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Aims: Interest in targeted screening programmes for atrial fibrillation (AF) has increased, yet the role of genetics in identifying patients at highest risk of developing AF is unclear., Methods and Results: A total of 36,662 subjects without prior AF were analyzed from four TIMI trials. Subjects were divided into quintiles using a validated polygenic risk score (PRS) for AF. Clinical risk for AF was calculated using the CHARGE-AF model. Kaplan-Meier event rates, adjusted hazard ratios (HRs), C-indices, and net reclassification improvement were used to determine if the addition of the PRS improved prediction compared with clinical risk and N-terminal pro-B-type natriuretic peptide (NT-proBNP). Over 2.3 years, 1018 new AF cases developed. AF PRS predicted a significant risk gradient for AF with a 40% increased risk per 1-SD increase in PRS [HR: 1.40 (1.32-1.49); P < 0.001]. Those with high AF PRS (top 20%) were more than two-fold more likely to develop AF [HR 2.45 (1.99-3.03), P < 0.001] compared with low PRS (bottom 20%). Furthermore, PRS provided an additional gradient of risk stratification on top of the CHARGE-AF clinical risk score, ranging from a 3-year incidence of 1.3% in patients with low clinical and genetic risk to 8.7% in patients with high clinical and genetic risk. The subgroup of patients with high clinical risk, high PRS, and elevated NT-proBNP had an AF risk of 16.7% over 3 years. The C-index with the CHARGE-AF clinical risk score alone was 0.65, which improved to 0.67 (P < 0.001) with the addition of NT-proBNP, and increased further to 0.70 (P < 0.001) with the addition of the PRS., Conclusion: In patients with cardiovascular conditions, AF PRS is a strong independent predictor of incident AF that provides complementary predictive value when added to a validated clinical risk score and NT-proBNP., Competing Interests: Conflict of interest: N.A.M. reports grant support from the National Institutes of Health and involvement in clinical trials with Amgen, Pfizer, Novartis, AstraZeneca, and Ionis without personal fees, payments, or increase in salary. A.C.G., F.K.K., and G.M.M. report no disclosures. C.R. is supported by a grant from Bayer AG to the Broad Institute focused on the development of therapeutics for cardiovascular disease. P.J. reports research support from Abbott Laboratories, Amgen, Inc., AstraZeneca, LP, Daiichi-Sankyo, Inc., Eisai, Inc., GlaxoSmithKline, Merck & Co., Inc., Regeneron Pharmaceuticals, Inc., Roche Diagnostics Corporation, Siemens Healthineers, Takeda Global Research and Development Center, and Waters Technologies Corporation, and consulting fees from Roche Diagnostics Corporation. D.D.B. is supported by Harvard Catalyst KL2/CMeRIT (NIH/NCATS UL 1TR002541) and has received research grant support to his institution from AstraZeneca and Pfizer and consulting fees from AstraZeneca. D.L.B. reports grants from AstraZeneca, during the conduct of the study; grants from Amarin, AstraZeneca, Bristol-Myers Squibb, Garmin, Owkin, HLS Therapeutics, Eisai, Ethicon, Medtronic, 89Bio, sanofi aventis, Contego Medical, The Medicines Company, Roche, Pfizer, Forest Laboratories/AstraZeneca, Stasys, Ischemix, Amgen, Lilly, Chiesi, Ironwood, Merck, Abbott, Regeneron, Idorsia, Faraday Pharmaceuticals, Javelin, Reid Hoffman Foundation, Moderna, Beren, Aker Biomarine, Recardio, Acesion Pharma, Synaptic, Fractyl, Afimmune, Ferring Pharmaceuticals, Lexicon; other from FlowCo, Clinical Cardiology, VA, Takeda, Endotronix, Vascular Solutions, and Svelte, grants and other from PLx Pharma, Novartis, NirvaMed, MyoKardia/BMS, Janssen, Novo Nordisk, Cardax, and Boston Scientific, PhaseBio, Novo Nordisk, Cereno Scientific, CellProthera; personal fees from Duke Clinical Research Institute, Oakstone CME, High Enroll, Bristol-Myers Squibb, Mayo Clinic, Arnold and Porter law firm, Piper Sandler, Cowen and Company, Assistance Publique-Hôpitaux de Paris, Rutgers University, Wiley, AngioWave, K2P, Canadian Medical and Surgical Knowledge Translation Research Group, Journal of the American College of Cardiology, TobeSoft, Bayer, MJH Life Sciences, Level Ex, Population Health Research Institute, Belvoir Publications, Slack Publications, WebMD, Elsevier, Harvard Clinical Research Institute (now Baim Institute for Clinical Research), HMP Global, Cleveland Clinic, Mount Sinai School of Medicine, Medtelligence/ReachMD, CSL Behring; personal fees from from DRS. LINQ, non-financial support, and other from American College of Cardiology; other from Medscape Cardiology, Philips, Regado Biosciences, Boston VA Research Institute, St. Jude Medical (now Abbott), Biotronik, CSI; personal fees and non-financial support from Society of Cardiovascular Patient Care; non-financial support from American Heart Association; grants, personal fees, and other from Boehringer Ingelheim, outside the submitted work. M.P.B. discloses grant support from Amgen, AstraZeneca, Bayer, and Sanofi and consulting fees from Amgen, AstraZeneca, Bayer, and Sanofi. C.P.C. reports research grants from Amgen, Boehringer Ingelheim (BI), Bristol-Myers Squibb (BMS), Daiichi-Sankyo, Janssen, Merck, Novo Nordisk, and Pfizer. Consulting fees from Aegerion, Alnylam, Amarin, Amgen, Applied Therapeutics, Ascendia, BI, BMS, Corvidia, Eli Lilly, HLS Therapeutics, Innovent, Janssen, Kowa, Merck, Pfizer, Rhoshan, and Sanofi. R.P.G. reports grants from Amgen and Daiichi-Sankyo, during the conduct of the study; personal fees from Akcea, GlaxoSmithKline, Janssen, Lexicon, American College of Cardiology, Bristol-Myers Squibb, CVS Caremark, Pfizer, Servier, outside the submitted work; grants and personal fees from Amarin, Daiichi-Sankyo, Merck, Amgen; and Institutional research grant to the TIMI Study Group at Brigham and Women’s Hospital for research he is not directly involved in from Abbott, Amgen, Aralez, AstraZeneca, Bayer HealthCare Pharmaceuticals, Inc., BRAHMS, Daiichi-Sankyo, Eisai, GlaxoSmithKline, Intarcia, Janssen, MedImmune, Merck, Novartis, Pfizer, Poxel, Quark Pharmaceuticals, Roche, Takeda, The Medicines Company, and Zora Biosciences. M.L.O. reports institutional research grants from Amgen, Janssen, The Medicines Company, Eisai, GlaxoSmithKline, and Astra Zeneca. I.R. received personal fees from AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Concenter BioPharma, and Silkim, Eli Lilly, Merck Sharp & Dohme, Novo Nordisk, Orgenesis, Pfizer, Sanofi, SmartZyme Innovation, Panaxia, FutuRx, Insuline Medical, Medial EarlySign, CameraEyes, Exscopia, Dermal Biomics, Johnson & Johnson, Novartis, Teva, GlucoMe, and DarioHealth. B.M.S. reports research grants from AstraZeneca, Eisai, Novartis, and Merck and consulting fees from AstraZeneca, Biogen Idec, Boehringer Ingelheim, Covance, Dr Reddy’s Laboratories, Eisai, Elsevier Practice Update Cardiology, GlaxoSmithKline, Lexicon, Merck, Novo Nordisk, Sanofi, and St Jude’s Medical; and has equity in Health [at] Scale. E.B. reports research grants through the Brigham and Women’s Hospital from Astra Zeneca, Daiichi-Sankyo, Merck, and Novartis. Consultancies with Amgen, Cardurion, MyoKardia, NovoNordisk, Boehringer Ingelheim/Lilly, IMMEDIATE, and Verve. Uncompensated consultancies and lectures with The Medicines Company. D.A.M. reports grants to Brigham and Women’s Hospital from Abbott Laboratories, AstraZeneca, BRAHMS, Daiichi-Sankyo, Eisai, GlaxoSmithKline, Medicines Company, Merck, Novartis, Pfizer, Quark Pharmaceuticals, Roche Diagnostics, Takeda, and Zora Biosciences. He has received consulting fees from Aralez, AstraZeneca, Bayer Pharma, InCarda, Novartis, and Roche Diagnostics. P.T.E. receives sponsored research support from Bayer AG and IBM Health, and he has consulted for Bayer AG, Novartis, MyoKardia, and Quest Diagnostics. S.A.L. receives sponsored research support from Bristol-Myers Squibb/Pfizer, Bayer AG, Boehringer Ingelheim, Fitbit, and IBM and has consulted for Bristol-Myers Squibb/Pfizer, Bayer AG, and Blackstone Life Sciences. Dr. Lubitz is supported by NIH grants R01HL139731, R01HL157635 and American Heart Association 18SFRN34250007. C.T.R. Honoraria; Modest; Bristol-Myers Squib, Pfizer, Portola, Honoraria; Significant; Bayer, Boehringer Ingelheim, Daiichi-Sankyo, Janssen, Research Grant; Modest; Daiichi-Sankyo, MedImmune, National Institute of Health, Research Grant; Significant; Boehringer Ingelheim. M.S.S.: Other; Modest; Anthos Therapeutics, AstraZeneca, Bristol-Myers Squibb, CVS Caremark, DalCor, IFM Therapeutics, Intarcia, Medicines Company, MedImmune, Merck, Other; Significant; Amgen, Research Grant; Significant; Amgen, AstraZeneca, Bayer, Daiichi-Sankyo, Eisai; Intarcia, Medicines Company, MedImmune, Merck, Novartis, Pfizer, Quark., (© The Author(s) 2022. Published by Oxford University Press on behalf of European Society of Cardiology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: To assess the genetic architecture of hypertrophic cardiomyopathy (HCM) in patients of predominantly Chinese ancestry., Methods: We sequenced HCM disease genes in Singaporean patients (n=224) and Singaporean controls (n=3634), compared findings with additional populations and White HCM cohorts (n=6179), and performed in vitro functional studies., Results: Singaporean HCM patients had significantly fewer confidently interpreted HCM disease variants (pathogenic/likely pathogenic: 18%, P <0.0001) but an excess of variants of uncertain significance (24%, P <0.0001), as compared to Whites (pathogenic/likely pathogenic: 31%, excess of variants of uncertain significance: 7%). Two missense variants in thin filament encoding genes were commonly seen in Singaporean HCM (TNNI3:p.R79C, disease allele frequency [AF]=0.018; TNNT2:p.R286H, disease AF=0.022) and are enriched in Singaporean HCM when compared with Asian controls (TNNI3:p.R79C, Singaporean controls AF=0.0055, P =0.0057, genome aggregation database-East Asian AF=0.0062, P =0.0086; TNNT2:p.R286H, Singaporean controls AF=0.0017, P <0.0001, genome aggregation database-East Asian AF=0.0009, P <0.0001). Both these variants have conflicting annotations in ClinVar and are of low penetrance (TNNI3:p.R79C, 0.7%; TNNT2:p.R286H, 2.7%) but are predicted to be deleterious by computational tools. In population controls, TNNI3:p.R79C carriers had significantly thicker left ventricular walls compared with noncarriers while its etiological fraction is limited (0.70 [95% CI, 0.35-0.86]) and thus TNNI3:p.R79C is considered variant of uncertain significance. Mutant TNNT2:p.R286H iPSC-CMs (induced pluripotent stem cells derived cardiomyocytes) show hypercontractility, increased metabolic requirements, and cellular hypertrophy and the etiological fraction (0.93 [95% CI, 0.83-0.97]) support the likely pathogenicity of TNNT2:p.R286H., Conclusions: As compared with Whites, Chinese HCM patients commonly have low penetrance risk alleles in TNNT2 or TNNI3 but exhibit few clinically actionable HCM variants overall. This highlights the need for greater study of HCM genetics in non-White populations.

Background: Hypertrophic cardiomyopathy (HCM) is caused by pathogenic variants in sarcomere protein genes that evoke hypercontractility, poor relaxation, and increased energy consumption by the heart and increased patient risks for arrhythmias and heart failure. Recent studies show that pathogenic missense variants in myosin, the molecular motor of the sarcomere, are clustered in residues that participate in dynamic conformational states of sarcomere proteins. We hypothesized that these conformations are essential to adapt contractile output for energy conservation and that pathophysiology of HCM results from destabilization of these conformations., Methods: We assayed myosin ATP binding to define the proportion of myosins in the super relaxed state (SRX) conformation or the disordered relaxed state (DRX) conformation in healthy rodent and human hearts, at baseline and in response to reduced hemodynamic demands of hibernation or pathogenic HCM variants. To determine the relationships between myosin conformations, sarcomere function, and cell biology, we assessed contractility, relaxation, and cardiomyocyte morphology and metabolism, with and without an allosteric modulator of myosin ATPase activity. We then tested whether the positions of myosin variants of unknown clinical significance that were identified in patients with HCM, predicted functional consequences and associations with heart failure and arrhythmias., Results: Myosins undergo physiological shifts between the SRX conformation that maximizes energy conservation and the DRX conformation that enables cross-bridge formation with greater ATP consumption. Systemic hemodynamic requirements, pharmacological modulators of myosin, and pathogenic myosin missense mutations influenced the proportions of these conformations. Hibernation increased the proportion of myosins in the SRX conformation, whereas pathogenic variants destabilized these and increased the proportion of myosins in the DRX conformation, which enhanced cardiomyocyte contractility, but impaired relaxation and evoked hypertrophic remodeling with increased energetic stress. Using structural locations to stratify variants of unknown clinical significance, we showed that the variants that destabilized myosin conformations were associated with higher rates of heart failure and arrhythmias in patients with HCM., Conclusions: Myosin conformations establish work-energy equipoise that is essential for life-long cellular homeostasis and heart function. Destabilization of myosin energy-conserving states promotes contractile abnormalities, morphological and metabolic remodeling, and adverse clinical outcomes in patients with HCM. Therapeutic restabilization corrects cellular contractile and metabolic phenotypes and may limit these adverse clinical outcomes in patients with HCM.

Rationale: Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) in combination with CRISPR/Cas9 genome editing provide unparalleled opportunities to study cardiac biology and disease. However, sarcomeres, the fundamental units of myocyte contraction, are immature and nonlinear in hiPSC-CMs, which technically challenge accurate functional interrogation of contractile parameters in beating cells. Furthermore, existing analysis methods are relatively low-throughput, indirectly assess contractility, or only assess well-aligned sarcomeres found in mature cardiac tissues., Objective: We aimed to develop an analysis platform that directly, rapidly, and automatically tracks sarcomeres in beating cardiomyocytes. The platform should assess sarcomere content, contraction and relaxation parameters, and beat rate., Methods and Results: We developed SarcTrack, a MatLab software that monitors fluorescently tagged sarcomeres in hiPSC-CMs. The algorithm determines sarcomere content, sarcomere length, and returns rates of sarcomere contraction and relaxation. By rapid measurement of hundreds of sarcomeres in each hiPSC-CM, SarcTrack provides large data sets for robust statistical analyses of multiple contractile parameters. We validated SarcTrack by analyzing drug-treated hiPSC-CMs, confirming the contractility effects of compounds that directly activate (CK-1827452) or inhibit (MYK-461) myosin molecules or indirectly alter contractility (verapamil and propranolol). SarcTrack analysis of hiPSC-CMs carrying a heterozygous truncation variant in the myosin-binding protein C ( MYBPC3) gene, which causes hypertrophic cardiomyopathy, recapitulated seminal disease phenotypes including cardiac hypercontractility and diminished relaxation, abnormalities that normalized with MYK-461 treatment., Conclusions: SarcTrack provides a direct and efficient method to quantitatively assess sarcomere function. By improving existing contractility analysis methods and overcoming technical challenges associated with functional evaluation of hiPSC-CMs, SarcTrack enhances translational prospects for sarcomere-regulating therapeutics and accelerates interrogation of human cardiac genetic variants.

The mechanisms by which truncating mutations in MYBPC3 (encoding cardiac myosin-binding protein C; cMyBPC) or myosin missense mutations cause hypercontractility and poor relaxation in hypertrophic cardiomyopathy (HCM) are incompletely understood. Using genetic and biochemical approaches, we explored how depletion of cMyBPC altered sarcomere function. We demonstrated that stepwise loss of cMyBPC resulted in reciprocal augmentation of myosin contractility. Direct attenuation of myosin function, via a damaging missense variant (F764L) that causes dilated cardiomyopathy (DCM), normalized the increased contractility from cMyBPC depletion. Depletion of cMyBPC also altered dynamic myosin conformations during relaxation, enhancing the myosin state that enables ATP hydrolysis and thin filament interactions while reducing the super relaxed conformation associated with energy conservation. MYK-461, a pharmacologic inhibitor of myosin ATPase, rescued relaxation deficits and restored normal contractility in mouse and human cardiomyocytes with MYBPC3 mutations. These data define dosage-dependent effects of cMyBPC on myosin that occur across the cardiac cycle as the pathophysiologic mechanisms by which MYBPC3 truncations cause HCM. Therapeutic strategies to attenuate cMyBPC activity may rescue depressed cardiac contractility in patients with DCM, whereas inhibiting myosin by MYK-461 should benefit the substantial proportion of patients with HCM with MYBPC3 mutations., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Sarcomere cardiomyopathies are genetic diseases that perturb contractile function and lead to hypertrophic or dilated myocardial remodeling. Identification of preclinical mutation carriers has yielded insights into the earliest biomechanical defects that link pathogenic variants to cardiac dysfunction. Understanding this early molecular pathophysiology can illuminate modifiable pathways to reduce the emergence of overt cardiomyopathy and curb adverse outcomes. Here, the authors review current understandings of how human hypertrophic cardiomyopathy- and hypertrophic dilated cardiomyopathy-linked mutations disrupt the normal structure and function of the sarcomere., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

BackgroundTo evaluate a whole-body rapid imaging technique to calculate neonatal lean body mass and percentage adiposity using 3.0 Tesla chemical shift magnetic resonance imaging (MRI).MethodsA 2-Point Dixon MRI technique was used to calculate whole-body fat and water images in term (n=10) and preterm (n=15) infants.ResultsChemical shift images were obtained in 42 s. MRI calculated whole-body mass correlated closely with measured body weight (R 2 =0.87; P<0.001). Scan-rescan analysis demonstrated a 95% limit of agreement of 1.3% adiposity. Preterm infants were born at a median of 25.7 weeks' gestation with birth weight 840 g. At term-corrected age, former preterm infants were lighter than term-born controls, 2,519 vs. 3,094 g regressing out age and group as covariates (P=0.005). However, this was not because of reduced percentage adiposity 26% vs. 24% (P=0.28). At term-corrected age, former preterm infants had significantly reduced lean body mass compared with that of term-born controls 1,935 vs. 2,416 g (P=0.002).ConclusionRapid whole-body imaging for assessment of lean body mass and adiposity in term and preterm infants is feasible, accurate, and repeatable. Deficits in whole-body mass in former preterm infants at term-corrected age are due to reductions in lean body mass not due to differences in adiposity.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent a powerful cellular platform for illuminating mechanisms of human cardiovascular disease and for pharmacological screening. Recent advances in CRISPR/Cas9-mediated genome editing technology underlie this profound utility. We have generated hiPSC-CMs harboring fluorescently-tagged sarcomeric proteins, which provide a tool to non-invasively study human sarcomere function and dysfunction. In this unit, we illustrate methods for conducting high-efficiency, small molecule-mediated differentiation of hiPSCs into cardiomyocytes, and for performing non-invasive contractile analysis through direct sarcomere tracking of GFP-sarcomere reporter hiPSC-CMs. We believe that this type of analysis can overcome sensitivity problems found in other forms of contractile assays involving hiPSC-CMs by directly measuring contractility at the fundamental contractile unit of the hiPSC-CM, the sarcomere. © 2018 by John Wiley & Sons, Inc., (Copyright © 2018 John Wiley & Sons, Inc.)