladistic structure not disrupted by recombination during the time to coalescence of this variation. Additional cladistic structure is estimated to have emerged after recombination. Many apparent multiple mutational events at sites still remain after removing the effects of the detected recombination/gene conversion events. These apparent multiple events are found primarily at sites identified as highly mutable by previous studies, strengthening the conclusion that they are true multiple events. This analysis portrays the complexity of the interplay among many recombinational and mutational events that would be needed to explain the patterns of haplotype diversity in this gene. The cladistic structure in this region is used to identify four to six single-nucleotide polymorphisms (SNPs) that would provide disequilibrium coverage over much of this region. These sites may be useful in identifying phenotypic associations with variable sites in this gene. Evolutionary considerations also imply that the SNPs in the 3' region should have general utility in most human populations, but the 5' SNPs may be more population specific. Choosing SNPs at random would generally not provide adequate disequilibrium coverage of the sequenced region.