Variants In Sarcomeric Genes Research Articles

Myocardial DNA damage is responsible for the relationship between genotype and treatment response in patients with dilated cardiomyopathy

Abstract Background Dilated cardiomyopathy (DCM) is one of the leading causes of heart transplantation. Our group and others have previously reported that DNA damage accumulation in myocardial tissue and certain genetic variants such as those in LMNA are associated with treatment response and prognosis (ref 1-5). However, the potential association between myocardial DNA damage and genotype, and their contribution when combined to predicting treatment response, remains unclear. Methods We identified the deleterious variants in cardiomyopathy-related genes by analyzing the whole exome sequencing data from 89 patients with DCM who were recruited from two participating facilities. Immunostaining of γ-H2A.X, a DNA damage marker, was performed on endomyocardial biopsy specimens from the same patients, from which the percentage of nuclei positive for γ-H2A.X signals (%γ-H2A.X) was calculated. Left ventricular reverse remodeling (LVRR) was assessed by transthoracic echocardiography at 1 year after biopsy. We examined the associations among genotype, myocardial DNA damage, and the achievement of LVRR. Results Among the 89 patients with DCM, 11 (12.4%) carried pathogenic or likely pathogenic (P/LP) variants in sarcomere genes such as TTN, and 21 (23.6%) carried P/LP variants in non-sarcomere genes such as LMNA, while the rest had no P/LP variants in cardiomyopathy-related genes (Figure A). Patients with P/LP variants in sarcomere genes had a lower %γ-H2A.X [21.2 (10.7–29.0)% vs. 7.0 (4.3–12.4)%, P = 0.002] (Figure B), and a higher probability to achieve LVRR at 1-year (81.8% vs. 23.8%, P = 0.003) (Figure C) when compared to those with P/LP variants in non-sarcomere genes. The odds ratio for carriers of P/LP variants in sarcomere genes to achieve LVRR was 14.40 (95%CI 2.31–89.94) compared to that for carriers of P/LP variants in non-sarcomere genes. However, this effect was markedly attenuated after adjusting for the proportion of γ-H2A.X-positive nuclei [adjusted odds ratio 6.05 (95%CI 0.86–42.53)] (Table). Conclusions Among patients with DCM, carriers of P/LP variants in sarcomere genes showed less DNA damage and a favorable treatment response, when compared with carriers of P/LP variants in non-sarcomere genes. Our results suggest that myocardial DNA damage was partially responsible for the relationship between genotype and treatment response in patients with DCM.Figure, panels A-C

AFFECT-HCM: quality of life and costs in hypertrophic cardiomyopathy

Abstract Background Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease, characterised by increased wall thickness. Pathogenic DNA variants in sarcomeric genes are identified in about half of HCM patients, enabling pre-symptomatic testing in family members. Since the first description of HCM tremendous progress has been made in the evaluation and management of HCM patients. However, little is known on the impact of HCM on quality of life (QoL) and costs. Purpose The AFFECT-HCM study evaluates the QoL, healthcare and societal costs in HCM patients and genotype-positive phenotype-negative (G+/P-) subjects. Methods The AFFECT-HCM is a multi-centre prospective study including genotyped HCM patients aged 18-80 years and G+/P- subjects. The study cohort is divided into three groups based on phenotype: G+/P- (wall thickness <13 mm), non-obstructive HCM (nHCM, maximal left ventricular outflow tract (LVOT) gradient <30 mmHg) and obstructive HCM (oHCM, LVOT gradient ≥30 mmHg). For QoL, the generic five-domain five-level EQ-5D-5L with the attached visual analogue scale and disease-specific Kansas City Cardiomyopathy Questionnaire are used. Healthcare and societal costs are measured via a bottom-up approach using the cost questionnaires iMCQ and iPCQ and expressed with means (the standard in healthcare cost reporting despite non-normality) in 2023 Euro per patient per year (€ PPPY). QoL and costs are compared between phenotypes. Results Results are summarised in the table. Between November 2022 - December 2023, 506 subjects (mean age 55 years, 39% female) were included in three Dutch hospitals. The study included 84 G+/P-, 307 nHCM and 115 oHCM subjects. Questionnaire response rate was 92%. Compared to G+/P- subjects; HCM patients were older (57 vs 46 yrs), more often male (67% vs 32%) and had more cardiovascular risk factors. Compared to nHCM patients, oHCM patients were more often symptomatic (58% vs 34%), more often in NYHA class III (19% vs 2%) and used more HCM-related medications (79% vs 64%). HCM patients, and particularly oHCM patients, reported decreased QoL with lower QoL-related questionnaire scores (Figure). The utilities (EQ-5D-5L) of HCM patients were lower than G+/P- subjects and the Dutch overall average (0.87±0.17), and for oHCM comparable with another study (0.82±0.18). Costs were higher for HCM patients than G+/P- subjects (€14374 vs €5888 PPPY) and higher in oHCM patients compared to nHCM patients (€19672 vs €12419 PPPY). The leading between-group difference is higher productivity losses in oHCM patients. Conclusion HCM is associated with reduced QoL and increased costs, especially in oHCM patients. The primary cost driver are healthcare costs, but the difference between oHCM and nHCM patients is mainly caused by indirect costs due to productivity losses. These data provide novel insights in the BoD of HCM and can aid in assessing cost-effectiveness analyses of new therapies for HCM in the future.Baseline characteristics and resultsQuality of life-related questionnaires

Epi-Allele: CRISPR-mediated allele-specific epigenetic editing alleviates hypertrophic cardiomyopathy

Abstract Background Hypertrophic cardiomyopathy (HCM) is a prevalent genetic heart disease caused by variants in sarcomere genes like MYH7, which accounts for 40% of cases with 75% being heterozygous. HCM shows incomplete penetrance, where mutant allele expression correlates with severity. Thus, allele-specific suppression is a potential therapy. While allele-specific RNAi or CRISPR/Cas9 showed moderate efficacy, low expression level of MYH7 is associated with the risk of heart failure and dilated cardiomyopathy. We hypothesized CRISPR-based epigenetic editing（dCas9 fused with DNA methylation and histone regulation elements） may potently achieve phenotypic modification without impacting overall gene expression. Objective We investigated allele-specific CRISPR epigenetic editing (Epi-Allele) to selectively suppress mutant Myh6 allele expression without affecting total expression, as a novel HCM therapy in a mouse model. Results We first generated C57R403Q/DBA mice to simulate heterozygous HCM patients. Allele-specific Myh6 gRNAs reduced C57 allele expression and increased DBA expression without impacting total Myh6 expression in primary cardiomyocytes, effects sustained for one year in report cells. HCM mice with Epigenetic editor and allele-specific gRNAs (Epi-Allele) showed reduced left ventricular wall thickness, normalized ECG, and less cardiac fibrosis. Similar therapeutic effects were observed in HCM mice treated by a dual AAV delivery system of Epi-Allele. We further found that Epi-Allele could reverse established disease in the inducible transgene mice. We’ve also seen similar surprising therapeutic effects from Epi-Alleles in patient-derived pluripotent stem cell-induced cardiomyocytes (iPSC-CMs). Conclusion We suggest that Epi-Allele may be a novel therapy for HCM and other dominant diseases where the mutant gene plays a vital role, overcoming the limitations of previous allele-specific suppression strategy.Figure abstract of Epi-AlleleThe universality of Epi-Alleles

Rare Genetic Variants in Young Adults Requiring Pacemaker Implantation

BackgroundGenetic disease has recently emerged as a cause of cardiac conduction disorders (CCDs), but the diagnostic yield of genetic testing and the contribution of the different genes to CCD is still unsettled. ObjectivesThis study sought to determine the diagnostic yield of genetic testing in young adults with CCD of unknown etiology requiring pacemaker implantation. We also studied the prevalence of rare protein-altering variants across individual genes and functional gene groups. MethodsWe performed whole exome sequencing in 150 patients with CCD of unknown etiology who had permanent pacemaker implanted at age ≤60 years at 14 Spanish hospitals. Prevalence of rare protein-altering variants in patients with CCD was compared with a reference population of 115,522 individuals from gnomAD database (control subjects). ResultsAmong 39 prioritized genes, patients with CCD had more rare protein-altering variants than control subjects (OR: 2.39; 95% CI: 1.75-3.33). Significant enrichment of rare variants in patients with CCD was observed in all functional gene groups except in the desmosomal genes group. Rare variants in the nuclear envelope genes group exhibited the strongest association with CCD (OR: 6.77; 95% CI: 3.71-13.87). Of note, rare variants in sarcomeric genes were also enriched (OR: 1.73; 95% CI: 1.05-3.10). An actionable genetic variant was detected in 21 patients (14%), with LMNA being the most frequently involved gene (4.6%). ConclusionsUnrecognized rare genetic variants increase the risk of CCD in young adults with CCD of unknown etiology. Genetic testing should be performed in patients age ≤60 years with CCD of unknown etiology. The role of genetic variants in sarcomeric genes as a cause of CCD should be further investigated.

Phenotypic Spectrum of Subclinical Sarcomere-Related Hypertrophic Cardiomyopathy and Transition to Overt Disease.

Genetic hypertrophic cardiomyopathy (HCM) is classically caused by pathogenic/likely pathogenic variants in sarcomere genes (G+). Currently, HCM is diagnosed if there is unexplained left ventricular (LV) hypertrophy with LV wall thickness ≥15 mm in probands or ≥13 mm in at-risk relatives. Although LV hypertrophy is a key feature, this binary metric does not encompass the full constellation of phenotypic features, particularly in the subclinical stage of the disease. Subtle phenotypic manifestations can be identified in sarcomere variant carriers with normal LV wall thickness, before diagnosis with HCM (G+/LV hypertrophy-; subclinical HCM). We conducted a systematic review to summarize current knowledge about the phenotypic spectrum of subclinical HCM and factors influencing penetrance and expressivity. Although the mechanisms driving the development of LV hypertrophy are yet to be elucidated, activation of profibrotic pathways, impaired relaxation, abnormal Ca2+ signaling, altered myocardial energetics, and microvascular dysfunction have all been identified in subclinical HCM. Progression from subclinical to clinically overt HCM may be more likely if early phenotypic manifestations are present, including ECG abnormalities, longer mitral valve leaflets, lower global E' velocities on Doppler echocardiography, and higher serum N-terminal propeptide of B-type natriuretic peptide. Longitudinal studies of variant carriers are critically needed to improve our understanding of penetrance, characterize the transition to disease, identify risk predictors of phenotypic evolution, and guide the development of novel treatment strategies aimed at influencing disease trajectory.

Impaired Relaxation in Induced Pluripotent Stem Cell-Derived Cardiomyocytes with Pathogenic TNNI3 Mutation of Pediatric Restrictive Cardiomyopathy.

Restrictive cardiomyopathy (RCM) is characterized by impaired diastolic function with preserved ventricular contraction. Several pathogenic variants in sarcomere genes, including TNNI3, are reported to cause Ca2+ hypersensitivity in cardiomyocytes in overexpression models; however, the pathophysiology of induced pluripotent stem cell (iPSC)-derived cardiomyocytes specific to a patient with RCM remains unknown. We established an iPSC line from a pediatric patient with RCM and a heterozygous TNNI3 missense variant, c.508C>T (p.Arg170Trp; R170W). We conducted genome editing via CRISPR/Cas9 technology to establish an isogenic correction line harboring wild type TNNI3 as well as a homozygous TNNI3-R170W. iPSCs were then differentiated to cardiomyocytes to compare their cellular physiological, structural, and transcriptomic features. Cardiomyocytes differentiated from heterozygous and homozygous TNNI3-R170W iPSC lines demonstrated impaired diastolic function in cell motion analyses as compared with that in cardiomyocytes derived from isogenic-corrected iPSCs and 3 independent healthy iPSC lines. The intracellular Ca2+ oscillation and immunocytochemistry of troponin I were not significantly affected in RCM-cardiomyocytes with either heterozygous or homozygous TNNI3-R170W. Electron microscopy showed that the myofibril and mitochondrial structures appeared to be unaffected. RNA sequencing revealed that pathways associated with cardiac muscle development and contraction, extracellular matrix-receptor interaction, and transforming growth factor-β were altered in RCM-iPSC-derived cardiomyocytes. Patient-specific iPSC-derived cardiomyocytes could effectively represent the diastolic dysfunction of RCM. Myofibril structures including troponin I remained unaffected in the monolayer culture system, although gene expression profiles associated with cardiac muscle functions were altered.

Abstract 12408: Response to Mavacamten by Sarcomere Gene Mutation Status in EXPLORER-HCM

Background: Mavacamten is a small molecule inhibitor of cardiac myosin that was developed based on insights into the molecular basis of hypertrophic cardiomyopathy (HCM). In the phase 3 EXPLORER-HCM trial (NCT03470545), patients showed consistent benefit in the primary endpoint with mavacamten treatment vs placebo while subgroup analysis of patients with pathogenic or likely pathogenic variants in a broad panel of HCM-related genes, revealed a slightly more favorable response. However, it is unknown how patients specifically with sarcomere gene variants responded. Aims: To assess the effect of HCM-specific sarcomere gene variants on response to mavacamten. Methods: Sequencing using a 60 gene panel (Invitae) was optional in EXPLORER-HCM. In this exploratory analysis, responses to mavacamten vs placebo for the primary, secondary, and exploratory endpoints were analysed. Patients were grouped based on sarcomere gene variant status (positive for pathogenic/likely pathogenic/variants of uncertain significance [SARC+], negative [SARC–]) or no sequencing). Analyses were adjusted for clinically relevant variables. Results: Of 190/251 patients sequenced, 73 were SARC+ (mavacamten, n = 33; placebo, n = 40), 117 were SARC– (mavacamten, n = 57; placebo, n = 60) and 61 had no panel sequencing (mavacamten, n = 33; placebo, n = 28). Mavacamten treatment showed a favorable response for the primary endpoint vs placebo, for SARC+ (odds ratio [OR], 4.43 [95% CI, 1.56-12.58]), and for SARC– (OR, 2.52 [95% CI, 0.99-6.42]) ( Figure ). Improvements with mavacamten vs placebo were observed in both SARC+ and SARC– subgroups for change from baseline to week 30 in post-exercise left ventricular outflow tract gradient, and peak oxygen consumption, and in New York Heart Association class. Conclusions: In this exploratory subgroup analysis, mavacamten treatment benefit was observed both in patients with and without sarcomere gene variants.

Genetic variants, pathophysiological pathways, and oral anticoagulation in patients with hypertrophic cardiomyopathy and atrial fibrillation.

Atrial fibrillation (AF) is commonly prevalent in patients with hypertrophic cardiomyopathy (HCM). However, whether the prevalence and incidence of AF are different between genotype-positive vs. genotype-negative patients with HCM remains controversial. Recent evidence has indicated that AF is often the first presentation of genetic HCM patients in the absence of a cardiomyopathy phenotype, implying the importance of genetic testing in this population with early-onset AF. However, the association of the identified sarcomere gene variants with HCM occurrence in the future remains unclear. How the identification of these cardiomyopathy gene variants should influence the use of anticoagulation therapy for a patient with early-onset AF is still undefined. In this review, we sought to assess the genetic variants, pathophysiological pathways, and oral anticoagulation in patients with HCM and AF.

Long QTc in hypertrophic cardiomyopathy: A consequence of structural myocardial damage or a distinct genetic disease?

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease, characterized by the presence of unexplained left ventricular hypertrophy. This condition is often associated with electrocardiographic abnormalities including QTc prolongation occurring in 13% of patients. The main explanation for prolonged QTc in HCM is myocardial hypertrophy and the related structural damage. However, other mechanisms, including long QT syndrome (LQTS) genes mutations, may be involved. In the present study we explored the hypothesis of a distinct genetic basis underlying QTc prolongation in HCM by investigating the potential co-inheritance of pathogenic gene variants associated with LQTS and HCM. For this purpose, starting from a cohort of 150 HCM patients carrying pathogenic variants in sarcomere genes, we selected 25 patients carrying a QTc prolongation unexplained by any other cause. The QTc was considered prolonged if greater than 450 ms in males and greater than 470 ms in females. The NGS analysis was performed with Illumina TrueSight Cardio panel genes on Illumina MiniSeq platform. We identified pathogenic/likely pathogenic variants in the KCNQ1 in two patients (c.1781G > A, p. Arg594Gln; c.532G > A, p. Ala178Thr) (8%). Variants of uncertain significance were identified in SCN5A, KCNJ5, AKAP9 and ANK2 in four patients (16%). Although the results are limited by the small number of patients included in the study, they highlight a minor contribution of LQTS genes for QTc prolongation in HCM patients. The screening for ion channel genes mutations may be considered in HCM patients with prolonged QTc unexplained by any other cause. This in-depth molecular diagnosis may contribute to improve risk stratification and treatment planning.

1064 LONG QTC IN HCM: A CONSEQUENCE OF MYOCARDIAL HYPERTROPHY OR A DISTINCT GENETIC DISEASE?

Abstract Hypertrophic cardiomyopathy (HCM) is an autosomal dominant condition, characterized by the presence of unexplained left ventricular hypertrophy. This condition is usually associated with electrocardiographic abnormalities including QTc prolongation reported in the 13% of HCM patients. The main explanation for QTc prolongation in HCM is myocardial hypertrophy and the related structural damage. However, mechanisms other than myocardial hypertrophy, including long QT syndrome (LQTS) gene mutations, may also be involved. The addictive effect of 2 disease-causing mutations has been already reported in other pathological conditions. In the present study we investigated the possible co-inheritance of pathogenic variants associated with both LQTS and HCM, exploring the hypothesis of a distinct genetic basis underlying QTc prolongation in HCM. For this purpose, we considered a cohort of 150 HCM patients carrying pathogenic variants in sarcomeric genes. Out of them we selected 25 patients carrying a QTc prolongation not explained by any other cause (drugs, etc). The QTc was considered prolonged if greater than 450 ms in males and greater than 470 ms in females. NGS analysis was performed with Illumina TrueSight Cardio panel genes on Illumina MiniSeq platform to evaluate the presence of pathogenetic variants in LQTS related genes. We identified pathogenic/likely pathogenic variants in LQTS related gene KCNQ1 (c.1781G>A, p. Arg594Gln; c.532G>A, p. Ala178Thr) in two patients (8%) and uncertain significant variants in SCN5A, KCNJ5, AKAP9 and ANK2 in four patients (16%). Although the results of our study are limited by the small number of patients included in the analysis, they highlight a minor contribution of LQTS genes in HCM patients with a QTc prolongation. The screening for ion channel gene mutations should be considered in HCM patients with QTc prolongation, not explained by any other cause. This strategy may be important for risk stratification and treatment planning.

Contemporary Therapies and Future Directions in the Management of Hypertrophic Cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is a genetic disorder caused by pathogenic variants in sarcomeric genes, leading to left ventricular hypertrophy and complex phenotypic heterogeneity. While HCM is the most common inherited cardiomyopathy, pharmacological treatment options have previously been limited and were predominantly directed towards symptom control owing to left ventricular outflow obstruction. These therapies, including beta blockers, calcium channel blockers, and disopyramide, have not been shown to affect the natural history of the disease, which is of particular concern for younger patients who have an increased lifetime risk of experiencing arrhythmias, heart failure, and sudden cardiac death. Increased knowledge of the genetic mechanisms underlying this disease in recent years has led to the development of targeted, potentially disease-modifying therapies for both obstructive and nonobstructive phenotypes that may help to prevent or ameliorate left ventricular hypertrophy. In this review article, we will define the etiology and clinical phenotypes of HCM, summarize the conventional therapies for obstructive HCM, discuss the emerging targeted therapies as well as novel invasive approaches for obstructive HCM, describe the therapeutic advances for nonobstructive HCM, and outline the future directions for the treatment of HCM.

Atomic force microscopy identifies the alteration of rheological properties of the cardiac fibroblasts in idiopathic restrictive cardiomyopathy.

Restrictive cardiomyopathy (RCM) is a rare disease characterized by increased ventricular stiffness and preserved ventricular contraction. Various sarcomere gene variants are known to cause RCM; however, more than a half of patients do not harbor such pathogenic variants. We recently demonstrated that cardiac fibroblasts (CFs) play important roles in inhibiting the diastolic function of cardiomyocytes via humoral factors and direct cell–cell contact regardless of sarcomere gene mutations. However, the mechanical properties of CFs that are crucial for intercellular communication and the cardiomyocyte microenvironment remain less understood. In this study, we evaluated the rheological properties of CFs derived from pediatric patients with RCM and healthy control CFs via atomic force microscopy. Then, we estimated the cellular modulus scale factor related to the cell stiffness, fluidity, and Newtonian viscosity of single cells based on the single power-law rheology model and analyzed the comprehensive gene expression profiles via RNA-sequencing. RCM-derived CFs showed significantly higher stiffness and viscosity and lower fluidity compared to healthy control CFs. Furthermore, RNA-sequencing revealed that the signaling pathways associated with cytoskeleton elements were affected in RCM CFs; specifically, cytoskeletal actin-associated genes (ACTN1, ACTA2, and PALLD) were highly expressed in RCM CFs, whereas several tubulin genes (TUBB3, TUBB, TUBA1C, and TUBA1B) were down-regulated. These results implies that the signaling pathways associated with cytoskeletal elements alter the rheological properties of RCM CFs, particularly those related to CF–cardiomyocyte interactions, thereby leading to diastolic cardiac dysfunction in RCM.

Abstract P2112: Human Genetics And Engineered Heart Tissues Link Frail MYH7 Alleles To Delayed Maturation And Ventricular Noncompaction

Background: Up to 1% of humans are born with a congenital heart defect. Among those defects is a condition known as left ventricular noncompaction (LVNC), which is defined as the ratio of trabeculated myocardium to compact myocardium exceeding 2.3:1. The process of compaction occurs when the layer of compact cardiomyocytes (CMs) proliferates, while CMs in the trabecular layer quiesce. This differential expansion of the CM layers reduces the trabecular invaginations into the cardiac lumen. Deficient compact CM proliferation or excessive trabecular CM proliferation converge on a similar presentation, collectively referred to as noncompaction. Family and population genetics studies have implicated deleterious variants in sarcomere genes as highly correlated with LVNC (PMID: 18506004, PMID: 3350056); specifically, MYH7 truncations and missense variants that fall within the first 600 amino acids of the beta myosin heavy chain head region. Hypothesis: Reduced contractility in certain MYH7 head domain missense or truncating variants disrupts cardiomyocyte terminal maturation, leading to excessive trabeculation. Results: We identified individuals and families with MYH7 Lys234Asn and Arg243His. Variant carriers had LVNC often in the setting of dilated cardiomyopathy, similar to what has been described with MYH7 truncations. We engineered MYH7 truncations in human induced pluripotent stem cells (hiPSCs) which were differentiated into engineered heart tissues (EHTs) to model the developing heart. In EHTs with MYH7 truncations contractility was reduced by 50%, EHT size increased by 17%, and CM proliferation increased by 40% in EHTs heterozygous for MYH7 truncations (N=6 each). Conclusions and Future Directions: Our observations of impaired differentiation, reduced contractility, and decreased compaction are consistent with LVNC phenotypes. We propose a general model where diminished contractility delays sarcomere maturation, extending the proliferation time of trabecular cardiomyocytes and resulting in excessive trabeculae.

Signal-to-Noise Analysis Can Inform the Likelihood That Incidentally Identified Variants in Sarcomeric Genes Are Associated with Pediatric Cardiomyopathy.

Background: Hypertrophic cardiomyopathy (HCM) is the most common heritable cardiomyopathy and can predispose individuals to sudden death. Most pediatric HCM patients host a known pathogenic variant in a sarcomeric gene. With the increase in exome sequencing (ES) in clinical settings, incidental variants in HCM-associated genes are being identified more frequently. Diagnostic interpretation of incidental variants is crucial to enhance clinical patient management. We sought to use amino acid-level signal-to-noise (S:N) analysis to establish pathogenic hotspots in sarcomeric HCM-associated genes as well as to refine the 2015 American College of Medical Genetics (ACMG) criteria to predict incidental variant pathogenicity. Methods and Results: Incidental variants in HCM genes (MYBPC3, MYH7, MYL2, MYL3, ACTC1, TPM1, TNNT2, TNNI3, and TNNC1) were obtained from a clinical ES referral database (Baylor Genetics) and compared to rare population variants (gnomAD) and variants from HCM literature cohort studies. A subset of the ES cohort was clinically evaluated at Texas Children’s Hospital. We compared the frequency of ES and HCM variants at specific amino acid locations in coding regions to rare variants (MAF < 0.0001) in gnomAD. S:N ratios were calculated at the gene- and amino acid-level to identify pathogenic hotspots. ES cohort variants were re-classified using ACMG criteria with S:N analysis as a correlate for PM1 criteria, which reduced the burden of variants of uncertain significance. In the clinical validation cohort, the majority of probands with cardiomyopathy or family history hosted likely pathogenic or pathogenic variants. Conclusions: Incidental variants in HCM-associated genes were common among clinical ES referrals, although the majority were not disease-associated. Leveraging amino acid-level S:N as a clinical tool may improve the diagnostic discriminatory ability of ACMG criteria by identifying pathogenic hotspots.

Abstract 11792: Low Penetrance Sarcomere Variants Indicate an Additive Genetic Risk Model in Hypertrophic Cardiomyopathy

Introduction: Genetic hypertrophic cardiomyopathy (HCM) is an autosomal dominant inherited condition primarily due to pathogenic variants in sarcomere genes, often with marked clinical variability. We hypothesized that this variability may, in part, be due to additive effects from low penetrance sarcomere variants that would otherwise be dismissed due to high population prevalence. Methods: Low-penetrance HCM-associated sarcomere gene variants were identified by meeting a threshold for enrichment in HCM (ascertained from the Sarcomeric Human Cardiomyopathy Registry, SHaRe) versus the general population (ascertained from the Genome Aggregation Database, gnomAD), defined by an odds ratio (OR) &gt;5, and a population prevalence greater than the most common autosomal dominant pathogenic HCM variant, MYBPC3 R502W (4x10 -5 ). Clinical variables and time-event analyses were performed from SHaRe . Results: A total of 507 unique sarcomere gene variants were present in 6384 individuals with genetic testing. Ten putative low-penetrance variants were identified in the genes MYBPC3 (N=2), TNNT2 (N=1), TNNI3 (N=2), and MYH7 (N=5) with a combined OR of 12.7 (range 5.8 - 28.4). These variants had a population prevalence of 4.02x10 -5 to 3.5x10 -4 . Family members of low-penetrance variant carriers were less likely to have HCM (35/171, 20%) than those of MYBPC3 R502W carriers (44/113, 39%, p&lt;0.005). Age of diagnosis was older in patients with isolated low-penetrance variants than those with pathogenic variants (42 ± 19 vs 37 ± 18, p=0.005). Composite adverse events were less likely in patients with isolated low-penetrance variants than typical pathogenic sarcomere variants, but the risk was additive with both present (see Figure). Conclusions: A subset of low-penetrance sarcomere gene variants are tolerated in the general population at higher than expected proportions for HCM and may exert an additive pathogenic effect. These findings support an oligogenic risk model of HCM.

Cohort of patients with hypertrophic cardiomyopathy and alpha tropomyosin 1 variants followed up at a national reference center

Abstract Background Hypertrophic cardiomyopathy (HCM), the most common inherited cardiac condition, is mainly caused by pathogenic variants in sarcomeric genes. Alpha tropomyosin gene (TPM1) account for a small percentage (1–5%) of HCM cases with ∼20 relevant variants described so far related to this condition. However, TPM1–hypertrophic cardiomyopathy is thought to be associated with high rates of heart failure and sudden death (SD). Purpose To describe the phenotype and genotype of a cohort of adult and pediatric patients with HCM and variants in TPM1 followed up in an inherited cardiovascular disease program of a national reference center. Methods Patients with HCM and TPM1 variants potentially related to the phenotype were retrospectively identified. Genetic test was performed by next generation sequencing panels or clinical exome. Clinical data, any need of intervention (obstruction relief, device implantation, heart transplant) and major adverse cardiovascular events were collected from medical records. We performed co-segregation studies whenever possible. Predictive models in order to support the possible pathogenicity of the variants were also applied. Results We identified 13 individuals (54% females) from 11 families with HCM and variants in TPM1. 12 patients had phenotype and one was a carrier. 5 out of 12 patients (42%) were diagnosed before the age of 12 years, all with severe phenotype. The most frequent pattern was asymmetric septal hypertrophy, with a mean thickness of the septum of 22 mm (range 14–37). 4 cases were obstructive, of which 3 required surgical myectomy. 4 patients required an implanted cardiac defibrillator (ICD), all in childhood. One was in secondary prevention after an aborted SD in a 12-year-old girl. 3 appropriate therapies were recorded in 2 patients during follow-up. A girl underwent heart transplantation at the age of 12 because of angina at rest. At last evaluation 67% were symptomatic, with 3 patients in functional class II and 5 patients in functional class III-IV/IV. 8 missense variants in TPM1 were identified in the 11 families (table 1). All variants are described in Clinvar as variants of unknown significance (VUS). They appear at a very low frequency (&amp;lt;0.01%) or are absent in general population and predictive models of protein structure and functionality (PreditProtein) indicate an impact on the structure of the protein, supporting their possible pathogenicity. Figure 1 shows a diagram of the variants position within TPM1 gen. Cossegregation data and the presence of the same variant in non_related families allowed us to reclassify 4 variants as “likely pathogenic”. Conclusion This study provides cosegregation data and “in silico” analysis of the potential functional impact of several TPM1 variants, supporting their pathogenicity. In our cohort, HCM related to TMP1 variants is associated with high penetrance (92%), early onset and poor clinical course in childhood and youth. Funding Acknowledgement Type of funding sources: None. Figure 1

Novel Morphological Features on CMR for the Prediction of Pathogenic Sarcomere Gene Variants in Subjects Without Hypertrophic Cardiomyopathy.

Background: Carriers of pathogenic DNA variants (G+) causing hypertrophic cardiomyopathy (HCM) can be identified by genetic testing. Several abnormalities have been brought forth as pre-clinical expressions of HCM, some of which can be identified by cardiovascular magnetic resonance (CMR). In this study, we assessed morphological differences between G+/left ventricular hypertrophy-negative (LVH-) subjects and healthy controls and examined whether CMR-derived variables are useful for the prediction of sarcomere gene variants.Methods: We studied 57 G+ subjects with a maximal wall thickness (MWT) < 13 mm, and compared them to 40 healthy controls matched for age and sex on a group level. Subjects underwent CMR including morphological, volumetric and function assessment. Logistic regression analysis was performed for the determination of predictive CMR characteristics, by which a scoring system for G+ status was constructed.Results: G+/LVH- subjects were subject to alterations in the myocardial architecture, resulting in a thinner posterior wall thickness (PWT), higher interventricular septal wall/PWT ratio and MWT/PWT ratio. Prominent hook-shaped configurations of the anterobasal segment were only observed in this group. A model consisting of the anterobasal hook, multiple myocardial crypts, right ventricular/left ventricular ratio, MWT/PWT ratio, and MWT/left ventricular mass ratio predicted G+ status with an area under the curve of 0.92 [0.87–0.97]. A score of ≥3 was present only in G+ subjects, identifying 56% of the G+/LVH- population.Conclusion: A score system incorporating CMR-derived variables correctly identified 56% of G+ subjects. Our results provide further insights into the wide phenotypic spectrum of G+/LVH- subjects and demonstrate the utility of several novel morphological features. If genetic testing for some reason cannot be performed, CMR and our purposed score system can be used to detect possible G+ carriers and to aid planning of the control intervals.

Reduced Systolic Function and Not Genetic Variants Determine Outcome in Pediatric and Adult Left Ventricular Noncompaction Cardiomyopathy.

Background: Left ventricular noncompaction cardiomyopathy (LVNC CMP) is a genetic cardiomyopathy. Genotype-phenotype correlation and clinical outcome of genetic variants in pediatric and adult LVNC CMP patients are still unclear.Methods: The retrospective multicenter study was conducted in unrelated index patients with LVNC CMP, diagnosed between the years 1987 and 2017, and all available family members. All index patients underwent next-generation sequencing for genetic variants in 174 target genes using the Illumina TruSight Cardio Sequencing Panel. Major adverse cardiac events (MACE) included mechanical circulatory support, heart transplantation, survivor of cardiac death, and/or all-cause death as combined endpoint.Results: Study population included 149 LVNC CMP patients with a median age of 27.8 (9.2–44.8) years at diagnosis; 58% of them were symptomatic, 18% suffered from non-sustained and sustained arrhythmias, and 17% had an implantable cardioverter defibrillator (ICD) implanted. 55/137 patients (40%) were ≤ 18 years at diagnosis.A total of 134 variants were identified in 87/113 (77%) index patients. 93 variants were classified as variant of unknown significance (VUS), 24 as likely pathogenic and 15 as pathogenic. The genetic yield of (likely) pathogenic variants was 35/113 (31%) index patients. Variants occurred most frequently in MYH7 (n=19), TTN (n = 10) and MYBPC3 (n = 8). Altogether, sarcomere gene variants constituted 42.5% (n = 57) of all variants. The presence or absence of (likely) pathogenic variants or variants in specific genes did not allow risk stratification for MACE.Reduced left ventricular (LV) systolic function and increased left ventricular end-diastolic diameter (LVEDD) were risk factors for event-free survival in the Kaplan-Meier analysis. Through multivariate analysis we identified reduced LV systolic function as the main risk factor for MACE. Patients with reduced LV systolic function were at a 4.6-fold higher risk for MACE.Conclusions: Genetic variants did not predict the risk of developing a MACE, neither in the pediatric nor in the adult cohort. Multivariate analysis emphasized reduced LV systolic function as the main independent factor that is elevating the risk for MACE. Genetic screening is useful for cascade screening to identify family members at risk for developing LVNC CMP.

Alpha-protein kinase 3 (ALPK3) truncating variants are a cause of autosomal dominant hypertrophic cardiomyopathy.

AimsThe aim of this study was to determine the frequency of heterozygous truncating ALPK3 variants (ALPK3tv) in patients with hypertrophic cardiomyopathy (HCM) and confirm their pathogenicity using burden testing in independent cohorts and family co-segregation studies.Methods and results In a discovery cohort of 770 index patients with HCM, 12 (1.56%) were heterozygous for ALPK3tv [odds ratio(OR) 16.11, 95% confidence interval (CI) 7.94–30.02, P = 8.05e−11] compared to the Genome Aggregation Database (gnomAD) population. In a validation cohort of 2047 HCM probands, 32 (1.56%) carried heterozygous ALPK3tv (OR 16.17, 95% CI 10.31–24.87, P < 2.2e−16, compared to gnomAD). Combined logarithm of odds score in seven families with ALPK3tv was 2.99. In comparison with a cohort of genotyped patients with HCM (n = 1679) with and without pathogenic sarcomere gene variants (SP+ and SP−), ALPK3tv carriers had a higher prevalence of apical/concentric patterns of hypertrophy (60%, P < 0.001) and of a short PR interval (10%, P = 0.009). Age at diagnosis and maximum left ventricular wall thickness were similar to SP− and left ventricular systolic impairment (6%) and non-sustained ventricular tachycardia (31%) at baseline similar to SP+. After 5.3 ± 5.7 years, 4 (9%) patients with ALPK3tv died of heart failure or had cardiac transplantation (log-rank P = 0.012 vs. SP− and P = 0.425 vs. SP+). Imaging and histopathology showed extensive myocardial fibrosis and myocyte vacuolation.Conclusions Heterozygous ALPK3tv are pathogenic and segregate with a characteristic HCM phenotype.

Genetic evaluation of cardiomyopathies in Qatar identifies enrichment of pathogenic sarcomere gene variants and possible founder disease mutations in the Arabs.

BackgroundHypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are serious inherited heart diseases with various causative mutations identified. The full spectrum of causative mutations remains to be discovered, especially in understudied populations.MethodsHere, we established the DOHA Registry and Biobank for cardiomyopathies in Qatar, followed by sequencing of 174 genes on 51 HCM and 53 DCM patients, and 31 relatives.ResultsIn HCM, the analysis of 25 HCM‐associated genes showed that 20% of HCM cases had putative pathogenic variants for cardiomyopathy, mainly in sarcomere genes. Additional 49% of HCM cases had variants of uncertain significance, while 31% of HCM cases had likely benign variant(s) or had no variants identified within the analyzed HCM genes. In DCM, 56 putative DCM genes were analyzed. Eight percent of DCM cases had putative pathogenic variants for DCM, in the TTN gene while 70% of cases had variants of uncertain significance, in the analyzed DCM genes, that will need further pathogenicity assessment. Moreover, 22% of DCM cases remain unexplained, by having likely benign variant(s) or having no variants detected in any of the analyzed DCM genes.ConclusionWe identified or replicated at least four recurrent variants among cardiomyopathy patients, which could be founder disease mutations in the Arabic population, including a frameshift variant (c.1371_1381dupTATCCAGTTAT) of unknown significance in the FKTN gene which seems to cause DCM in homozygosity, and HCM in heterozygosity. In vivo and/or in vitro functional validation need to be pursued in order to assess the pathogenicity of the identified variants.