The QT interval, an electrocardiographic measure reflecting myocardial repolarization, is a heritable trait. QT prolongation is a risk factor for ventricular arrhythmias and sudden cardiac death (SCD) and could indicate the presence of the potentially lethal Mendelian Long QT Syndrome (LQTS). Using a genome-wide association and replication study in up to 100,000 individuals we identified 35 common variant QT interval loci, that collectively explain ∼8-10% of QT variation and highlight the importance of calcium regulation in myocardial repolarization. Rare variant analysis of 6 novel QT loci in 298 unrelated LQTS probands identified coding variants not found in controls but of uncertain causality and therefore requiring validation. Several newly identified loci encode for proteins that physically interact with other recognized repolarization proteins. Our integration of common variant association, expression and orthogonal protein-protein interaction screens provides new insights into cardiac electrophysiology and identifies novel candidate genes for ventricular arrhythmias, LQTS,and SCD.
genome-wide association study; QT interval; Long QT Syndrome; sudden cardiac death; myocardial repolarization; arrhythmias
Calcineurin-inhibitors CI are immunosuppressive agents prescribed to patients after solid organ transplant to prevent rejection. Although these drugs have been transformative for allograft survival, long-term use is complicated by side effects including nephrotoxicity. Given the narrow therapeutic index of CI, therapeutic drug monitoring is used to prevent acute rejection from underdosing and acute toxicity from overdosing, but drug monitoring does not alleviate long-term side effects. Patients on calcineurin-inhibitors for long periods almost universally experience declines in renal function, and a subpopulation of transplant recipients ultimately develop chronic kidney disease that may progress to end stage renal disease attributable to calcineurin inhibitor toxicity (CNIT). Pharmacogenomics has the potential to identify patients who are at high risk for developing advanced chronic kidney disease caused by CNIT and providing them with existing alternate immunosuppressive therapy. In this study we utilized BioVU, Vanderbilt University Medical Center’s DNA biorepository linked to de-identified electronic medical records to identify a cohort of 115 heart transplant recipients prescribed calcineurin-inhibitors to identify genetic risk factors for CNIT We identified 37 cases of nephrotoxicity in our cohort, defining nephrotoxicity as a monthly median estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73m2 at least six months post-transplant for at least three consecutive months. All heart transplant patients were genotyped on the Illumina ADME Core Panel, a pharmacogenomic genotyping platform that assays 184 variants across 34 genes. In Cox regression analysis adjusting for age at transplant, pre-transplant chronic kidney disease, pre-transplant diabetes, and the three most significant principal components (PCAs), we did not identify any markers that met our multiple-testing threshold. As a secondary analysis we also modeled post-transplant eGFR directly with linear mixed models adjusted for age at transplant, cyclosporine use, median BMI, and the three most significant principal components. While no SNPs met our threshold for significance, a SNP previously identified in genetic studies of the dosing of tacrolimus CYP3A5 rs776746, replicated in an adjusted analysis at an uncorrected p-value of 0.02 (coeff(S.E.) = 14.60(6.41)). While larger independent studies will be required to further validate this finding, this study underscores the EMRs usefulness as a resource for longitudinal pharmacogenetic study designs.
Postoperative atrial fibrillation (PoAF) after cardiac surgery is
common and associated with increased morbidity and mortality. Increased
sympathetic activation after surgery contributes to PoAF, and beta-blockers
are the first-line recommendation for its prevention. We examined the
hypothesis that common functional genetic variants in the
β1-adrenoreceptor, the mediator of cardiac sympathetic
activation and drug target of beta-blockers, are associated with the risk
for PoAF and with the protective effect of beta-blockers.
In a prospective cohort study, we studied 947 adult European
Americans who underwent cardiac surgery at Vanderbilt University between
1999-2005. We genotyped two variants in the
β1-adrenoreceptor, rs1801253 (Arg389Gly) and rs1801252
(Ser49Gly), and used logistic regression to examine the association between
genotypes and PoAF occurring within 14 days after surgery, before and after
adjustment for demographic and clinical covariates.
PoAF occurred in 239 patients (25.2%) and was associated with
rs1801253 genotype (adjusted P=0.008), with Gly389Gly having an odds ratio
of 2.63 (95% confidence interval, 1.42 to 4.89) for PoAF compared to the
common Arg389Arg (P=0.002). In a predefined subgroup analysis, this
association appeared to be stronger among patients without beta-blocker
prophylaxis (adjusted OR=7.00; 95% CI, 1.82 to 26.96; P=0.005) compared to
patients with beta-blocker prophylaxis, among whom the association between
rs1801253 genotype and PoAF was not statistically significant (adjusted
The Gly389 variant in the β1-adrenoreceptor is
associated with PoAF, and this association appears to be modulated by
beta-blocker therapy. Future studies of the association of other adrenergic
pathway genes with PoAF will be of interest.
Platelets are enucleated cell fragments derived from megakaryocytes that play key roles in hemostasis and in the pathogenesis of atherothrombosis and cancer. Platelet traits are highly heritable and identification of genetic variants associated with platelet traits and assessing their pleiotropic effects may help to understand the role of underlying biological pathways. We conducted an electronic medical record (EMR)-based study to identify common variants that influence inter-individual variation in the number of circulating platelets (PLT) and mean platelet volume (MPV), by performing a genome-wide association study (GWAS). We characterized association of variants influencing MPV and PLT using functional, pathway and disease enrichment analysis assess pleiotropic effects of such variants by performing a phenome-wide association study (PheWAS) with a wide range of EMR-derived phenotypes. A total of 13,582 participants in the electronic MEdical Records and GEnomic (eMERGE) network had data for PLT and 6,291 participants had data for MPV. We identified 5 chromosomal regions associated with PLT and 8 associated with MPV at genome-wide significance (P<5E-8). In addition, we replicated 20 SNPs (out of 56 SNPs (α: 0.05/56=9E-4)) influencing PLT and 22 SNPs (out of 29 SNPs (α: 0.05/29=2E-3)) influencing MPV in a meta-analysis of GWAS of PLT and MPV. While our GWAS did not reveal any novel associations, our functional analyses revealed that genes in these regions influence thrombopoiesis and encode kinases, membrane proteins, proteins involved in cellular trafficking, transcription factors, proteasome complex subunits, proteins of signal transduction pathways, proteins involved in megakaryocyte development and platelet production and hemostasis. PheWAS using a single-SNP Bonferroni correction for 1368 diagnoses (0.05/1368=3.6E-5) revealed that several variants in these genes have pleiotropic associations with myocardial infarction, autoimmune and hematologic disorders. We conclude that multiple genetic loci influence interindividual variation in platelet traits and also have significant pleiotropic effects; the related genes are in multiple functional pathways including those relevant to thrombopoiesis.
Rare variants in candidate atrial fibrillation (AF) genes have been associated with AF in small kindreds. The extent to which such polymorphisms contribute to AF is unknown.
The purpose of this study was to determine the spectrum and prevalence of rare amino acid coding (AAC) variants in candidate AF genes in a large cohort of unrelated lone AF probands.
We resequenced 45 candidate genes in 303 European American (EA) lone AF probands (186 lone AF probands screened for each gene on average [range 89–303], 63 screened for all) identified in the Vanderbilt AF Registry (2002–2012). Variants detected were screened against 4300 EAs from the Exome Sequencing Project (ESP) to identify very rare (minor allele frequency ≤ 0.04%) AAC variants and these were tested for AF co-segregation in affected family members where possible.
Median age at AF onset was 46.0 years [interquartile range 33.0–54.0], and 35.6% had a family history of AF. Overall, 63 very rare AAC variants were identified in 60 of 303 lone AF probands, and 10 of 19 (52.6%) had evidence of co-segregation with AF. Among the 63 lone AF probands who had 45 genes screened, the very rare variant burden was 22%. Compared with the 4300 EA ESP, the proportion of lone AF probands with a very rare AAC variant in CASQ2 and NKX2-5 was increased 3–5-fold (P < .05).
No very rare AAC variants were identified in ~80% of lone AF probands. Potential reasons for the lack of very rare AAC variants include a complex pattern of inheritance, variants in as yet unidentified AF genes or in noncoding regions, and environmental factors.
Atrial fibrillation arrhythmia; Candidate genes; Family study; Genetic variation; Genetic epidemiology; Proarrhythmia; Rare variants
Progressive familial heart block type I (PFHBI) is a hereditary arrhythmia characterized by progressive conduction disturbances in the His-Purkinje system. PFHBI has been linked to genes such as SCN5A that influence cardiac excitability, but not to genes that influence cell-to-cell communication. Our goal was to explore whether nucleotide substitutions in genes coding for connexin proteins would associate with clinical cases of PFHBI and if so, to establish a genotype-cell phenotype correlation for that mutation.
Methods and Results
We screened 156 probands afflicted with PFHBI. In addition to 12 sodium channel mutations, we found a germline GJA5 (connexin40; Cx40) mutation (Q58L) in an afflicted family. Heterologous expression of Cx40-Q58L in connexin-deficient neuroblastoma cells resulted in marked reduction of junctional conductance (Cx40-WT: 22.2±1.7 nS, n=14; Cx40-Q58L: 0.56±0.34 nS, n=14; p<0.001) and diffuse localization of immunoreactive proteins in the vicinity of the plasma membrane without formation of gap junctions. Heteromeric co-transfection of Cx40-WT and Cx40-Q58L resulted in homogenous distribution of proteins in the plasma membrane rather than in membrane plaques in about 50% of cells; well-defined gap junctions were observed in other cells. Junctional conductance values correlated with the distribution of gap junction plaques.
Mutation Cx40-Q58L impairs gap junction formation at cell-cell interfaces. This is the first demonstration of a germline mutation in a connexin gene that associates with inherited ventricular arrhythmias, and emphasizes the importance of Cx40 in normal propagation in the specialized conduction system.
heart block; genes; ion channels; sudden death; gap junctions
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 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 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 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.
pharmacogenomics; sudden cardiac death; adverse drug reaction; next generation sequencing
To test the hypothesis that rare variants are associated with Drug-induced long QT syndrome (diLQTS) and torsade de pointes (TdP).
diLQTS is associated with the potentially fatal arrhythmia TdP. The contribution of rare genetic variants to the underlying genetic framework predisposing diLQTS has not been systematically examined.
We performed whole exome sequencing (WES) on 65 diLQTS cases and 148 drug-exposed controls of European descent. We employed rare variant analyses (variable threshold [VT] and sequence kernel association test [SKAT]) and gene-set analyses to identify genes enriched with rare amino-acid coding (AAC) variants associated with diLQTS. Significant associations were reanalyzed by comparing diLQTS cases to 515 ethnically matched controls from the NHLBI GO Exome Sequencing Project (ESP).
Rare variants in 7 genes were enriched in the diLQTS cases according to SKAT or VT compared to drug exposed controls (p<0.001). Of these, we replicated the diLQTS associations for KCNE1 and ACN9 using 515 ESP controls (p<0.05). A total of 37% of the diLQTS cases also had ≥1 rare AAC variant, as compared to 21% of controls (p=0.009), in a predefined set of seven congenital LQTS (cLQTS) genes encoding potassium channels or channel modulators (KCNE1,KCNE2,KCNH2,KCNJ2, KCNJ5,KCNQ1,AKAP9).
By combining WES with aggregated rare variant analyses, we implicate rare variants in KCNE1 and ACN9 as risk factors for diLQTS. Moreover, diLQTS cases were more burdened by rare AAC variants in cLQTS genes encoding potassium channel modulators, supporting the idea that multiple rare variants, notably across cLQTS genes, predispose to diLQTS.
exome; torsade des pointes; long QT syndrome; genetics, adverse drug event
Large-scale biorepositories that couple biologic specimens with electronic health records containing documentation of phenotypic expression can accelerate scientific research and discovery. However, differences between those subjects who participate in biorepository-based research and the population from which they are drawn may influence research validity. While an opt-out approach to biorepository-based research enhances inclusiveness, empirical research evaluating voluntariness, risk, and the feasibility of an opt-out approach is sparse, and factors influencing patients’ decisions to opt out are understudied. Determining why patients choose to opt out may help to improve voluntariness, however there may be ethical and logistical challenges to studying those who opt out. In this perspective paper, the authors explore what is known about research based on the opt-out model, describe a large-scale biorepository that leverages the opt-out model, and review specific ethical and logistical challenges to bridging the research gaps that remain.
Medical Records Systems, Computerized; Medical Informatics Computing; Informed Consent; Support, U.S. Gov’t, P.H.S.; Biorepositories; Biomedical Ethics
A prolonged QT interval is associated with increased risk of Torsades de pointes (TdP) and may be fatal. We sought to investigate the extent to which clinical covariates affect the change in QT interval among ‘real-world’ patients treated with sotalol and followed in an electronic medical record (EMR) system.
Methods and results
We used clinical alerts in our EMR system to identify all patients in whom a new prescription for sotalol was written (2001–11). Rate-corrected QT (QTc) was calculated by Bazett's formula. Correlates of sotalol-induced change in the QTc interval and sotalol discontinuation were examined using linear and logistic regression, respectively. Overall, 541 sotalol-exposed patients were identified (n = 200 women, 37%). The mean first sotalol dose was 86 ± 39 mg, age 64 ± 13 years, and BMI 30 ± 7 kg/m2. Atrial fibrillation/flutter was the predominant indication (92.2%). After initial exposure, the change in the QTc interval from baseline was highly variable: ΔQTc after 2 h = 3 ± 42 ms (P = 0.17) and 11 ± 37 ms after ≥48 h (P < 0.001). Multivariable linear regression analysis identified female gender and age, reduced left ventricular ejection fraction, high sotalol dose, hypertrophic cardiomyopathy, and loop diuretic co-administration as correlates of increased ΔQTc at ≥48 h (P < 0.05 for all). Within 3 days of initiation, 12% discontinued sotalol of which 31% were because of exaggerated QTc prolongation. One percent developed TdP.
In this EMR-based cohort, the increase in QTc with sotalol initiation was highly variable, and multiple clinical factors contributed. These data represent an important step in ongoing work to identify real-world patients likely to tolerate long-term therapy and reinforces the utility of EMR-based cohorts as research tools.
Arrhythmia; Long QT syndrome; Torsades de pointes; Beta-blocker; Atrial fibrillation; Electronic medical records
Thyroid stimulating hormone (TSH) hormone levels are normally tightly regulated within an individual; thus, relatively small variations may indicate thyroid disease. Genome-wide association studies (GWAS) have identified variants in PDE8B and FOXE1 that are associated with TSH levels. However, prior studies lacked racial/ethnic diversity, limiting the generalization of these findings to individuals of non-European ethnicities. The Electronic Medical Records and Genomics (eMERGE) Network is a collaboration across institutions with biobanks linked to electronic medical records (EMRs). The eMERGE Network uses EMR-derived phenotypes to perform GWAS in diverse populations for a variety of phenotypes. In this report, we identified serum TSH levels from 4,501 European American and 351 African American euthyroid individuals in the eMERGE Network with existing GWAS data. Tests of association were performed using linear regression and adjusted for age, sex, body mass index (BMI), and principal components, assuming an additive genetic model. Our results replicate the known association of PDE8B with serum TSH levels in European Americans (rs2046045 p = 1.85×10−17, β = 0.09). FOXE1 variants, associated with hypothyroidism, were not genome-wide significant (rs10759944: p = 1.08×10−6, β = −0.05). No SNPs reached genome-wide significance in African Americans. However, multiple known associations with TSH levels in European ancestry were nominally significant in African Americans, including PDE8B (rs2046045 p = 0.03, β = −0.09), VEGFA (rs11755845 p = 0.01, β = −0.13), and NFIA (rs334699 p = 1.50×10−3, β = −0.17). We found little evidence that SNPs previously associated with other thyroid-related disorders were associated with serum TSH levels in this study. These results support the previously reported association between PDE8B and serum TSH levels in European Americans and emphasize the need for additional genetic studies in more diverse populations.
Electrocardiographic QRS duration, a measure of cardiac intraventricular conduction, varies ~2-fold in individuals without cardiac disease. Slow conduction may promote reentrant arrhythmias.
Methods and Results
We performed a genome-wide association study (GWAS) to identify genomic markers of QRS duration in 5,272 individuals without cardiac disease selected from electronic medical record (EMR) algorithms at five sites in the Electronic Medical Records and Genomics (eMERGE) network. The most significant loci were evaluated within the CHARGE consortium QRS GWAS meta-analysis. Twenty-three single nucleotide polymorphisms in 5 loci, previously described by CHARGE, were replicated in the eMERGE samples; 18 SNPs were in the chromosome 3 SCN5A and SCN10A loci, where the most significant SNPs were rs1805126 in SCN5A with p=1.2×10−8 (eMERGE) and p=2.5×10−20 (CHARGE) and rs6795970 in SCN10A with p=6×10−6 (eMERGE) and p=5×10−27 (CHARGE). The other loci were in NFIA, near CDKN1A, and near C6orf204. We then performed phenome-wide association studies (PheWAS) on variants in these five loci in 13,859 European Americans to search for diagnoses associated with these markers. PheWAS identified atrial fibrillation and cardiac arrhythmias as the most common associated diagnoses with SCN10A and SCN5A variants. SCN10A variants were also associated with subsequent development of atrial fibrillation and arrhythmia in the original 5,272 “heart-healthy” study population.
We conclude that DNA biobanks coupled to EMRs provide a platform not only for GWAS but may also allow broad interrogation of the longitudinal incidence of disease associated with genetic variants. The PheWAS approach implicated sodium channel variants modulating QRS duration in subjects without cardiac disease as predictors of subsequent arrhythmias.
cardiac conduction; QRS duration; atrial fibrillation; genome-wide association study; phenome-wide association study; electronic medical records
The use of electronic medical record data linked to biological specimens in health care settings is expected to enable cost-effective and rapid genomic analyses. Here, we present a model that highlights potential advantages for genomic discovery and describe the operational infrastructure that facilitated multiple simultaneous discovery efforts.
Editorials; arrhythmias; cardiac; genetics; humans; pharmacology; stem cells
Responses to drug therapy vary from benefit to no effect to adverse effects which can be serious or occasionally fatal. Increasing evidence supports the idea that genetic variants can play a major role in this spectrum of responses. Well-studied examples in cardiovascular therapeutics include predictors of steady-state warfarin dosage, predictors of reduced efficacy among patients receiving clopidogrel for drug eluting stents, and predictors of some serious adverse drug effects. This review summarizes contemporary approaches to identifying and validating genetic predictors of variability in response to drug treatment. Approaches to incorporating this new knowledge into clinical care, and the barriers to this concept, are addressed.
Purpose of review
To survey genetic variation contributing to variable responsiveness and toxicity to important cardiovascular drugs and highlight recent developments in the field of cardiovascular pharmacogenomics and personalized medicine.
Previously recognized pharmacogenomic associations with drug efficacy have been further validated (e.g. with clopidogrel and warfarin) and shown to influence clinically important outcomes. The clinical significance of variants modulating toxicity (e.g. SLCO1B1 with simvastatin) has also been confirmed. The genetic contribution to variable efficacy and toxicity of other important classes of cardiovascular drugs, such as beta-blockers, is becoming increasingly recognized. Prospective trials testing whether the use of genomic information improves clinical care are underway. Guidance based on the most well-established pharmacogenomic findings has appeared in prescribing labeling and is in the early stages of being implemented into routine clinical care.
Clinically validated gene variants that modulate responsiveness to cardiovascular drugs continue to be discovered and validated. Early steps are underway to translate these discoveries into clinical care.
personalized medicine; pharmacogenomics; variable drug response
Simvastatin is among the most commonly used prescription medications for cholesterol reduction. A single coding SNP, rs4149056T>C, in SLCO1B1 increases systemic exposure to simvastatin and the risk of muscle toxicity. We summarize evidence from the literature supporting this association and provide therapeutic recommendations for simvastatin based on SLCO1B1 genotype. This document is an update to the 2012 Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for SLCO1B1 and simvastatin-induced myopathy.
pharmacogenetics; pharmacogenomics; myalgias; rhabdomyolysis; CPIC; SLCO1B1; simvastatin
Brugada syndrome is a rare cardiac arrhythmia disorder, causally related to SCN5A mutations in around 20% of cases1–3. Through a genome-wide association study of 312 individuals with Brugada syndrome and 1,115 controls, we detected 2 significant association signals at the SCN10A locus (rs10428132) and near the HEY2 gene (rs9388451). Independent replication confirmed both signals (meta-analyses: rs10428132, P = 1.0 × 10−68; rs9388451, P = 5.1 × 10−17) and identified one additional signal in SCN5A (at 3p21; rs11708996, P = 1.0 × 10−14). The cumulative effect of the three loci on disease susceptibility was unexpectedly large (Ptrend = 6.1 × 10−81). The association signals at SCN5A-SCN10A demonstrate that genetic polymorphisms modulating cardiac conduction4–7 can also influence susceptibility to cardiac arrhythmia. The implication of association with HEY2, supported by new evidence that Hey2 regulates cardiac electrical activity, shows that Brugada syndrome may originate from altered transcriptional programming during cardiac development8. Altogether, our findings indicate that common genetic variation can have a strong impact on the predisposition to rare diseases.
VKORC1 and CYP2C9 are important contributors to warfarin dose variability, but explain less variability for individuals of African descent than for those of European or Asian descent. We aimed to identify additional variants contributing to warfarin dose requirements in African Americans.
We did a genome-wide association study of discovery and replication cohorts. Samples from African-American adults (aged ≥18 years) who were taking a stable maintenance dose of warfarin were obtained at International Warfarin Pharmacogenetics Consortium (IWPC) sites and the University of Alabama at Birmingham (Birmingham, AL, USA). Patients enrolled at IWPC sites but who were not used for discovery made up the independent replication cohort. All participants were genotyped. We did a stepwise conditional analysis, conditioning first for VKORC1 −1639G→A, followed by the composite genotype of CYP2C9*2 and CYP2C9*3. We prespecified a genome-wide significance threshold of p<5×10−8 in the discovery cohort and p<0·0038 in the replication cohort.
The discovery cohort contained 533 participants and the replication cohort 432 participants. After the prespecified conditioning in the discovery cohort, we identified an association between a novel single nucleotide polymorphism in the CYP2C cluster on chromosome 10 (rs12777823) and warfarin dose requirement that reached genome-wide significance (p=1·51×10−8). This association was confirmed in the replication cohort (p=5·04×10−5); analysis of the two cohorts together produced a p value of 4·5×10−12. Individuals heterozygous for the rs12777823 A allele need a dose reduction of 6·92 mg/week and those homozygous 9·34 mg/week. Regression analysis showed that the inclusion of rs12777823 significantly improves warfarin dose variability explained by the IWPC dosing algorithm (21% relative improvement).
A novel CYP2C single nucleotide polymorphism exerts a clinically relevant effect on warfarin dose in African Americans, independent of CYP2C9*2 and CYP2C9*3. Incorporation of this variant into pharmacogenetic dosing algorithms could improve warfarin dose prediction in this population.
National Institutes of Health, American Heart Association, Howard Hughes Medical Institute, Wisconsin Network for Health Research, and the Wellcome Trust.
Phenome-wide association studies (PheWAS) have demonstrated utility in validating genetic associations derived from traditional genetic studies as well as identifying novel genetic associations. Here we used an electronic health record (EHR)-based PheWAS to explore pleiotropy of genetic variants in the fat mass and obesity associated gene (FTO), some of which have been previously associated with obesity and type 2 diabetes (T2D). We used a population of 10,487 individuals of European ancestry with genome-wide genotyping from the Electronic Medical Records and Genomics (eMERGE) Network and another population of 13,711 individuals of European ancestry from the BioVU DNA biobank at Vanderbilt genotyped using Illumina HumanExome BeadChip. A meta-analysis of the two study populations replicated the well-described associations between FTO variants and obesity (odds ratio [OR] = 1.25, 95% Confidence Interval = 1.11–1.24, p = 2.10 × 10−9) and FTO variants and T2D (OR = 1.14, 95% CI = 1.08–1.21, p = 2.34 × 10−6). The meta-analysis also demonstrated that FTO variant rs8050136 was significantly associated with sleep apnea (OR = 1.14, 95% CI = 1.07–1.22, p = 3.33 × 10−5); however, the association was attenuated after adjustment for body mass index (BMI). Novel phenotype associations with obesity-associated FTO variants included fibrocystic breast disease (rs9941349, OR = 0.81, 95% CI = 0.74–0.91, p = 5.41 × 10−5) and trends toward associations with non-alcoholic liver disease and gram-positive bacterial infections. FTO variants not associated with obesity demonstrated other potential disease associations including non-inflammatory disorders of the cervix and chronic periodontitis. These results suggest that genetic variants in FTO may have pleiotropic associations, some of which are not mediated by obesity.
PheWAS; genetic association; pleiotropy; Exome chip; FTO; BMI
Variable function and expression of drug transporters have been proposed as mechanisms contributing to variable response to drug therapy. Block of the HERG channel, encoding IKr, can lead to serious arrhythmias, and a key drug-blocking site in HERG has been identified on the intracellular face of the pore. We begin to advance the hypothesis that active drug uptake enhances IKr block.
Methods and Results
Reverse transcriptase–polymerase chain reaction identified expression in the human atrium and ventricle of 14 of 31 candidate drug uptake and efflux transporters, including OCTN1 (SLC22A4), a known uptake transporter of the HERG channel blocker quinidine. In situ hybridization and immunostaining localized OCTN1 expression to cardiomyocytes. The IC50 for quinidine block of IKr in CHO cells transfected with HERG alone was significantly higher than cells transfected with HERG + OCTN1 (0.66 ± 0.15 μM versus 0.14 ± 0.06 μM [52% absolute increase in drug block; 95% confidence interval, 0.4–0.64 μM]), and this effect was further potentiated by a common genetic variant of OCTN1, L503F. In the absence of OCTN1, quinidine block could be 91% ± 5% washed out, but with the transporter, washout was incomplete (57% ± 6%). OCTN1 coexpression also facilitated HERG block by flecainide and ibutilide, but not erythromycin.
Coexpression of the organic cation transporter, OCTN1, expressed in human cardiac myocytes, intensifies quinidine-induced HERG block. These findings establish a critical hypothesis that variable drug transporter activity may be a potential risk factor for torsade de pointes.
antiarrhythmia agents; arrhythmia; pharmacology; pharmacokinetics; ion channels
As genotyping technology has progressed, genome-wide association studies (GWAS) have matured into efficient and effective tools for mapping genes underlying human phenotypes. Recent studies have demonstrated the utility of the GWAS approach for examining pharmacogenomic traits, including drug metabolism, efficacy, and toxicity. Application of GWAS to pharmacogenomic outcomes presents unique challenges and opportunities. In the current review, we discuss the potential promises and potential caveats of this approach specifically as it relates to pharmacogenomic studies. Concerns with study design, power and sample size, and analysis are reviewed. We further examine the features of successful pharmacogenomic GWAS, and describe consortia efforts that are likely to expand the reach of pharmacogenomic GWAS in the future.
Genome-wide association; GWAS; pharmacogenetic; pharmacogenomic; drug response; drug metabolism; toxicity
Whole exome sequencing (WES) is a powerful technique for Mendelian disease gene discovery. However, variant prioritization remains a challenge. We applied WES to identify the causal variant in a large family with familial dilated cardiomyopathy (DMC) of unknown etiology.
Methods and Results
A large family with autosomal dominant, familial DCM was identified. Exome capture and sequencing was performed in 3 remotely related, affected subjects predicted to share <0.1% of their genomes by descent. Shared variants were filtered for rarity, evolutionary conservation, and predicted functional significance, and remaining variants were filtered against 71 locally generated exomes. Variants were also prioritized using the Variant Annotation Analysis and Search Tool (VAAST). Final candidates were validated by Sanger sequencing and tested for segregation. There were 664 shared heterozygous nonsense, missense, or splice site variants, of which 26 were rare (minor allele frequency ≤ 0.001 or not reported) in two public databases. Filtering against internal exomes reduced the number of candidates to 2, and of these, a single variant (c.1907 G>A) in RBM20, segregated with disease status and was absent in unaffected internal reference exomes. Bioinformatic prioritization with VAAST supported this result.
WES of remotely related DCM subjects from a large, multiplex family, followed by systematic filtering, identified a causal RBM20 mutation without the need for linkage analysis.
genetic heart disease; exome; congestive heart failure