iPSC-Based Modeling of Variable Clinical Presentation in Hypertrophic Cardiomyopathy.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease and a frequent cause of heart failure and sudden cardiac death. Our understanding of the genetic bases and pathogenic mechanisms underlying HCM has improved significantly in the recent past, but the combined effect of various pathogenic gene variants and the influence of genetic modifiers in disease manifestation are very poorly understood. Here, we set out to investigate genotype-phenotype relationships in 2 siblings with an extensive family history of HCM, both carrying a pathogenic truncating variant in the MYBPC3 gene (p.Lys600Asnfs*2), but who exhibited highly divergent clinical manifestations. METHODS: We used a combination of induced pluripotent stem cell (iPSC)-based disease modeling and CRISPR (clustered regularly interspersed short palindromic repeats)/Cas9 (CRISPR-associated protein 9)-mediated genome editing to generate patient-specific cardiomyocytes (iPSC-CMs) and isogenic controls lacking the pathogenic MYBPC3 variant. RESULTS: Mutant iPSC-CMs developed impaired mitochondrial bioenergetics, which was dependent on the presence of the mutation. Moreover, we could detect altered excitation-contraction coupling in iPSC-CMs from the severely affected individual. The pathogenic MYBPC3 variant was found to be necessary, but not sufficient, to induce iPSC-CM hyperexcitability, suggesting the presence of additional genetic modifiers. Whole-exome sequencing of the mutant carriers identified a variant of unknown significance in the MYH7 gene (p.Ile1927Phe) uniquely present in the individual with severe HCM. We finally assessed the pathogenicity of this variant of unknown significance by functionally evaluating iPSC-CMs after editing the variant. CONCLUSIONS: Our results indicate that the p.Ile1927Phe variant of unknown significance in MYH7 can be considered as a modifier of HCM expressivity when found in combination with truncating variants in MYBPC3. Overall, our studies show that iPSC-based modeling of clinically discordant subjects provides a unique platform to functionally assess the effect of genetic modifiers.

Outcomes of Patients With Catecholaminergic Polymorphic Ventricular Tachycardia Treated With ß-Blockers.

Importance: Patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) may experience life-threatening arrhythmic events (LTAEs) despite ß-blocker treatment. Further complicating management, the role of implantable cardioverter defibrillator (ICD) in CPVT is debated. Objective: To investigate the long-term outcomes of patients with RYR2 CPVT treated with ß-blockers only and the cost to benefit ratio of ICD. Design, Settings, and Participants: This prospective cohort study conducted from January 1988 to October 2020 with a mean (SD) follow-up of 9.4 (7.5) years included patients who were referred to the Molecular Cardiology Clinics of ICS Maugeri Hospital, Pavia, Italy. Participants included consecutive patients with CPVT who were carriers of a pathogenic or likely pathogenic RYR2 variant with long-term clinical follow-up. Exposures: Treatment with selective and nonselective ß-blocker only and ICD implant when indicated. Main Outcome and Measures: The main outcome was the occurrence of the first LTAE while taking a ß-blocker. LTAE was defined as a composite of 3 hard end points: sudden cardiac death, aborted cardiac arrest, and hemodynamically nontolerated ventricular tachycardia. Results: The cohort included 216 patients with RYR2 CPVT (121 of 216 female [55%], median [IQR] age 14, [9-30] years). During a mean (SD) follow-up of 9.4 (7.5) years taking ß-blockers only, 28 of 216 patients (13%) experienced an LTAE (annual rate, 1.9%; 95% CI, 1.3-2.7). In multivariable analysis, experiencing either an LTAE (hazard ratio [HR], 3.3; 95% CI, 1.2-8.9; P = .02) or syncope before diagnosis (HR, 4.5; 95% CI, 1.8-11.1; P = .001) and carrying a C-terminal domain variant (HR, 18.1; 95% CI, 4.1-80.8; P < .001) were associated with an increased LTAE risk during ß-blocker therapy only. The risk of LTAE among those taking selective ß-blockers vs nadolol was increased 6-fold (HR, 5.8; 95% CI, 2.1-16.3; P = .001). Conversely, no significant difference was present between propranolol and nadolol (HR, 1.8; 95% CI, 0.4-7.3; P = .44). An ICD was implanted in 79 of 216 patients (37%) who were followed up for a mean (SD) of 8.6 (6.3) years. At the occurrence of LTAE, ICD carriers were more likely to survive (18 of 18 [100%]) than non-ICD carriers (6 of 10 [60%]; P = .01). Conclusions and Relevance: In this cohort study, selective ß-blockers were associated with a higher risk of LTAE as compared with nadolol. Independently from treatment, LTAE and syncope before diagnosis and C-terminal domain variants identified patients at higher risk of ß-blocker failure, and the ICD was associated with reduced mortality in high-risk patients with CPVT.

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

AIMS: The 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.

Association of Left Ventricular Systolic Dysfunction Among Carriers of Truncating Variants in Filamin C With Frequent Ventricular Arrhythmia and End-stage Heart Failure.

Importance: Truncating variants in the gene encoding filamin C (FLNCtv) are associated with arrhythmogenic and dilated cardiomyopathies with a reportedly high risk of ventricular arrhythmia. Objective: To determine the frequency of and risk factors associated with adverse events among FLNCtv carriers compared with individuals carrying TTN truncating variants (TTNtv). Design, Setting, and Participants: This cohort study recruited 167 consecutive FLNCtv carriers and a control cohort of 244 patients with TTNtv matched for left ventricular ejection fraction (LVEF) from 19 European cardiomyopathy referral units between 1990 and 2018. Data analyses were conducted between June and October, 2020. Main Outcomes and Measures: The primary end point was a composite of malignant ventricular arrhythmia (MVA) (sudden cardiac death, aborted sudden cardiac death, appropriate implantable cardioverter-defibrillator shock, and sustained ventricular tachycardia) and end-stage heart failure (heart transplant or mortality associated with end-stage heart failure). The secondary end point comprised MVA events only. Results: In total, 167 patients with FLNCtv were studied (55 probands [33%]; 89 men [53%]; mean [SD] age at baseline evaluation, 43 [18] years). For a median follow-up of 20 months (interquartile range, 7-60 months), 29 patients (17.4%) reached the primary end point (19 patients with MVA and 10 patients with end-stage heart failure). Eight (44%) arrhythmic events occurred among individuals with baseline mild to moderate left ventricular systolic dysfunction (LVSD) (LVEF = 36%-49%). Univariable risk factors associated with the primary end point included proband status, LVEF decrement per 10%, ventricular ectopy (≥500 in 24 hours) and myocardial fibrosis detected on cardiac magnetic resonance imaging. The LVEF decrement (hazard ratio [HR] per 10%, 1.83 [95% CI, 1.30-2.57]; P < .001) and proband status (HR, 3.18 [95% CI, 1.12-9.04]; P = .03) remained independent risk factors on multivariable analysis (excluding myocardial fibrosis and ventricular ectopy owing to case censoring). There was no difference in freedom from MVA between FLNCtv carriers with mild to moderate or severe (LVEF ≤35%) LVSD (HR, 1.29 [95% CI, 0.45-3.72]; P = .64). Carriers of FLNCtv with impaired LVEF at baseline evaluation (n = 69) had reduced freedom from MVA compared with 244 TTNtv carriers with similar baseline LVEF (for mild to moderate LVSD: HR, 16.41 [95% CI, 3.45-78.11]; P < .001; for severe LVSD: HR, 2.47 [95% CI, 1.04-5.87]; P = .03). Conclusions and Relevance: The high frequency of MVA among patients with FLNCtv with mild to moderate LVSD suggests that higher LVEF values than those currently recommended should be considered for prophylactic implantable cardioverter-defibrillator therapy in FLNCtv carriers.

Utilidad clínica del estudio genético en pacientes con miocardiopatía dilatada / Clinical utility of genetic testing in patients with dilated cardiomyopathy

Introducción y objetivos: La miocardiopatía dilatada (MCD) es la causa más frecuente de trasplante cardiaco. Se considera que es familiar hasta en el 50% de los casos. Nuestro objetivo es describir los resultados genéticos obtenidos en una cohorte de pacientes con MCD, de los cuales una elevada proporción había acabado en trasplante cardiaco.MétodosSe incluyeron pacientes con MCD a los que se realizó next-generation sequencing (NGS, «secuenciación de nueva generación») de al menos 80 genes relacionados con la enfermedad. Se analizaron retrospectivamente los datos clínicos de los pacientes, la historia familiar y los resultados del estudio genético. En los casos en los que fue posible, se realizó una evaluación de sus familiares de primer grado.ResultadosFueron evaluados 87 pacientes con MCD y 308 familiares de 70 familias distintas. La prevalencia clínica de enfermedad familiar fue del 37% (32 pacientes) y el 44% (38 pacientes) habían precisado un trasplante cardiaco. En 43 pacientes (49%) se encontró al menos una variante relevante, en 25 pacientes (29%) se identificaron variantes de significado incierto y en 19 pacientes (22%) el estudio fue negativo. La mayoría de las mutaciones se encontraron en genes sarcoméricos y la rentabilidad del estudio fue mayor en los pacientes con MCD familiar.ConclusionesEl estudio genético NGS en nuestra población de pacientes con MCD tuvo una elevada rentabilidad, alcanzando el 69% en los casos familiares. El espectro mutacional fue heterogéneo y con frecuencia la identificación de la etiología específica de la enfermedad aportó información pronóstica. (AU)

Introduction and objectives: Dilated cardiomyopathy (DCM) is the most frequent cause of heart transplantation. The prevalence of familial disease can reach 50%. Our objective was to describe the genetic basis of DCM in a cohort with a high proportion of transplanted patients.MethodsWe included patients with DCM and genetic testing performed using next-generation sequencing (NGS) that included at least 80 genes. Clinical data, family history and genetic results were retrospectively analysed. When possible, assessment of first-degree relatives was carried out.ResultsEighty-seven DCM patients and 308 relatives from 70 families were evaluated. Clinical prevalence of familial disease was 37% (32 patients). Forty-four percent of patients (38 patients) had required heart transplantation. A relevant variant was found in 43 patients (49%), 25 patients (29%) carried variants of unknown significance and in 19 patients (22%) the study was negative. Most genetic variants were found in sarcomeric genes and the yield of genetic testing was higher in patients with familial DCM.ConclusionsThe yield of genetic testing in our DCM cohort was high, reaching 69% in familial cases. Mutational spectrum was heterogeneous and the identification of the specific aetiology of the disease often provided prognostic information. (AU)

Risk predictors in a Spanish cohort with cardiac laminopathies. The REDLAMINA registry.

INTRODUCTION AND OBJECTIVES: According to sudden cardiac death guidelines, an implantable cardioverter-defibrillator (ICD) should be considered in patients with LMNA-related dilated cardiomyopathy (DCM) and ≥ 2 risk factors: male sex, left ventricular ejection fraction (LVEF) <45%, nonsustained ventricular tachycardia (NSVT), and nonmissense genetic variants. In this study we aimed to describe the clinical characteristics of carriers of LMNA genetic variants among individuals from a Spanish cardiac-laminopathies cohort (REDLAMINA registry) and to assess previously reported risk criteria. METHODS: The relationship between risk factors and cardiovascular events was evaluated in a cohort of 140 carriers (age ≥ 16 years) of pathogenic LMNA variants (54 probands, 86 relatives). We considered: a) major arrhythmic events (MAE) if there was appropriate ICD discharge or sudden cardiac death; b) heart failure death if there was heart transplant or death due to heart failure. RESULTS: We identified 11 novel and 21 previously reported LMNA-related DCM variants. LVEF <45% (P=.001) and NSVT (P <.001) were related to MAE, but not sex or type of genetic variant. The only factor independently related to heart failure death was LVEF <45% (P <.001). CONCLUSIONS: In the REDLAMINA registry cohort, the only predictors independently associated with MAE were NSVT and LVEF <45%. Therefore, female carriers of missense variants with either NSVT or LVEF <45% should not be considered a low-risk group. It is important to individualize risk stratification in carriers of LMNA missense variants, because not all have the same prognosis.

Clinical utility of genetic testing in patients with dilated cardiomyopathy. / Utilidad clínica del estudio genético en pacientes con miocardiopatía dilatada.

INTRODUCTION AND OBJECTIVES: Dilated cardiomyopathy (DCM) is the most frequent cause of heart transplantation. The prevalence of familial disease can reach 50%. Our objective was to describe the genetic basis of DCM in a cohort with a high proportion of transplanted patients. METHODS: We included patients with DCM and genetic testing performed using next-generation sequencing (NGS) that included at least 80 genes. Clinical data, family history and genetic results were retrospectively analysed. When possible, assessment of first-degree relatives was carried out. RESULTS: Eighty-seven DCM patients and 308 relatives from 70 families were evaluated. Clinical prevalence of familial disease was 37% (32 patients). Forty-four percent of patients (38 patients) had required heart transplantation. A relevant variant was found in 43 patients (49%), 25 patients (29%) carried variants of unknown significance and in 19 patients (22%) the study was negative. Most genetic variants were found in sarcomeric genes and the yield of genetic testing was higher in patients with familial DCM. CONCLUSIONS: The yield of genetic testing in our DCM cohort was high, reaching 69% in familial cases. Mutational spectrum was heterogeneous and the identification of the specific aetiology of the disease often provided prognostic information.

The p.(Cys150Tyr) variant in CSRP3 is associated with late-onset hypertrophic cardiomyopathy in heterozygous individuals.

INTRODUCTION AND OBJECTIVES: Up to 50% of patients with hypertrophic cardiomyopathy (HCM) show no disease-causing variants in genetic studies. Mutations in CSRP3 have been associated with HCM, but evidence supporting pathogenicity is inconclusive. In this study, we describe an HCM cohort with a missense variant in CSRP3 (p.Cys150Tyr) with supporting evidence for pathogenicity and a description of the associated phenotype. METHODS: CSRP3 was sequenced in 6456 index cases with a diagnosis of HCM and in 5012 probands with other cardiomyopathies. In addition, 3372 index cases with hereditary cardiovascular disorders other than cardiomyopathies (mainly channelopathies and aortopathies) were used as controls. RESULTS: The p.(Cys150Tyr) variant was identified in 11 unrelated individuals of the 6456 HCM probands, and it was not identified in patients with other cardiomyopathies (p < 0.0001) or in our control population (p < 0.0001). Ten of the index cases were heterozygous and one was homozygous. Homozygous had a more severe phenotype. Family screening identified 17 other carriers. Wild-type individuals showed no signs of disease. The mean age at diagnosis of affected individuals was 55 ±â€¯13 years, and the mean left ventricular wall thickness was 18 ±â€¯3 mm. The variant showed highly age-dependent penetrance. After a mean follow-up of 11 (±8) years, no adverse events were reported in any of the HCM patients. CONCLUSIONS: The p.(Cys150Tyr) variant in CSRP3 causes late-onset and low risk form of hypertrophic cardiomyopathy in heterozygous carriers.

Reduction in Filamin C transcript is associated with arrhythmogenic cardiomyopathy in Ashkenazi Jews.

BACKGROUND: Filamin C is a cytoskeletal protein expressed in cardiac cells. Nonsense variations in the filamin C gene (FLNC) were associated with dilated and arrhythmogenic cardiomyopathies. METHODS AND RESULTS: We identified an intronic variation in FLNC gene (c.3791-1G > C) in three unrelated Ashkenazi Jewish families with variable expression of arrhythmia and cardiomyopathy. cDNA was prepared from a mutation carrier's cultured skin fibroblasts. Quantitative PCR demonstrated a reduction in total FLNC transcript, and no other FLNC splice variants were found. Single-nucleotide polymorphism (SNP) analysis revealed heterozygous variations in the genomic DNA that were not expressed in the messenger RNA. Immunohistochemical analysis of cardiac sections detected a normal distribution of filamin C protein in the heart ventricles. CONCLUSION: The transcript that included the FLNC variant was degraded. Haploinsufficiency in filamin C underlies arrhythmogenic cardiomyopathy with variable symptoms.

Prognostic implications of pathogenic truncating variants in the TTN gene.

INTRODUCTION AND OBJECTIVES: TTN gene truncating variants (TTNtv) are a frequent cause of dilated cardiomyopathy (DCM). However, there are discrepant data on the associated prognosis. Our objectives were to describe the prevalence of TTNtv in our cohort and to compare the clinical course with that described in the literature. METHODS: We included patients with DCM and genetic testing performed using next-generation sequencing. Through a systematic literature research, we collected information about carriers and affected relatives with TTNtv. We compared the cumulative percentage of affected carriers and the survival free of cardiovascular death. RESULTS: One hundred and ten DCM patients were evaluated. A total of 13 TTNtv distributed in 14 probands were identified (12.7%). We found a 21.4% prevalence in familial cases. No significant differences in the relation between age and clinical disease expression were identified. Survival free of cardiovascular death curves constructed from data in the literature seems not to overestimate the risk in our population. CONCLUSIONS: The identification of TTNtv in patients with DCM is frequent and provides relevant information about the disease prognosis. The risk of cardiovascular death should not be underestimated. Age related penetrance need to be considered in the familial evaluation.

Mutations in TRIM63 cause an autosomal-recessive form of hypertrophic cardiomyopathy.

OBJECTIVE: Up to 50% of patients with hypertrophic cardiomyopathy (HCM) show no disease-causing variants in genetic studies. TRIM63 has been suggested as a candidate gene for the development of cardiomyopathies, although evidence for a causative role in HCM is limited. We sought to investigate the relationship between rare variants in TRIM63 and the development of HCM. METHODS: TRIM63 was sequenced by next generation sequencing in 4867 index cases with a clinical diagnosis of HCM and in 3628 probands with other cardiomyopathies. Additionally, 3136 index cases with familial cardiovascular diseases other than cardiomyopathy (mainly channelopathies and aortic diseases) were used as controls. RESULTS: Sixteen index cases with rare homozygous or compound heterozygous variants in TRIM63 (15 HCM and one restrictive cardiomyopathy) were included. No homozygous or compound heterozygous were identified in the control population. Familial evaluation showed that only homozygous and compound heterozygous had signs of disease, whereas all heterozygous family members were healthy. The mean age at diagnosis was 35 years (range 15-69). Fifty per cent of patients had concentric left ventricular hypertrophy (LVH) and 45% were asymptomatic at the moment of the first examination. Significant degrees of late gadolinium enhancement were detected in 80% of affected individuals, and 20% of patients had left ventricular (LV) systolic dysfunction. Fifty per cent had non-sustained ventricular tachycardia. Twenty per cent of patients suffered an adverse cerebrovascular event (20%). CONCLUSION: TRIM63 appears to be an uncommon cause of HCM inherited in an autosomal-recessive manner and associated with concentric LVH and a high rate of LV dysfunction.

Aportes de la genética al estudio y manejo clínico de las miocardiopatías / Genetic contributions to the study and clinical management of cardiomyopathies

Resumen: Las miocardiopatías son patologías muy heterogéneas asociadas a muerte súbita en jóvenes, cuyo diagnóstico y pronóstico son difíciles de establecer. El estudio genético puede ser una herramienta importante para el abordaje de estos pacientes y sus familias. Son generalmente patologías monogénicas, con penetrancia incompleta y expresividad clínica variable. Múltiples causas genéticas subyacen a la misma patología y un mismo gen puede estar asociado con fenotipos diferentes. La tecnología disponible en la actualidad permite analizar todos los genes importantes para cada fenotipo, con costos y tiempos de entrega de los resultados muy razonables. La rentabilidad del estudio genético depende de cada patología y de la probabilidad pretest de cada paciente particular. La interpretación de un estudio genético es una tarea compleja y un aspecto limitante para una correcta implementación clínica. Depende de múltiples variables y deberá ser realizado por equipos multidisciplinares con experiencia clínica en las patologías y los genes asociados. Un estudio genético positivo aportará mucha información diagnóstica y pronóstica para el paciente y su familia. Esto permitirá hacer recomendaciones en el estilo de vida, seleccionar tratamientos específicos para determinadas patologías, y decidir con más precisión el momento oportuno para implementar técnicas preventivas invasivas. Está demostrado que el screening genético en cascada luego de un resultado positivo es una estrategia costo-efectiva, que permite grandes ahorros en seguimientos clínicos innecesarios para focalizar los recursos en individuos genéticamente predispuestos.

Summary: Cardiomyopathies are heterogeneous diseases associated with sudden death in the young. The diagnosis and associated prognosis is sometimes difficult to establish. The genetic study could be an important tool for the clinical work-up of patients and families with these diseases. Cardiomyopathies are usually monogenic diseases, with incomplete penetrance and variable clinical expressivity. Several genes are associated with the same phenotype, and a particular gene could be related with different diseases. All the genes related with a particular phenotype could be study with the available sequencing technology at a reasonable price and turnaround time for the results. The yield of genetic tests depends on the type of cardiomyopathy and is specifically driven by the clinical pre-test probability of each case. The interpretation of genetic studies is complex and the main challenge for the correct clinical application of the results. Interpretation depends on several variables and should be performed by multidisciplinary teams with clinical and genetic expertise on cardiomyopathies. A positive genetic study could contribute with important diagnostic and prognostic information for the patient and the family. This information could be useful for life-style modifications, specific treatment selection and, in some cases, to decide the correct moment for primary prevention device's implantation. Cascade family screening after a positive genetic diagnosis is a cost-effective strategy for health-care systems.

Formin Homology 2 Domain Containing 3 (FHOD3) Is a Genetic Basis for Hypertrophic Cardiomyopathy.

BACKGROUND: The genetic cause of hypertrophic cardiomyopathy remains unexplained in a substantial proportion of cases. Formin homology 2 domain containing 3 (FHOD3) may have a role in the pathogenesis of cardiac hypertrophy but has not been implicated in hypertrophic cardiomyopathy. OBJECTIVES: This study sought to investigate the relation between FHOD3 mutations and the development of hypertrophic cardiomyopathy. METHODS: FHOD3 was sequenced by massive parallel sequencing in 3,189 hypertrophic cardiomyopathy unrelated probands and 2,777 patients with no evidence of cardiomyopathy (disease control subjects). The authors evaluated protein-altering candidate variants in FHOD3 for cosegregation, clinical characteristics, and outcomes. RESULTS: The authors identified 94 candidate variants in 132 probands. The variants' frequencies were significantly higher in patients with hypertrophic cardiomyopathy (74 of 3,189 [2.32%]) than in disease control subjects (18 of 2,777 [0.65%]; p < 0.001) or in the gnomAD database (1,049 of 138,606 [0.76%]; p < 0.001). FHOD3 mutations cosegregated with hypertrophic cardiomyopathy in 17 families, with a combined logarithm of the odds score of 7.92, indicative of very strong segregation. One-half of the disease-causing variants were clustered in a small conserved coiled-coil domain (amino acids 622 to 655); odds ratio for hypertrophic cardiomyopathy was 21.8 versus disease control subjects (95% confidence interval: 1.3 to 37.9; p < 0.001) and 14.1 against gnomAD (95% confidence interval: 6.9 to 28.7; p < 0.001). Hypertrophic cardiomyopathy patients carrying (likely) pathogenic mutations in FHOD3 (n = 70) were diagnosed after age 30 years (mean 46.1 ± 18.7 years), and two-thirds (66%) were males. Of the patients, 82% had asymmetric septal hypertrophy (mean 18.8 ± 5 mm); left ventricular ejection fraction <50% was present in 14% and hypertrabeculation in 16%. Events were rare before age 30 years, with an annual cardiovascular death incidence of 1% during follow-up. CONCLUSIONS: FHOD3 is a novel disease gene in hypertrophic cardiomyopathy, accounting for approximately 1% to 2% of cases. The phenotype and the rate of cardiovascular events are similar to those reported in unselected cohorts. The FHOD3 gene should be routinely included in hypertrophic cardiomyopathy genetic testing panels.

Truncating FLNC Mutations Are Associated With High-Risk Dilated and Arrhythmogenic Cardiomyopathies.

BACKGROUND: Filamin C (encoded by the FLNC gene) is essential for sarcomere attachment to the plasmatic membrane. FLNC mutations have been associated with myofibrillar myopathies, and cardiac involvement has been reported in some carriers. Accordingly, since 2012, the authors have included FLNC in the genetic screening of patients with inherited cardiomyopathies and sudden death. OBJECTIVES: The aim of this study was to demonstrate the association between truncating mutations in FLNC and the development of high-risk dilated and arrhythmogenic cardiomyopathies. METHODS: FLNC was studied using next-generation sequencing in 2,877 patients with inherited cardiovascular diseases. A characteristic phenotype was identified in probands with truncating mutations in FLNC. Clinical and genetic evaluation of 28 affected families was performed. Localization of filamin C in cardiac tissue was analyzed in patients with truncating FLNC mutations using immunohistochemistry. RESULTS: Twenty-three truncating mutations were identified in 28 probands previously diagnosed with dilated, arrhythmogenic, or restrictive cardiomyopathies. Truncating FLNC mutations were absent in patients with other phenotypes, including 1,078 patients with hypertrophic cardiomyopathy. Fifty-four mutation carriers were identified among 121 screened relatives. The phenotype consisted of left ventricular dilation (68%), systolic dysfunction (46%), and myocardial fibrosis (67%); inferolateral negative T waves and low QRS voltages on electrocardiography (33%); ventricular arrhythmias (82%); and frequent sudden cardiac death (40 cases in 21 of 28 families). Clinical skeletal myopathy was not observed. Penetrance was >97% in carriers older than 40 years. Truncating mutations in FLNC cosegregated with this phenotype with a dominant inheritance pattern (combined logarithm of the odds score: 9.5). Immunohistochemical staining of myocardial tissue showed no abnormal filamin C aggregates in patients with truncating FLNC mutations. CONCLUSIONS: Truncating mutations in FLNC caused an overlapping phenotype of dilated and left-dominant arrhythmogenic cardiomyopathies complicated by frequent premature sudden death. Prompt implantation of a cardiac defibrillator should be considered in affected patients harboring truncating mutations in FLNC.

Inverted U-Shaped Relation Between the Risk of Sudden Cardiac Death and Maximal Left Ventricular Wall Thickness in Hypertrophic Cardiomyopathy.

BACKGROUND: Hypertrophic cardiomyopathy is associated with sudden cardiac death (SCD). Some studies have shown an association between risk of sudden death and left ventricular maximal wall thickness (MWT), but there are few data in patients with extreme hypertrophy. The aim of this study was to determine the relation between MWT and the risk of SCD. METHODS AND RESULTS: This is a multicenter, retrospective, longitudinal cohort study of 3673 adult (≥16 years) patients, previously used to develop and validate a risk prediction model for SCD (HCM Risk-SCD [hypertrophic cardiomyopathy risk-SCD]). There was an inverted U-shaped relation between MWT and the estimated 5-year risk of SCD. In patients with MWT≥35 mm (n=47; mean age, 33 years; 81% men), there was a single SCD end point (annual rate, 0.2%; 95% confidence interval, 0.03-1.60) and 3 additional cardiovascular events during a median follow-up of 9.5 years. Compared with patients with MWT≤14 mm, those with MWT≥35 mm did not have a higher risk for SCD (hazard ratio, 0.22; 95% confidence interval, 0.03-1.65), cardiovascular death (hazard ratio, 0.66; 95% confidence interval, 0.26-1.67), or all-cause mortality (hazard ratio, 0.73; 95% confidence interval, 0.32-1.69). CONCLUSIONS: The risk of SCD has a complex, nonlinear relationship to MWT. The pathophysiological mechanisms behind this observation require further study but implantable cardioverter defibrillator implantation should not be guided solely on the severity of left ventricular hypertrophy.

Calmodulin 2 Mutation N98S Is Associated with Unexplained Cardiac Arrest in Infants Due to Low Clinical Penetrance Electrical Disorders.

BACKGROUND: Calmodulin 1, 2 and 3 (CALM) mutations have been found to cause cardiac arrest in children at a very early age. The underlying aetiology described is long QT syndrome (LQTS), catecholaminergic polymorphic ventricular tachycardia (CPVT) and idiopathic ventricular fibrillation (IVF). Little phenotypical data about CALM2 mutations is available. OBJECTIVES: The aim of this paper is to describe the clinical manifestations of the Asn98Ser mutation in CALM2 in two unrelated children in southern Spain with apparently unexplained cardiac arrest/death. METHODS: Two unrelated children aged 4 and 7, who were born to healthy parents, were studied. Both presented with sudden cardiac arrest. The first was resuscitated after a VF episode, and the second died suddenly. In both cases the baseline QTc interval was within normal limits. Peripheral blood DNA was available to perform targeted gene sequencing. RESULTS: The surviving 4-year-old girl had a positive epinephrine test for LQTS, and polymorphic ventricular ectopic beats were seen on a previous 24-hour Holter recording from the deceased 7-year-old boy, suggestive of a possible underlying CPVT phenotype. A p.Asn98Ser mutation in CALM2 was detected in both cases. This affected a highly conserved across species residue, and the location in the protein was adjacent to critical calcium binding loops in the calmodulin carboxyl-terminal domain, predicting a high pathogenic effect. CONCLUSIONS: Human calmodulin 2 mutation p.Asn98Ser is associated with sudden cardiac death in childhood with a variable clinical penetrance. Our results provide new phenotypical information about clinical behaviour of this mutation.