Steven A. Lubitz

Common variants in KCNN3 are associated with lone atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia. Previous studies have identified several genetic loci associated with typical AF. We sought to identify common genetic variants underlying lone AF. This condition affects a subset of individuals without overt heart disease and with an increased heritability of AF. We report a meta-analysis of genome-wide association studies conducted using 1,335 individuals with lone AF (cases) and 12,844 unaffected individuals (referents). Cases were obtained from the German AF Network, Heart and Vascular Health Study, the Atherosclerosis Risk in Communities Study, the Cleveland Clinic and Massachusetts General Hospital. We identified an association on chromosome 1q21 to lone AF (rs13376333, adjusted odds ratio = 1.56; P = 6.3 × 10−12), and we replicated this association in two independent cohorts with lone AF (overall combined odds ratio = 1.52, 95% CI 1.40–1.64; P = 1.83 × 10−21). rs13376333 is intronic to KCNN3, which encodes a potassium channel protein involved in atrial repolarization.

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.

Genome-wide association study of PR interval

The electrocardiographic PR interval (or PQ interval) reflects atrial and atrioventricular nodal conduction, disturbances of which increase risk of atrial fibrillation. We report a meta-analysis of genome-wide association studies for PR interval from seven population-based European studies in the CHARGE Consortium: AGES, ARIC, CHS, FHS, KORA, Rotterdam Study, and SardiNIA (N = 28,517). We identified nine loci associated with PR interval at P < 5 × 10−8. At the 3p22.2 locus, we observed two independent associations in voltage-gated sodium channel genes, SCN10A and SCN5A. Six of the loci were near cardiac developmental genes, including CAV1-CAV2, NKX2-5 (CSX1), SOX5, WNT11, MEIS1, and TBX5-TBX3, providing pathophysiologically interesting candidate genes. Five of the loci, SCN5A, SCN10A, NKX2-5, CAV1-CAV2, and SOX5, were also associated with atrial fibrillation (N = 5,741 cases, P < 0.0056). This suggests a role for common variation in ion channel and developmental genes in atrial and atrioventricular conduction as well as in susceptibility to atrial fibrillation.

Variants in ZFHX3 are associated with atrial fibrillation in individuals of European ancestry

We conducted meta-analyses of genome-wide association studies for atrial fibrillation (AF) in participants from five community-based cohorts. Meta-analyses of 896 prevalent (15,768 referents) and 2,517 incident (21,337 referents) AF cases identified a new locus for AF (ZFHX3, rs2106261, risk ratio RR = 1.19; P = 2.3 × 10−7). We replicated this association in an independent cohort from the German AF Network (odds ratio = 1.44; P = 1.6 × 10−11; combined RR = 1.25; combined P = 1.8 × 10−15).

50 year trends in atrial fibrillation prevalence, incidence, risk factors, and mortality in the Framingham Heart Study: a cohort study

BACKGROUND Comprehensive long-term data on atrial fibrillation trends in men and women are scant. We aimed to provide such data through analysis of the Framingham cohort over 50 years. METHODS We investigated trends in incidence, prevalence, and risk factors for atrial fibrillation and its association with stroke and mortality after onset in 9511 participants enrolled in the Framingham Heart Study between 1958 and 2007. We analysed trends within 10 year groups (1958-67, 1968-77, 1978-87, 1988-97, and 1998-2007), stratified by sex. FINDINGS During 50 years of observation (202,417 person-years), 1544 cases of new-onset atrial fibrillation occurred (of whom 723 [47%] were women). Between 1958-67 and 1998-2007, age-adjusted prevalence of atrial fibrillation quadrupled from 20·4 to 96·2 cases per 1000 person-years in men and from 13·7 to 49·4 cases per 1000 person-years in women; age-adjusted incidence increased from 3·7 to 13·4 new cases per 1000 person-years in men and from 2·5 to 8·6 new cases per 1000 person-years in women (ptrend<0·0001 for all comparisons). For atrial fibrillation diagnosed by electrocardiograph (ECG) during routine Framingham examinations, age-adjusted prevalence per 1000 person-years increased (12·6 in 1958-67 to 25·7 in 1998-2007 in men, ptrend=0·0007; 8·1 to 11·8 in women, ptrend=0·009). However, age-adjusted incidence of atrial fibrillation by Framingham Heart Study ECGs did not change significantly with time. Although the prevalence of most risk factors changed over time, their associated hazards for atrial fibrillation changed little. Multivariable-adjusted proportional hazards models revealed a 74% (95% CI 50-86%) decrease in stroke (hazards ratio [HR] 3·77, 95% CI 1·98-7·20 in 1958-1967 compared with 1998-2007; ptrend=0·0001) and a 25% (95% CI -3-46%) decrease in mortality (HR 1·34, 95% CI 0·97-1·86 in 1958-1967 compared with 1998-2007; ptrend=0·003) in 20 years following atrial fibrillation onset. INTERPRETATION Trends of increased incidence and prevalence of atrial fibrillation in the community were probably partly due to enhanced surveillance. Measures are needed to enhance early detection of atrial fibrillation, through increased awareness coupled with targeted screening programmes and risk factor-specific prevention. FUNDING NIH, NHLBI, NINDS, Deutsche Forschungsgemeinschaft.

Simple risk model predicts incidence of atrial fibrillation in a racially and geographically diverse population: the CHARGE-AF consortium

Background Tools for the prediction of atrial fibrillation (AF) may identify high‐risk individuals more likely to benefit from preventive interventions and serve as a benchmark to test novel putative risk factors. Methods and Results Individual‐level data from 3 large cohorts in the United States (Atherosclerosis Risk in Communities [ARIC] study, the Cardiovascular Health Study [CHS], and the Framingham Heart Study [FHS]), including 18 556 men and women aged 46 to 94 years (19% African Americans, 81% whites) were pooled to derive predictive models for AF using clinical variables. Validation of the derived models was performed in 7672 participants from the Age, Gene and Environment—Reykjavik study (AGES) and the Rotterdam Study (RS). The analysis included 1186 incident AF cases in the derivation cohorts and 585 in the validation cohorts. A simple 5‐year predictive model including the variables age, race, height, weight, systolic and diastolic blood pressure, current smoking, use of antihypertensive medication, diabetes, and history of myocardial infarction and heart failure had good discrimination (C‐statistic, 0.765; 95% CI, 0.748 to 0.781). Addition of variables from the electrocardiogram did not improve the overall model discrimination (C‐statistic, 0.767; 95% CI, 0.750 to 0.783; categorical net reclassification improvement, −0.0032; 95% CI, −0.0178 to 0.0113). In the validation cohorts, discrimination was acceptable (AGES C‐statistic, 0.664; 95% CI, 0.632 to 0.697 and RS C‐statistic, 0.705; 95% CI, 0.664 to 0.747) and calibration was adequate. Conclusion A risk model including variables readily available in primary care settings adequately predicted AF in diverse populations from the United States and Europe.

Cardiac Involvement in Patients with Sarcoidosis: Diagnostic and Prognostic Value of Outpatient Testing

BACKGROUND Cardiac sarcoidosis (CS) causes substantial morbidity and sudden death. Early diagnosis and risk stratification are warranted. METHODS Ambulatory patients with sarcoidosis were interviewed to determine whether they experienced palpitations, syncope, or presyncope, and were evaluated with ECG, Holter monitoring, and echocardiography (transthoracic echocardiogram [TTE]). Those with symptoms or abnormal results were studied with cardiac MRI (CMRI) or positron emission tomography (PET) scanning. The diagnosis of CS was based on abnormalities detected by these imaging studies. Patients with CS were referred for risk stratification by electrophysiology study (EPS). RESULTS Among the 62 patients evaluated, the prevalence of CS was 39%. Patients with CS had more cardiac symptoms than those without CS (46% vs 5%, respectively; p < 0.001), and were more likely to have abnormal Holter monitoring findings (50% vs 3%, respectively; p < 0.001) and TTE findings (25% vs 5%, respectively; p = 0.02). The degree of pulmonary impairment did not predict CS. Two of the 17 patients who underwent EPS had abnormal test findings and received implantable cardioverter-defibrillators. No patients died, had ventricular arrhythmias that triggered defibrillator therapy, or had heart failure develop during almost 2 years of follow-up. This diagnostic approach was more sensitive than the established criteria for identifying CS. CONCLUSION CS is common among patients with sarcoidosis. A structured clinical assessment incorporating advanced cardiac imaging with PET scanning or CMRI is more sensitive than the established criteria for the identification of CS. Sarcoidal lesions seen on CMRI or PET scanning do not predict arrhythmias in ambulatory patients with preserved cardiac function, who appear to be at low risk for short-term mortality.

Association Between Familial Atrial Fibrillation and Risk of New-Onset Atrial Fibrillation

CONTEXT Although the heritability of atrial fibrillation (AF) is established, the contribution of familial AF to predicting new-onset AF remains unknown. OBJECTIVE To determine whether familial occurrence of AF is associated with new-onset AF beyond established risk factors. DESIGN, SETTING, AND PARTICIPANTS The Framingham Heart Study, a prospective community-based cohort study started in 1948. Original and Offspring Cohort participants were aged at least 30 years, were free of AF at the baseline examination, and had at least 1 parent or sibling enrolled in the study. The 4421 participants in this analysis (mean age, 54 [SD, 13] years; 54% women) were followed up through December 31, 2007. MAIN OUTCOME MEASURES Incremental predictive value of incorporating different features of familial AF (any familial AF, premature familial AF [onset ≤65 years old], number of affected relatives, and youngest age of onset in a relative) into a risk model for new-onset AF. RESULTS Across 11,971 examinations during the period 1968-2007, 440 participants developed AF. Familial AF occurred among 1185 participants (26.8%) and premature familial AF occurred among 351 participants (7.9%). Atrial fibrillation occurred more frequently among participants with familial AF than without familial AF (unadjusted absolute event rates of 5.8% and 3.1%, respectively). The association was not attenuated by adjustment for AF risk factors (multivariable-adjusted hazard ratio, 1.40; 95% confidence interval [CI], 1.13-1.74) or reported AF-related genetic variants. Among the different features of familial AF examined, premature familial AF was associated with improved discrimination beyond traditional risk factors to the greatest extent (traditional risk factors, C statistic, 0.842 [95% CI, 0.826-0.858]; premature familial AF, C statistic, 0.846 [95% CI, 0.831-0.862]; P = .004). Modest changes in integrated discrimination improvement were observed with premature familial AF (2.1%). Net reclassification improvement (assessed using 8-year risk thresholds of <5%, 5%-10%, and >10%) did not change significantly with premature familial AF (index statistic, 0.011; 95% CI, -0.021 to 0.042; P = .51), although categoryless net reclassification was improved (index statistic, 0.127; 95% CI, 0.064-0.189; P = .009). CONCLUSIONS In this cohort, familial AF was associated with an increased risk of AF that was not attenuated by adjustment for AF risk factors including genetic variants. Assessment of premature familial AF was associated with a very slight increase in predictive accuracy compared with traditional risk factors.

Complex II inhibition by 3-NP causes mitochondrial fragmentation and neuronal cell death via an NMDA- and ROS-dependent pathway.

Mitochondrial respiratory complex II inhibition plays a central role in Huntingtons disease (HD). Remarkably, 3-NP, a complex II inhibitor, recapitulates HD-like symptoms. Furthermore, decreases in mitochondrial fusion or increases in mitochondrial fission have been implicated in neurodegenerative diseases. However, the relationship between mitochondrial energy defects and mitochondrial dynamics has never been explored in detail. In addition, the mechanism of neuronal cell death by complex II inhibition remains unclear. Here, we tested the temporal and spatial relationship between energy decline, impairment of mitochondrial dynamics, and neuronal cell death in response to 3-NP using quantitative fluorescence time-lapse microscopy and cortical neurons. 3-NP caused an immediate drop in ATP. This event corresponded with a mild rise in reactive oxygen species (ROS), but mitochondrial morphology remained unaltered. Unexpectedly, several hours after this initial phase, a second dramatic rise in ROS occurred, associated with profound mitochondrial fission characterized by the conversion of filamentous to punctate mitochondria and neuronal cell death. Glutamate receptor antagonist AP5 abolishes the second peak in ROS, mitochondrial fission, and cell death. Thus, secondary excitotoxicity, mediated by glutamate receptor activation of the NMDA subtype, and consequent oxidative and nitrosative stress cause mitochondrial fission, rather than energy deficits per se. These results improve our understanding of the cellular mechanisms underlying HD pathogenesis.

European Ancestry as a Risk Factor for Atrial Fibrillation in African Americans

Background— Despite a higher burden of standard atrial fibrillation (AF) risk factors, African Americans have a lower risk of AF than whites. It is unknown whether the higher risk is due to genetic or environmental factors. Because African Americans have varying degrees of European ancestry, we sought to test the hypothesis that European ancestry is an independent risk factor for AF. Methods and Results— We studied whites (n=4543) and African Americans (n=822) in the Cardiovascular Health Study (CHS) and whites (n=10 902) and African Americans (n=3517) in the Atherosclerosis Risk in Communities (ARIC) Study (n=3517). Percent European ancestry in African Americans was estimated with 1747 ancestry informative markers from the Illumina custom ITMAT-Broad-CARe array. Among African Americans without baseline AF, 120 of 804 CHS participants and 181 of 3517 ARIC participants developed incident AF. A meta-analysis from the 2 studies revealed that every 10% increase in European ancestry increased the risk of AF by 13% (hazard ratio, 1.13; 95% confidence interval, 1.03 to 1.23; P=0.007). After adjustment for potential confounders, European ancestry remained a predictor of incident AF in each cohort alone, with a combined estimated hazard ratio for each 10% increase in European ancestry of 1.17 (95% confidence interval, 1.07 to 1.29; P=0.001). A second analysis using 3192 ancestry informative markers from a genome-wide Affymetrix 6.0 array in ARIC African Americans yielded similar results. Conclusions— European ancestry predicted risk of incident AF. Our study suggests that investigating genetic variants contributing to differential AF risk in individuals of African versus European ancestry will be informative.