Jason D. Roberts

Meta-analysis identifies six new susceptibility loci for atrial fibrillation

Atrial fibrillation is a highly prevalent arrhythmia and a major risk factor for stroke, heart failure and death. We conducted a genome-wide association study (GWAS) in individuals of European ancestry, including 6,707 with and 52,426 without atrial fibrillation. Six new atrial fibrillation susceptibility loci were identified and replicated in an additional sample of individuals of European ancestry, including 5,381 subjects with and 10,030 subjects without atrial fibrillation (P < 5 × 10−8). Four of the loci identified in Europeans were further replicated in silico in a GWAS of Japanese individuals, including 843 individuals with and 3,350 individuals without atrial fibrillation. The identified loci implicate candidate genes that encode transcription factors related to cardiopulmonary development, cardiac-expressed ion channels and cell signaling molecules.

Point-of-care genetic testing for personalisation of antiplatelet treatment (RAPID GENE): a prospective, randomised, proof-of-concept trial

BACKGROUND Prospective assessment of pharmacogenetic strategies has been limited by an inability to undertake bedside genetic testing. The CYP2C19*2 allele is a common genetic variant associated with increased rates of major adverse events in individuals given clopidogrel after percutaneous coronary intervention (PCI). We used a novel point-of-care genetic test to identify carriers of the CYP2C19*2 allele and aimed to assess a pharmacogenetic approach to dual antiplatelet treatment after PCI. METHODS Between Aug 26, 2010, and July 7, 2011, 200 patients were enrolled into our prospective, randomised, proof-of-concept study. Patients undergoing PCI for acute coronary syndrome or stable angina were randomly assigned to rapid point-of-care genotyping or to standard treatment. Individuals in the rapid genotyping group were screened for the CYP2C19*2 allele. Carriers were given 10 mg prasugrel daily, and non-carriers and patients in the standard treatment group were given 75 mg clopidogrel daily. The primary endpoint was the proportion of CYP2C19*2 carriers with high on-treatment platelet reactivity (P2Y12 reactivity unit [PRU] value of more than 234) after 1 week of dual antiplatelet treatment, which is a marker associated with increased adverse cardiovascular events. Interventional cardiologists and data analysts were masked to genetic status and treatment. Patients were not masked to treatment allocation. All analyses were by intention to treat. This study is registered with ClinicalTrials.gov, NCT01184300. FINDINGS After randomisation, 187 patients completed follow-up (91 rapid genotyping group, 96 standard treatment). 23 individuals in each group carried at least one CYP2C19*2 allele. None of the 23 carriers in the rapid genotyping group had a PRU value of more than 234 at day 7, compared with seven (30%) given standard treatment (p=0·0092). The point-of-care genetic test had a sensitivity of 100% (95% CI 92·3-100) and a specificity of 99·3% (96·3-100). INTERPRETATION Point-of-care genetic testing after PCI can be done effectively at the bedside and treatment of identified CYP2C19*2 carriers with prasugrel can reduce high on-treatment platelet reactivity. FUNDING Spartan Biosciences.

The Short QT Syndrome : Proposed Diagnostic Criteria

OBJECTIVES We aimed to develop diagnostic criteria for the short QT syndrome (SQTS) to facilitate clinical evaluation of suspected cases. BACKGROUND The SQTS is a cardiac channelopathy associated with atrial fibrillation and sudden cardiac death. Ten years after its original description, a consensus regarding an appropriate QT interval cutoff and specific diagnostic criteria have yet to be established. METHODS The MEDLINE database was searched for all reported cases of SQTS in the English language, and all relevant data were extracted. The distribution of QT intervals and electrocardiographic (ECG) features in affected cases were analyzed and compared to data derived from ECG analysis from general population studies. RESULTS A total of 61 reported cases of SQTS were identified. Index events, including sudden cardiac death, aborted cardiac arrest, syncope, and/or atrial fibrillation occurred in 35 of 61 (57.4%) cases. The cohort was predominantly male (75.4%) and had a mean QT(c) value of 306.7 ms with values ranging from 248 to 381 ms in symptomatic cases. In reference to the ECG characteristics of the general population, and in consideration of clinical presentation, family history, and genetic findings, a highly sensitive diagnostic scoring system was developed. CONCLUSIONS Based on a comprehensive review of 61 reported cases of the SQTS, formal diagnostic criteria have been proposed that will facilitate diagnostic evaluation in suspected cases of SQTS. Diagnostic criteria may lead to a greater recognition of this condition and provoke screening of at-risk family members.

Clinical ResearchHeart Rhythm DisorderThe Short QT Syndrome: Proposed Diagnostic Criteria

OBJECTIVES We aimed to develop diagnostic criteria for the short QT syndrome (SQTS) to facilitate clinical evaluation of suspected cases. BACKGROUND The SQTS is a cardiac channelopathy associated with atrial fibrillation and sudden cardiac death. Ten years after its original description, a consensus regarding an appropriate QT interval cutoff and specific diagnostic criteria have yet to be established. METHODS The MEDLINE database was searched for all reported cases of SQTS in the English language, and all relevant data were extracted. The distribution of QT intervals and electrocardiographic (ECG) features in affected cases were analyzed and compared to data derived from ECG analysis from general population studies. RESULTS A total of 61 reported cases of SQTS were identified. Index events, including sudden cardiac death, aborted cardiac arrest, syncope, and/or atrial fibrillation occurred in 35 of 61 (57.4%) cases. The cohort was predominantly male (75.4%) and had a mean QT(c) value of 306.7 ms with values ranging from 248 to 381 ms in symptomatic cases. In reference to the ECG characteristics of the general population, and in consideration of clinical presentation, family history, and genetic findings, a highly sensitive diagnostic scoring system was developed. CONCLUSIONS Based on a comprehensive review of 61 reported cases of the SQTS, formal diagnostic criteria have been proposed that will facilitate diagnostic evaluation in suspected cases of SQTS. Diagnostic criteria may lead to a greater recognition of this condition and provoke screening of at-risk family members.

Impact of Genetic Discoveries on the Classification of Lone Atrial Fibrillation

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, represents a major burden to patients and health care systems through its sequelae of heart failure and stroke. Its age-dependent increase in prevalence has led to worrisome predictions of an expanding burden secondary to our aging population. This growing epidemic is further exacerbated by a current lack of highly effective therapies for the arrhythmia stemming from our incomplete understanding of its complex pathophysiology. Recent genetic studies, triggered in part by evidence of a hereditary component of AF, have begun to identify predisposing genes and offer further insights into the mechanisms of lone AF. A variety of ion channels and most recently a circulating hormone have been implicated. The apparent genetic diversity underlying the arrhythmia has served to emphasize the heterogeneity of factors that govern its initiation and maintenance. The different causative genes seem to predispose to AF through distinct putative mechanisms, including enhanced and delayed atrial action potential repolarization, cellular hyperexcitability, and conduction velocity heterogeneity. Classification of lone AF into mechanistic subgroups serves to emphasize its heterogeneity and has the potential to guide developmental and clinical treatment strategies. The frequent recalcitrant nature of the arrhythmia to contemporary pharmacological and invasive therapies may be overcome through an ability to identify, through genetics, the mechanistic subclass of AF for an individual patient. Proper identification of the culprit pathophysiology may permit administration of a targeted form of therapy that carries maximal efficacy and minimal risk in a manner consistent with the vision of pharmacogenomics.

Evaluation of non-synonymous NPPA single nucleotide polymorphisms in atrial fibrillation

AIMS Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, is an important cause of morbidity and mortality. A genetic mutation in the NPPA gene, which encodes the atrial natriuretic peptide, has been identified as the putative causative factor in a family with an autosomal dominant pattern of inheritance for AF. Two common single nucleotide polymorphisms (SNPs) in NPPA, rs5063 and rs5065, result in amino acid changes of the primary peptide and have been previously implicated in conditions associated with AF, including stroke and hypertension. Recently, the rs5063 SNP has been reported to confer an increased risk of AF development in a Chinese population. We sought to examine the associations of both rs5063 and rs5065 with AF in two separate North American cohorts of European ancestry. METHODS AND RESULTS Patients with early-onset AF, along with healthy controls, were recruited at the University of Ottawa Heart Institute (UOHI) and the Massachusetts General Hospital (MGH). Study participants were genotyped for rs5063 and rs5065 using a combination of restriction fragment length polymorphism analysis and DNA microarrays. The study genotyped a total of 620 AF cases and 2446 healthy controls. The UOHI arm of the study identified an odds ratio (OR) of 0.72 [95% confidence interval (CI): 0.42-1.24] for rs5063, whereas an OR of 1.33 (95% CI: 0.80-2.21) was observed in the MGH arm. The combined OR approximated unity (OR 0.99; 95% CI: 0.54-1.80). Analysis of rs5065 revealed an OR of 1.12 (95% CI: 0.84-1.48) in UOHI, 1.08 (95% CI 0.80-1.45) in MGH, and 1.10 (95% CI 0.90-1.35) when combined. CONCLUSION Common non-synonymous genetic variants within NPPA in these two large North American cohorts of European ancestry are not associated with the development of AF.

Inherited cardiomyopathies mimicking arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) represents an inherited cardiomyopathy that manifests clinically with malignant ventricular arrhythmias, sudden cardiac death, and less commonly heart failure. The condition is characterized by replacement of the myocardium, primarily of the right ventricle, with fibrofatty tissue. Extensive fibrofatty replacement of the myocardium has been previously thought to be pathognomonic of ARVC; however, this report details two other forms of inherited cardiomyopathy, namely hypertrophic cardiomyopathy (HCM) and the PRKAG2 cardiac syndrome, that were found to have significant fibrofatty myocardial replacement at pathologic examination. This report represents the first documentation of inherited cardiomyopathies mimicking ARVC and highlights the concept that other cardiac conditions can be associated with fibrofatty replacement of the myocardium.

A prospective randomized evaluation of a pharmacogenomic approach to antiplatelet therapy among patients with ST-elevation myocardial infarction: the RAPID STEMI study.

Treatment of carriers of the CYP2C19*2 allele and ABCB1 TT genotype with clopidogrel is associated with increased ischemic complications after percutaneous coronary intervention (PCI). We sought to evaluate a pharmacogenomic strategy among patients undergoing PCI for ST-elevation myocardial infarction (STEMI), by performing a randomized trial, enrolling 102 patients. Point-of-care genetic testing for CYP2C19*2, ABCB1 TT and CYP2C19*17 was performed with carriers of either the CYP2C19*2 allele or ABCB1 TT genotype randomly assigned to a strategy of prasugrel 10 mg daily or an augmented dosing strategy of clopidogrel (150 mg daily for 6 days then 75 mg daily). The primary end point was the proportion of at-risk carriers exhibiting high on-treatment platelet reactivity (HPR), a marker associated with increased adverse cardiovascular events, after 1 month. Fifty-nine subjects (57.8%) were identified as carriers of at least one at-risk variant. Treatment with prasugrel significantly reduced HPR compared with clopidogrel by P2Y12 reaction unit (PRU) thresholds of >234 (0 vs 24.1%, P=0.0046) and PRU>208 (3.3 vs 34.5%, P=0.0025). The sensitivity of point-of-care testing was 100% (95% CI 88.0–100), 100% (86.3–100) and 96.9% (82.0–99.8) and specificity was 97.0% (88.5–99.5), 97.1% (89.0–99.5) and 98.5% (90.9–99.9) for identifying CYP2C19*2, ABCB1 TT and CYP2C19*17, respectively. Logistic regression confirmed carriers as a strong predictor of HPR (OR=6.58, 95% CI 1.24–34.92; P=0.03). We confirmed that concurrent identification of three separate genetic variants in patients with STEMI receiving PCI is feasible at the bedside. Among carriers of at-risk genotypes, treatment with prasugrel was superior to an augmented dosing strategy of clopidogrel in reducing HPR.

Genetic Investigation Into the Differential Risk of Atrial Fibrillation Among Black and White Individuals

IMPORTANCE White persons have a higher risk of atrial fibrillation (AF) compared with black individuals despite a lower prevalence of risk factors. This difference may be due, at least in part, to genetic factors. OBJECTIVES To determine whether 9 single-nucleotide polymorphisms (SNPs) associated with AF account for this paradoxical differential racial risk for AF and to use admixture mapping to search genome-wide for loci that may account for this phenomenon. DESIGN, SETTING, AND PARTICIPANTS Genome-wide admixture analysis and candidate SNP study involving 3 population-based cohort studies that were initiated between 1987 and 1997, including the Cardiovascular Health Study (CHS) (n = 4173), the Atherosclerosis Risk in Communities (ARIC) (n = 12 341) study, and the Health, Aging, and Body Composition (Health ABC) (n = 1015) study. In all 3 studies, race was self-identified. Cox proportional hazards regression models and the proportion of treatment effect method were used to determine the impact of 9 AF-risk SNPs among participants from CHS and the ARIC study. The present study began July 1, 2012, and was completed in 2015. MAIN OUTCOMES AND MEASURES Incident AF systematically ascertained using clinic visit electrocardiograms, hospital discharge diagnosis codes, death certificates, and Medicare claims data. RESULTS A single SNP, rs10824026 (chromosome 10: position 73661450), was found to significantly mediate the higher risk for AF in white participants compared with black participants in CHS (11.4%; 95% CI, 2.9%-29.9%) and ARIC (31.7%; 95% CI, 16.0%-53.0%). Admixture mapping was performed in a meta-analysis of black participants within CHS (n = 811), ARIC (n = 3112), and Health ABC (n = 1015). No loci that reached the prespecified statistical threshold for genome-wide significance were identified. CONCLUSIONS AND RELEVANCE The rs10824026 SNP on chromosome 10q22 mediates a modest proportion of the increased risk of AF among white individuals compared with black individuals, potentially through an effect on gene expression levels of MYOZ1. No additional genetic variants accounting for a significant portion of the differential racial risk of AF were identified with genome-wide admixture mapping, suggesting that additional genetic or environmental influences beyond single SNPs in isolation may account for the paradoxical racial risk of AF among white individuals and black individuals.

Targeted Deep Sequencing Reveals No Definitive Evidence for Somatic Mosaicism in Atrial Fibrillation

Background—Studies of ⩽15 atrial fibrillation (AF) patients have identified atrial-specific mutations within connexin genes, suggesting that somatic mutations may account for sporadic cases of the arrhythmia. We sought to identify atrial somatic mutations among patients with and without AF using targeted deep next-generation sequencing of 560 genes, including genetic culprits implicated in AF, the Mendelian cardiomyopathies and channelopathies, and all ion channels within the genome. Methods and Results—Targeted gene capture and next-generation sequencing were performed on DNA from lymphocytes and left atrial appendages of 34 patients (25 with AF). Twenty AF patients had undergone cardiac surgery exclusively for pulmonary vein isolation and 17 had no structural heart disease. Sequence alignment and variant calling were performed for each atrial–lymphocyte pair using the Burrows–Wheeler Aligner, the Genome Analysis Toolkit, and MuTect packages. Next-generation sequencing yielded a median 265-fold coverage depth (interquartile range, 64–369). Comparison of the 3 million base pairs from each atrial–lymphocyte pair revealed a single potential somatic missense mutation in 3 AF patients and 2 in a single control (12 versus 11%; P=1). All potential discordant variants had low allelic fractions (range, 2.3%–7.3%) and none were detected with conventional sequencing. Conclusions—Using high-depth next-generation sequencing and state-of-the art somatic mutation calling approaches, no pathogenic atrial somatic mutations could be confirmed among 25 AF patients in a comprehensive cardiac arrhythmia genetic panel. These findings indicate that atrial-specific mutations are rare and that somatic mosaicism is unlikely to exert a prominent role in AF pathogenesis.