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Background: Spontaneous coronary artery dissection (SCAD) is a cause of acute coronary syndrome that predominantly affects women. Its pathophysiology remains unclear but connective tissue disorders (CTD) and other vasculopathies have been observed in many SCAD patients. A genetic component for SCAD is increasingly appreciated, although few genes have been robustly implicated. We sought to clarify the genetic cause of SCAD using targeted and genome-wide methods in a cohort of sporadic cases to identify both common and rare disease-associated variants. Methods: A cohort of 91 unrelated sporadic SCAD cases was investigated for rare, deleterious variants in genes associated with either SCAD or CTD, while new candidate genes were sought using rare variant collapsing analysis and identification of novel loss-of-function variants in genes intolerant to such variation. Finally, 2 SCAD polygenic risk scores were applied to assess the contribution of common variants. Results: We identified 10 cases with at least one rare, likely disease-causing variant in CTD-associated genes, although only one had a CTD phenotype. No genes were significantly associated with SCAD from genome-wide collapsing analysis, however, enrichment for TGF (transforming growth factor)-β signaling pathway genes was found with analysis of 24 genes harboring novel loss-of-function variants. Both polygenic risk scores demonstrated that sporadic SCAD cases have a significantly elevated genetic SCAD risk compared with controls. Conclusions: SCAD shares some genetic overlap with CTD, even in the absence of any major CTD phenotype. Consistent with a complex genetic architecture, SCAD patients also have a higher burden of common variants than controls.

Background: Truncating variants in filamin C (FLNC) can cause arrhythmogenic cardiomyopathy (ACM) through haploinsufficiency. Noncanonical splice-altering variants may contribute to this phenotype. Objective: The purpose of this study was to investigate the clinical and functional consequences of a recurrent FLNC intronic variant of uncertain significance (VUS), c.970-4A>G. Methods: Clinical data in 9 variant heterozygotes from 4 kindreds were obtained from 5 tertiary health care centers. We used in silico predictors and functional studies with peripheral blood and patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Isolated RNA was studied by reverse transcription polymerase chain reaction. iPSC-CMs were further characterized at baseline and after nonsense-mediated decay (NMD) inhibition, using quantitative polymerase chain reaction (qPCR), RNA-sequencing, and cellular electrophysiology. American College of Medical Genetics and Genomics (ACMG) criteria were used to adjudicate variant pathogenicity. Results: Variant heterozygotes displayed a spectrum of disease phenotypes, spanning from mild ventricular dysfunction with palpitations to severe ventricular arrhythmias requiring device shocks or progressive cardiomyopathy requiring heart transplantation. Consistent with in silico predictors, the c.970-4A>G FLNC variant activated a cryptic splice acceptor site, introducing a 3-bp insertion containing a premature termination codon. NMD inhibition upregulated aberrantly spliced transcripts by qPCR and RNA-sequencing. Patch clamp studies revealed irregular spontaneous action potentials, increased action potential duration, and increased sodium late current in proband-derived iPSC-CMs. These findings fulfilled multiple ACMG criteria for pathogenicity. Conclusion: Clinical, in silico, and functional evidence support the prediction that the intronic c.970-4A>G VUS disrupts splicing and drives ACM, enabling reclassification from VUS to pathogenic.

Instituto de Salud Carlos III (ISCIII), European Regional Development Fund/European Social Fund "A way to make Europe"/" Investing in your future" [PI18/0004, PI20/0320, PT17/0015/0043]; ISCIII; MCIN; Pro-CNIC Foundation; Severo Ochoa Centers of Excellence program [CEX2020-001041-S]; ISCIII [CM20/00101], Frutos F. de, Ochoa JP, Navarro-Peñalver M, Baas A, Bjerre JV, Zorio E, Méndez I, Lorca R, Verdonschot JAJ, García-Granja PE, Bilinska Z, Fatkin D, Fuentes-Cañamero ME, García-Pinilla JM, García-Álvarez MI, Girolami F, Barriales-Villa R, Díez-López C, Lopes LR, Wahbi K, García-Álvarez A, Rodríguez-Sánchez I, Rekondo-Olaetxea J, Rodríguez-Palomares JF, Gallego-Delgado M, Meder B, Kubanek M, Hansen FG, Restrepo-Córdoba MA, Palomino-Doza J, Ruiz-Guerrero L, Sarquella-Brugada G, Perez-Perez AJ, Bermúdez-Jiménez FJ, Ripoll-Vera T, Rasmussen TB, Jansen M, Sabater-Molina M, Elliot PM, Garcia-Pavia P; European Genetic Cardiomyopathies Initiative Investigators

Background: Truncating variants in desmoplakin ( DSP tv) are an important cause of arrhythmogenic cardiomyopathy; however the genetic architecture and genotype-specific risk factors are incompletely understood. We evaluated phenotype, risk factors for ventricular arrhythmias, and underlying genetics of DSP tv cardiomyopathy. Methods: Individuals with DSP tv and any cardiac phenotype, and their gene-positive family members were included from multiple international centers. Clinical data and family history information were collected. Event-free survival from ventricular arrhythmia was assessed. Variant location was compared between cases and controls, and literature review of reported DSP tv performed. Results: There were 98 probands and 72 family members (mean age at diagnosis 43±8 years, 59% women) with a DSP tv, of which 146 were considered clinically affected. Ventricular arrhythmia (sudden cardiac arrest, sustained ventricular tachycardia, appropriate implantable cardioverter defibrillator therapy) occurred in 56 (33%) individuals. DSP tv location and proband status were independent risk factors for ventricular arrhythmia. Further, gene region was important with variants in cases (cohort n=98; Clinvar n=167) more likely to occur in the regions resulting in nonsense mediated decay of both major DSP isoforms, compared with n=124 genome aggregation database control variants (148 [83.6%] versus 29 [16.4%]; P Conclusions: In the largest series of individuals with DSP tv, we demonstrate that variant location is a novel risk factor for ventricular arrhythmia, can inform variant interpretation, and provide critical insights to allow for precision-based clinical management.

Truncating variants in desmoplakin (Individuals withThere were 98 probands and 72 family members (mean age at diagnosis 43±8 years, 59% women) with aIn the largest series of individuals with

Genetic testing is used to optimise the management of inherited cardiovascular disorders that can cause sudden cardiac death. Yet more genotype–phenotype correlation studies from populations not ascertained on clinical symptoms or family history of disease are required to improve understanding of gene penetrance. We performed targeted sequencing of 25 genes used routinely in clinical genetic testing for inherited cardiovascular disorders in a population of 13,131 asymptomatic older individuals (mean age 75 years) enrolled in the ASPREE trial. Participants had no prior history of cardiovascular disease events, dementia or physical disability at enrolment. Variants were classified following ACMG/AMP standards. Sudden and rapid cardiac deaths were clinically adjudicated as ASPREE trial endpoints, and assessed during mean 4.7 years of follow-up. In total, 119 participants had pathogenic/deleterious variants in one of the 25 genes analysed (carrier rate of 1 in 110 or 0.9%). Participants carried variants associated with hypertrophic cardiomyopathy (N = 24), dilated cardiomyopathy (N = 29), arrhythmogenic right-ventricular cardiomyopathy (N = 22), catecholaminergic polymorphic ventricular tachycardia (N = 4), aortopathies (N = 1), and long-QT syndrome (N = 39). Among 119 carriers, two died from presumed sudden/rapid cardiac deaths during follow-up (1.7%); both with pathogenic variants in long-QT syndrome genes (KCNQ1, SCN5A). Among non-carriers, the rate of sudden/rapid cardiac deaths was significantly lower (0.08%, 11/12936, p

The landscape of genetically related cardiac disease continues to evolve. Heritable genetic variants can be a primary cause of familial or sporadic dilated cardiomyopathy (DCM). There is also increasing recognition that genetic variation is an important determinant of susceptibility to acquired causes of DCM. Genetic forms of DCM can show a wide variety of phenotypic manifestations. Identifying patients who are most likely to benefit from genetic testing is paramount. The objective of this review is to highlight the importance of recognising genetic DCM, key genotype-phenotype correlations and the value of genetic testing in clinical management for both the individual and their family. This is likely to become more relevant as management strategies continue to be refined with genotype-specific recommendations and disease-modifying therapies.

Inherited cardiomyopathies are commonly occurring myocardial disorders that are associated with substantial morbidity and mortality. Clinical management strategies have focused on treatment of heart failure and arrhythmic complications in symptomatic patients according to standardized guidelines. Clinicians are now being urged to implement precision medicine, but what does this involve? Advances in understanding of the genetic underpinnings of inherited cardiomyopathies have brought new possibilities for interventions that are tailored to genes, specific variants, or downstream mechanisms. However, the phenotypic variability that can occur with any given pathogenic variant suggests that factors other than single driver gene mutations are often involved. This is propelling a new imperative to elucidate the nuanced ways in which individual combinations of genetic variation, comorbidities, and lifestyle may influence cardiomyopathy phenotypes. Here, Part 3 of a 5-part precision medicine Focus Seminar series reviews the current status and future opportunities for precision medicine in the inherited cardiomyopathies.

In the initial 3 papers in this Focus Seminar series, the fundamentals and key concepts of precision medicine were reviewed, followed by a focus on precision medicine in the context of vascular disease and cardiomyopathy. For the remaining 2 papers, we focus on precision medicine in the context of arrhythmias. Specifically, in this fourth paper we focus on long QT syndrome, Brugada syndrome, and atrial fibrillation. The final (fifth) paper will deal with catecholaminergic polymorphic ventricular tachycardia. These arrhythmias represent a spectrum of disease ranging from common to relatively rare, with very different genetic and environmental causative factors, and with differing clinical manifestations that range from almost no consequences to lethality in childhood or adolescence if untreated. Accordingly, the emerging precision medicine approaches to these arrhythmias vary significantly, but several common themes include increased use of genetic testing, avoidance of triggers, and personalized risk stratification to guide the use of arrhythmia-specific therapies.

The Trans-Omics for Precision Medicine (TOPMed) programme seeks to elucidate the genetic architecture and biology of heart, lung, blood and sleep disorders, with the ultimate goal of improving diagnosis, treatment and prevention of these diseases. The initial phases of the programme focused on whole-genome sequencing of individuals with rich phenotypic data and diverse backgrounds. Here we describe the TOPMed goals and design as well as the available resources and early insights obtained from the sequence data. The resources include a variant browser, a genotype imputation server, and genomic and phenotypic data that are available through dbGaP (Database of Genotypes and Phenotypes)1. In the first 53,831 TOPMed samples, we detected more than 400 million single-nucleotide and insertion or deletion variants after alignment with the reference genome. Additional previously undescribed variants were detected through assembly of unmapped reads and customized analysis in highly variable loci. Among the more than 400 million detected variants, 97% have frequencies of less than 1% and 46% are singletons that are present in only one individual (53% among unrelated individuals). These rare variants provide insights into mutational processes and recent human evolutionary history. The extensive catalogue of genetic variation in TOPMed studies provides unique opportunities for exploring the contributions of rare and noncoding sequence variants to phenotypic variation. Furthermore, combining TOPMed haplotypes with modern imputation methods improves the power and reach of genome-wide association studies to include variants down to a frequency of approximately 0.01%., The goals, resources and design of the NHLBI Trans-Omics for Precision Medicine (TOPMed) programme are described, and analyses of rare variants detected in the first 53,831 samples provide insights into mutational processes and recent human evolutionary history.

Three-dimensional echocardiography (3DE) is the most accurate cardiac ultrasound technique to assess cardiac structure. 3DE has shown close correlation with cardiac magnetic resonance imaging (CMR) in various populations. There is limited data on the accuracy of 3DE in athletes and its value in detecting alterations during follow-up. Indexed left and right ventricular end-diastolic volume (LVEDVi, RVEDVi), end-systolic volume, ejection fraction (LVEF, RVEF) and left ventricular mass (LVMi) were assessed by 3DE and CMR in two-hundred and one competitive endurance athletes (79% male) from the Pro@Heart trial. Sixty-four athletes were assessed at 2 year follow-up. Linear regression and Bland-Altman analyses compared 3DE and CMR at baseline and follow-up. Interquartile analysis evaluated the agreement as cardiac volumes and mass increase. 3DE showed strong correlation with CMR (LVEDVi r = 0.91, LVEF r = 0.85, LVMi r = 0.84, RVEDVi r = 0.84, RVEF r = 0.86 p 0.001). At follow up, the percentage change by 3DE and CMR were similar (∆LVEDVi r = 0.96 bias - 0.3%, ∆LVEF r = 0.94, bias 0.7%, ∆LVMi r = 0.94 bias 0.8%, ∆RVESVi r = 0.93, bias 1.2%, ∆RVEF r = 0.87 bias 0.4%). 3DE underestimated volumes (LVEDVi bias - 18.5 mL/m

Purpose Electrocardiogram (ECG) QRS voltages correlate poorly with left ventricular mass (LVM). Body composition explains some of the QRS voltage variability. The relation between QRS voltages, LVM and body composition in endurance athletes is unknown. Methods Elite endurance athletes from the Pro@Heart trial were evaluated with 12-lead ECG for Cornell and Sokolow-Lyon voltage and product. Cardiac magnetic resonance imaging assessed LVM. Dual energy x-ray absorptiometry assessed fat mass (FM) and lean mass of the trunk and whole body (LBM). The determinants of QRS voltages and LVM were identified by multivariable linear regression. Models combining ECG, demographics, DEXA and exercise capacity to predict LVM were developed. Results In 122 athletes (19 years, 71.3% male) LVM was a determinant of the Sokolow-Lyon voltage and product (beta = 0.334 and 0.477, p < 0.001) but not of the Cornell criteria. FM of the trunk (beta = - 0.186 and - 0.180, p < 0.05) negatively influenced the Cornell voltage and product but not the Sokolow-Lyon criteria. DEXA marginally improved the prediction of LVM by ECG (r = 0.773 vs 0.510, p < 0.001; RMSE = 18.9 +/- 13.8 vs 25.5 +/- 18.7 g, p > 0.05) with LBM as the strongest predictor (beta = 0.664, p < 0.001). DEXA did not improve the prediction of LVM by ECG and demographics combined and LVM was best predicted by including VO(2)max (r = 0.845, RMSE = 15.9 +/- 11.6 g). Conclusion LVM correlates poorly with QRS voltages with adipose tissue as a minor determinant in elite endurance athletes. LBM is the strongest single predictor of LVM but only marginally improves LVM prediction beyond ECG variables. In endurance athletes, LVM is best predicted by combining ECG, demographics and VO(2)max.

Amyloid cardiomyopathy is emerging as an important and under-recognised cause of heart failure and cardiac arrhythmias, especially in older adults. This disorder is characterised by extracellular deposition of amyloid fibrils that form due to misfolding of secreted light chains (AL) or transthyretin protein (ATTR). In ATTR, amyloid aggregates typically result from excessive accumulation of wild-type transthyretin (ATTRwt) or from protein structural defects caused by TTR gene variants (ATTRv). Amyloid fibril deposition may predominantly affect the heart or show multi-system involvement. Previously considered to be rare and inexorably progressive with no specific therapy, there has been enormous recent interest in ATTR cardiomyopathy due to upwardly-revised estimates of disease prevalence together with development of disease-modifying interventions. Because of this, there is a clinical imperative to have a high index of suspicion to identify potential cases and to be aware of contemporary diagnostic methods and treatment options. Genetic testing should be offered to all patients with proven ATTR to access the benefits of new therapies specific to ATTRv and allow predictive testing of family members. With heightened awareness of amyloid cardiomyopathy and expanded use of genetic testing, a substantial rise in the numbers of asymptomatic individuals who are carriers of pathogenic variants is expected, and optimal strategies for monitoring and treatment of these individuals at risk need to be determined. Pre-emptive administration of fibril-modifying therapies provides an unprecedented opportunity for disease prevention and promises to change amyloid cardiomyopathy from being a fatal to a treatable disorder.

Coronary artery disease (CAD) and atrial fibrillation (AF) are two highly prevalent cardiovascular disorders that are associated with substantial morbidity and mortality. Conventional clinical risk factors for these disorders may not be identified prior to mid-adult life when pathophysiological processes are already established. A better understanding of the genetic underpinnings of disease should facilitate early detection of individuals at risk and preventative intervention. Single rare variants of large effect size that are causative for CAD, AF, or predisposing factors such as hypertension or hyperlipidaemia, may give rise to familial forms of disease. However, in most individuals, CAD and AF are complex traits in which combinations of genetic and acquired factors play a role. Common genetic variants that affect disease susceptibility have been identified by genome-wide association studies, but the predictive value of any single variant is limited. To address this issue, polygenic risk scores (PRS), comprised of suites of disease-associated common variants have been devised. In CAD and AF, incorporation of PRS into risk stratification algorithms has provided incremental prognostic information to clinical factors alone. The long-term health and economic benefits of PRS-guided clinical management remain to be determined however, and further evidence-based data are required.

Background: Variants in the SCN5A gene, that encodes the cardiac sodium channel, Nav1.5, are associated with a highly arrhythmogenic form of dilated cardiomyopathy (DCM). Our aim was to review the phenotypes, natural history, functional effects, and treatment outcomes of DCM-associated rare SCN5A variants. Methods: A systematic review of reported DCM-associated rare SCN5A variants was undertaken using PubMed and Embase. Results: Eighteen SCN5A rare variants in 29 families with DCM (173 affected individuals) were identified. Eleven variants had undergone experimental evaluation, with 7 of these resulting in increased sustained current flow during the action potential (eg, increased window current) and at resting membrane potentials (eg, creation of a new gating pore current). These variants were located in transmembrane voltage-sensing domains and had a consistent phenotype characterized by frequent multifocal narrow and broad complex ventricular premature beats (VPB; 72% of affected relatives), ventricular arrhythmias (33%), atrial arrhythmias (32%), sudden cardiac death (13%), and DCM (56%). This VPB-predominant phenotype was not seen with 1 variant that increased late sodium current, or with variants that reduced peak current density or had mixed effects. In the latter groups, affected individuals mainly showed sinus node dysfunction, conduction defects, and atrial arrhythmias, with infrequent VPB and ventricular arrhythmias. DCM did not occur in the absence of arrhythmias for any variant. Twelve studies (23 total patients) reported treatment success in the VPB-predominant cardiomyopathy using sodium channel-blocking drug therapy. Conclusions: SCN5A variants can present with a diverse spectrum of primary arrhythmic features. A majority of DCM-associated variants cause a multifocal VPB-predominant cardiomyopathy that is reversible with sodium channel blocking drug therapy. Early recognition of the distinctive phenotype and prompt genetic testing to identify variant carriers are needed. Our findings have implications for interpretation and management of SCN5A variants found in DCM patients with and without arrhythmias.

IMPORTANCE: Dilated cardiomyopathy (DCM) is frequently caused by genetic factors. Studies identifying deleterious rare variants have predominantly focused on early-onset cases, and little is known about the genetic underpinnings of the growing numbers of patients with DCM who are diagnosed when they are older than 60 years (ie, late-onset DCM). OBJECTIVE: To investigate the prevalence, type, and prognostic impact of disease-associated rare variants in patients with late-onset DCM. DESIGN, SETTING, AND PARTICIPANTS: A population of patients with late-onset DCM who had undergone genetic testing in 7 international tertiary referral centers worldwide were enrolled from March 1990 to August 2020. A positive genotype was defined as the presence of pathogenic or likely pathogenic (P/LP) variants. MAIN OUTCOMES AND MEASURES: The study outcome was all-cause mortality. RESULTS: A total of 184 patients older than 60 years (103 female [56%]; mean [SD] age, 67 [6] years; mean [SD] left ventricular ejection fraction, 32% [10%]) were studied. Sixty-six patients (36%) were carriers of a P/LP variant. Titin-truncating variants were the most prevalent (present in 46 [25%] of the total population and accounting for 46 [69%] of all genotype-positive patients). During a median (interquartile range) follow-up of 42 (10-115) months, 23 patients (13%) died; 17 (25%) of these were carriers of P/LP variants, while 6 patients (5.1%) were genotype-negative. CONCLUSIONS AND RELEVANCE: Late-onset DCM might represent a distinct subgroup characterized by and a high genetic variation burden, largely due to titin-truncating variants. Patients with a positive genetic test had higher mortality than genotype-negative patients. These findings support the extended use of genetic testing also in older patients.

Precision medicine promises to dramatically improve patient outcomes and reduce health care costs through a shift in focus from disease treatment to prevention and individualized therapies. For families with inherited cardiomyopathies, efforts to date have been directed toward discovery and functional characterization of single disease-causing variants. With advances in sequencing, the cataloging of personal genetic variation has been expedited, providing improved insights into the key importance of the genes in which variants occur. These advances have propelled seminal opportunities for successful variant-targeted disease-reversing therapy. New challenges have also emerged-particularly interpretation of the rapidly rising numbers of "variants of unknown significance." For treatments based on patient genotype to be feasible on a wider scale, these obstacles need to be overcome. Here the authors focus on genetics of dilated cardiomyopathy and provide a roadmap for implementing genomic information into future patient management.

Variants in theA systematic review of reported DCM-associated rareEighteen

Aims Dilated cardiomyopathy (DCM) is frequently caused by genetic factors. Studies identifying deleterious rare variants have predominantly focused on early-onset cases, and little is known about the genetic underpinnings of the growing numbers of patients with DCM who are diagnosed after 60 years of age (i.e. late-onset DCM). The aim is to investigate the prevalence, type, and prognostic impact of disease-associated rare variants in late-onset DCM patients. Methods and results We analysed a population of late-onset DCM patients who had undergone genetic testing in seven international tertiary referral centres worldwide. A positive genotype was defined as the presence of ‘pathogenic’ or ‘likely pathogenic’ (P/LP) variants. The study outcome was all-cause mortality. 184 patients over age 60 years (56% females, mean age 67 ± 6 years, mean left ventricular ejection fraction 32 ± 10%) were studied. Sixty-six patients (36%) were carriers of a P/LP variant. Titin truncating variants (TTNtv) were the most prevalent (present in 25% of the total population and accounting for 69% of all genotype-positive patients). During a median follow-up of 42 months (interquartile range: 10–115), 23 patients (13%) died; 17 of these (25%) were carriers of P/LP variants while six patients (5.1%) were genotype-negative (P Conclusions In the largest series worldwide, to date, of patients with late-onset DCM, we found a high prevalence of female sex and a high genetic mutation burden, largely due to TTNtv. Patients with a positive genetic test had higher mortality than genotype-negative patients. These findings support the extended use of genetic testing also in the elderly.

BackgroundTruncating variants in desmoplakin (DSPtv) are an important cause of arrhythmogenic cardiomyopathy (ACM), however the genetic architecture and genotype-specific risk factors are incompletely understood. We evaluated phenotype, risk factors for ventricular arrhythmias, and underlying genetics ofDSPtv cardiomyopathy.MethodsIndividuals withDSPtv and any cardiac phenotype, and their gene-positive family members were included from multiple international centers. Clinical data and family history information were collected. Event-free survival from ventricular arrhythmia was assessed. Variant location was compared between cases and controls, and literature review of reportedDSPtv performed.ResultsThere were 98 probands and 72 family members (mean age at diagnosis 43 ± 18 years, 59% female) with aDSPtv, of which 146 were considered clinically affected. Ventricular arrhythmia (sudden cardiac arrest, sustained ventricular tachycardia, appropriate implantable cardioverter defibrillator therapy) occurred in 56 (33%) individuals.DSPtv location and proband status were independent risk factors for ventricular arrhythmia, while prior risk factors showed no association. Further, gene region was important with variants in cases (cohort n=98, Clinvar n=168) more likely to occur in the regions resulting in nonsense mediated decay of both majorDSPisoforms, compared to n=124 gnomAD control variants (148 [83.6%] versus 29 [16.4%], pConclusionsIn the largest series of individuals withDSPtv, we demonstrate variant location is a novel risk factor for ventricular arrhythmia, can inform variant interpretation, and provide critical insights to allow precision-based clinical management.

Background/Introduction SCAD typically affects women in their fifth or sixth decade with a paucity of cardiovascular risk factors.(1) It is caused by a coronary artery intramural haematoma with or without intimal tear. Resultant luminal occlusion manifests as myocardial ischaemia/infarction or death. There are two published sporadic cases of SCAD who developed iatrogenic aortic dissection with coronary angiography.(2, 3) We are not aware of any SCAD cases with intercurrent or historical spontaneous aortic dissection. There is a published SCAD case with a familial history of aortic dissection, in her mother.(4) None of these cases reported a connective tissue disorder. Methods We searched our database of 338 SCAD cases, recruited via social media or cardiologist referral, for cases with a family history of aortic dissection. SCAD diagnosis was confirmed by review of coronary angiogram images by an expert interventional cardiologist blinded to the genetic analysis. Genomic DNA was extracted from buccal cells collected using a cheek swab or mouthwash sample. Whole genome sequencing was performed using the Illumina HiSeq X Ten platform with 30x coverage. These data are being analysed for rare variants in genes associated with familial aortopathies or connective tissue disorders (e.g. FBN1, COL3A1, TGFbR-1/2, SMAD3), as well as for novel gene associations with aortic dissection and/or SCAD. Results We identified 12 cases with a first- or second-degree relative with aortic dissection. Of these SCAD cases, 11 were female whereas 10 of 12 relatives with aortic dissection were male. In one instance, a maternal uncle, but not the index SCAD case, had Marfan's syndrome. Whole genome sequencing has been performed on the 12 SCAD cases, 2 living relatives with aortic dissection and 2 relatives linking the SCAD and aortic dissection cases. Conclusions Coronary and aortic dissections have serious consequences and in some families there may be a genetic association between the two conditions. Early identification of variant carriers is critical for disease prevention. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): This work was supported in part by grants from the Cardiac Society of Australia and New Zealand, the National Health and Medical Research Council, Australia (APP1161200), the St Vincent's Clinic Foundation, the Catholic Archdiocese of Sydney, Perpetual Philanthropy, NSW Health and SCAD Research Inc. LMC is funded by a University Postgraduate Scholarship through University of NSW and a grant from the Avant Foundation.

Background:HeterozygousTTNtruncating variants cause 10% to 20% of idiopathic dilated cardiomyopathy (DCM). Although variants which disrupt canonical splice signals (ie, invariant dinucleotide of the splice donor site, invariant dinucleotide of the splice acceptor site) at exon-intron junctions are readily recognized asTTNtruncating variants, the effects of other nearby sequence variations on splicing and their contribution to disease is uncertain.Methods:Rare variants of unknown significance located in the splice regions of highly expressedTTNexons from 203 DCM cases, 3329 normal subjects, and clinical variant databases were identified. The effects of these variants on splicing were assessed using an in vitro splice assay.Results:Splice-altering variants of unknown significance were enriched in DCM cases over controls and present in 2% of DCM patients (P=0.002). Application of this method to clinical variant databases demonstrated 20% of similar variants of unknown significance inTTNsplice regions affect splicing. Noncanonical splice-altering variants were most frequently located at position +5 of the donor site (P=4.4×107) and position -3 of the acceptor site (P=0.002). SpliceAI, an emerging in silico prediction tool, had a high positive predictive value (86%–95%) but poor sensitivity (15%–50%) for the detection of splice-altering variants. Alternate exons spliced out of mostTTNtranscripts frequently lacked the consensus base at +5 donor and −3 acceptor positions.Conclusions:Noncanonical splice-altering variants inTTNexplain 1-2% of DCM and offer a 10-20% increase in the diagnostic power ofTTNsequencing in this disease. These data suggest rules that may improve efforts to detect splice-altering variants in other genes and may explain the low percent splicing observed for many alternateTTNexons.

Mechanosensitive channels are integral membrane proteins that sense mechanical stimuli. Like most plasma membrane ion channel proteins they must pass through biosynthetic quality control in the endoplasmic reticulum that results in them reaching their destination at the plasma membrane. Here we show that N-linked glycosylation of two highly conserved asparagine residues in the ‘cap’ region of mechanosensitive Piezo1 channels are necessary for the mature protein to reach the plasma membrane. Both mutation of these asparagines (N2294Q/N2331Q) and treatment with an enzyme that hydrolyses N-linked oligosaccharides (PNGaseF) eliminates the fully glycosylated mature Piezo1 protein. The N-glycans in the cap are a pre-requisite for N-glycosylation in the ‘propeller’ regions, which are present in loops that are essential for mechanotransduction. Importantly, trafficking-defective Piezo1 variants linked to generalized lymphatic dysplasia and bicuspid aortic valve display reduced fully N-glycosylated Piezo1 protein. Thus the N-linked glycosylation status in vitro correlates with efficient membrane trafficking and will aid in determining the functional impact of Piezo1 variants of unknown significance., Li et al. investigates the role of N-linked glycosylation for the function of mechanosensitive ion channel Piezo1. They show that disease-linked loss of function mutations in Piezo1 that are trafficking defective lack N-linked glycosylation.

BACKGROUND: Heterozygous truncating variants in titin (TTNtv) cause 10–20% of idiopathic dilated cardiomyopathy (DCM). Though variants which disrupt canonical splice signals (i.e. GT, AG) at exon-intron junctions are readily recognized as TTNtv, the effects of other nearby sequence variations on splicing and their contribution to disease is uncertain. METHODS: Rare variants of unknown significance (VUS) located in the splice regions of highly expressed TTN exons from 203 DCM cases, 3329 normal subjects, and clinical variant databases were identified. The effects of these variants on splicing were assessed using an in vitro splice assay. RESULTS: Splice-altering VUS were enriched in DCM cases over controls and present in 2% of DCM patients (p=0.002). Application of this method to clinical variant databases demonstrated 20% of similar VUS in TTN splice regions affect splicing. Non-canonical splice-altering variants were most frequently located at position +5 of the donor site (p=4.4e-7) and position −3 of the acceptor site (p=0.002). SpliceAI, an emerging in-silico prediction tool, had a high positive predictive value (86–95%) but poor sensitivity (15–50%) for the detection of splice-altering variants. Alternate exons spliced out of most TTN transcripts frequently lacked the consensus base at +5 donor and −3 acceptor positions. CONCLUSION: Non-canonical splice-altering variants in TTN explain 1–2% of DCM and offer a 10–20% increase in the diagnostic power of TTN sequencing in this disease. These data suggest rules that may improve efforts to detect splice-altering variants in other genes and may explain the low percent splicing observed for many alternate TTN exons.