Testing For Hypertrophic Cardiomyopathy Research Articles

Diagnostic yield of head-up tilt table test in hypertrophic cardiomyopathy and unexplained syncope: the knot does not seem to be unraveling.

Conflicting results have been published considering the diagnostic performance of head-up tilt test (HUTT) in patients with hypertrophic cardiomyopathy (HCM). We aimed to conduct a meta-analysis to evaluate the diagnostic value of HUTT in the evaluation of unexplained syncope in patients with HCM. We performed a structured systematic database search using the following keywords: hypertrophic cardiomyopathy, syncope, unexplained syncope, head-up tilt test, tilt table test, tilt testing, orthostatic stress, autonomic function, autonomic response. Studies in which the HUTT was used to define autonomic dysfunction in patients with syncope at baseline or without syncope were included in the final analysis. A total of 252 HCM patients from 6 studies (159 patients without a history of syncope and 93 with a history of syncope, respectively) were evaluated. HUTT was positive in 50 (19.84%) of 252 patients (in 21 of 93 patients (22.58%) with a history of syncope and in 29 of 159 patients (18.24%) without a history of syncope, respectively). The pooled total sensitivity and specificity of the HUTT for detecting syncope were 22.1% (14.8-35.1%) and 83.6% (73.2-91.6%), respectively. The summary receiver operator curve showed that HUTT had an only modest discriminative ability for syncope with an area under the curve value of 0.565 (0.246-0.794). Although HUTT has significant limitations in diagnosis of unexplained syncope in patients with HCM, it may still be used to determine hypotensive susceptibility. Other autonomic tests can be used in diagnostic workflow in this population.

Clinical exome sequencing unravels the diverse spectrum of genetic heterogeneity and genotype-phenotype correlations in hypertrophic cardiomyopathy.

BackgroundCatalogues of pathogenic genetic mutations in hypertrophic cardiomyopathy (HCM) are disproportionately small when compared to that of the size of the population with South Asian ancestry and their collective increased risk of heart disease. MethodsWe conducted clinical exome sequencing of 200 HCM patients to identified cardiomyopathy-associated genetic mutations. The clinical and echocardiographic characteristics of genotype-positive and genotype-negative patients were compared, and the likelihood of detecting a positive genetic test result was evaluated. Allelic burden analysis was done to compare the minor allele frequencies (MAF) of the pathogenic or likely pathogenic (P/LP) variants and variants of uncertain significance (VUSs) identified in the cohort against various population genomics databases. ResultsThe genetic yield was 40% for P/LP variants, with MYBPC3 and MYH7 as the predominant sarcomere genes. Younger age-at-diagnosis, family history of HCM, asymmetric hypertrophic (ASH) pattern, the ratio of the interventricular septum to posterior wall thickness (IVS/PW ratio), left atrial (LA) dimensions, severe mitral regurgitation grade (MR grade), late gadolinium enhancement (LGE) detected fibrosis and absence of hypertension were associated with an increased likelihood of HCM-associated variants. Patients who experienced ventricular tachycardia and premature cardiovascular death were significantly likely to carry MYBPC3 or loss-of-function variants. LA and interventricular septal (IVS) dimensions were associated with MYH7 variants. The rare variant burden for P/LP variants and VUSs was significantly enriched in HCM cases compared to population controls. ConclusionOur study provides a comprehensive evaluation of HCM-associated genetic mutations from an Indian population. The identified genotype-phenotype associations could improve the yield of targeted genetic testing in HCM.

Genetic Testing in Hypertrophic Cardiomyopathy

Genetic testing is an important tool in the diagnosis and management of patients and families with hypertrophic cardiomyopathy (HCM). Modern testing can identify causative variants in 30 to >60% of patients, with probability of a positive test varying with baseline characteristics such as known family history of HCM. Patients diagnosed with HCM should be offered genetic counseling and genetic testing as appropriate. Standard multigene panels evaluate sarcomeric genes known to cause HCM as well as genetic conditions that can mimic HCM but require different management. Positive genetic testing (finding a pathogenic or likely pathogenic variant) helps to clarify diagnosis and assists in family screening. If there is high confidence that an identified variant is the cause of HCM, at-risk family members can pursue predictive testing to determine if they are truly at risk or if they can be dismissed from serial screening based on whether they inherited the family's causative variant. Interpreting test results can be complex, and providers should make use of multidisciplinary teams as well as evidence-based resources to obtain the best possible understanding of pathogenicity.

Electrophysiological mechanisms underlying T wave pseudonormalisation on stress ECGs in hypertrophic cardiomyopathy

BackgroundPseudonormal T waves may be detected on stress electrocardiograms (ECGs) in hypertrophic cardiomyopathy (HCM). Either myocardial ischaemia or purely exercise-induced changes have been hypothesised to contribute to this phenomenon, but the precise electrophysiological mechanisms remain unknown. MethodsComputational models of human HCM ventricles (n = 20) with apical and asymmetric septal hypertrophy phenotypes with variable severities of repolarisation impairment were used to investigate the effects of acute myocardial ischaemia on ECGs with T wave inversions at baseline. Virtual 12-lead ECGs were derived from a total of 520 biventricular simulations, for cases with regionally ischaemic K+ accumulation in hypertrophied segments, global exercise-induced serum K+ increases, and/or increased pacing frequency, to analyse effects on ECG biomarkers including ST segments, T wave amplitudes, and QT intervals. ResultsRegional ischaemic K+ accumulation had a greater impact on T wave pseudonormalisation than exercise-induced serum K+ increases, due to larger reductions in repolarisation gradients. Increases in serum K+ and pacing rate partially corrected T waves in some anatomical and electrophysiological phenotypes. T wave morphology was more sensitive than ST segment elevation to regional K+ increases, suggesting that T wave pseudonormalisation may sometimes be an early, or the only, ECG feature of myocardial ischaemia in HCM. ConclusionsIschaemia-induced T wave pseudonormalisation can occur on stress ECG testing in HCM before significant ST segment changes. Some anatomical and electrophysiological phenotypes may enable T wave pseudonormalisation due to exercise-induced increased serum K+ and pacing rate. Consideration of dynamic T wave abnormalities could improve the detection of myocardial ischaemia in HCM.

A pilot study of “burst” exercise testing in hypertrophic cardiomyopathy

A pilot study of “burst” exercise testing in hypertrophic cardiomyopathy

Gene-echocardiography: refining genotype-phenotype correlations in hypertrophic cardiomyopathy.

This study aims to clarify the association between hypertrophic patterns and genetic variants in hypertrophic cardiomyopathy (HCM) patients, contributing to the advancement of personalized management strategies for HCM. A comprehensive evaluation of genetic mutations was conducted in 392 HCM-affected families using Whole Exome Sequencing. Concurrently, relevant echocardiographic data from these individuals were collected. Our study revealed an increased susceptibility to enhanced septal and interventricular septal thickness in HCM patients harbouring gene mutations compared with those without. Mid-septal hypertrophy was found to be associated predominantly with myosin binding protein C3 (MYBPC3) variants, while a higher septum-to-posterior wall ratio correlated with myosin heavy chain 7 (MYH7) variants. Mutations in MYH7, MYBPC3, and other sarcomeric or myofilament genes (troponin I3 [TNNI3], tropomyosin 1 [TPM1], and troponin T2 [TNNT2]) showed a relationship with increased hypertrophy in the anterior wall, interventricular septum, and lateral wall of the left ventricle. In contrast, alpha kinase 3 (ALPK3)-associated hypertrophy chiefly presented in the apical region, while hypertrophy related to titin (TTN) and obscurin (OBSCN) mutations exhibited a uniform distribution across the myocardium. Hypertrophic patterns varied with the type and category of gene mutations, offering valuable diagnostic insights. Our findings underscore a strong link between hypertrophic patterns and genetic variants in HCM, providing a foundation for more accurate genetic testing and personalized management of HCM patients. The novel concept of 'gene-echocardiography' may enhance the precision and efficiency of genetic counselling and testing in HCM.

The Role of Cardiopulmonary Exercise Testing in Hypertrophic Cardiomyopathy.

This review emphasizes the importance of cardiopulmonary exercise testing (CPET) in patients diagnosed with hypertrophic cardiomyopathy (HCM). In contrast to standard exercise testing and stress echoes, which are limited due to the ECG changes and wall motion abnormalities that characterize this condition, CPET allows for the assessment of the complex pathophysiology and severity of the disease, its mechanisms of functional limitation, and its risk stratification. It is useful tool to evaluate the risk for sudden cardiac death and select patients for cardiac resynchronization therapy (CRT), cardiac transplantation, or mechanical circulatory support, especially when symptomatology and functional status are uncertain. It may help in differentiating HCM from other forms of cardiac hypertrophy, such as athletes' heart. Finally, it is used to guide and monitor therapy as well as for exercise prescription. It may be considered every 2 years in clinically stable patients or every year in patients with worsening symptoms. Although performed only in specialized centers, CPET combined with echocardiography (i.e., CPET imaging) and invasive CPET are more informative and provide a better assessment of cardiac functional status, left ventricular outflow tract obstruction, and diastolic dysfunction during exercise in patients with HCM.

Genetic Testing and Counselling in Hypertrophic Cardiomyopathy: Frequently Asked Questions

Genetic counselling and genetic testing in hypertrophic cardiomyopathy (HCM) represent an integral part of the diagnostic algorithm to confirm the diagnosis, distinguish it from phenocopies, and suggest tailored therapeutic intervention strategies. Additionally, they enable cascade genetic testing in the family. With the implementation of Next Generation Sequencing technologies (NGS), the interpretation of genetic data has become more complex. In this regard, cardiologists play a central role, aiding geneticists to correctly evaluate the pathogenicity of the identified genetic alterations. In the ideal setting, geneticists and cardiologists must work side by side to diagnose HCM as well as convey the correct information to patients in response to their many questions and concerns. After a brief overview of the role of genetics in the diagnosis of HCM, we present and discuss the frequently asked questions by HCM patients throughout our 20-year genetic counselling experience. Appropriate communication between the team and the families is key to the goal of delivering the full potential of genetic testing to our patients.

1152 INVESTIGATION ON THE HIGH INCIDENCE OF THE ATTRV-CAUSING TRANSTHYRETIN VARIANT VAL142ILE IN CENTRAL ITALY

Abstract The p.Val142Ile variant in transthyretin (encoded by the TTR gene) is the most common genetic cause of transthyretin-related amyloidosis. This allele is particularly prevalent in communities of African descent compared with populations of different ancestries, where its frequency is two orders of magnitude lower. For this reason, p.Val142Ile has always been considered an “African” variant, with limited studies performed on individuals of European descent. However, recent reports of higher-than-expected prevalence in European-ancestry populations question the African specificity of this allele. Here we show that the high recurrence of p.Val142Ile in central Italy is due to a founder effect and not to recent admixture from African populations, highlighting how this may be the case in other communities. This suggests a probable underestimate of the global prevalence of p.Val142Ile, and further emphasizes the importance of routine inclusion of TTR in gene panels used for clinical genetic testing in hypertrophic cardiomyopathy (independently of the patient's geographical origin), that transthyretin-related amyloidosis can mimic. Figure.Principal Component Analysis (PCA) of the 16 probands together with the 25044 individuals of the 1000 Genomes Project (Phase 3) having been genotyped both within the 1000 Genomes Project (NA10851_1KG) and in-house (NA10851_internal). The proband clustering within the smear of native Americans is A228.

Investigation on the high recurrence of the ATTRv-causing transthyretin variant Val142Ile in central Italy.

The p.Val142Ile variant in transthyretin (encoded by the TTR gene) is the most common genetic cause of transthyretin-related amyloidosis. This allele is particularly prevalent in communities ofAfrican descent compared with populations of different ancestries, where its frequency is two orders of magnitude lower. For this reason, p.Val142Ile has always been considered an "African" variant, with limited studies performed on individuals of European descent. However, recent reports of higher-than-expected prevalence in European-ancestry populations question the African specificity of this allele. Here we show that the high recurrence of p.Val142Ile in central Italy is due to a founder effect and not to recent admixture from African populations, highlighting how this may be the case in other communities. This suggests a probable underestimate of the global prevalence of p.Val142Ile, and further emphasizes the importance of routine inclusion of TTR in gene panels used for clinical genetic testing in hypertrophic cardiomyopathy (independently of the patient's geographical origin), that transthyretin-related amyloidosis can mimic.

Abstract 9492: Ventricular Tachycardia During Cardiopulmonary Exercise Testing in Hypertrophic Cardiomyopathy

Introduction and Hypothesis: In patients with hypertrophic cardiomyopathy (HCM), ventricular tachycardia (VT) is associated with adverse prognosis. Cardiopulmonary exercise testing (CPET) is part of the standard clinical evaluation in HCM. However, limited data are available on the incidence of VT and other adverse events during CPET in HCM. Methods: We reviewed the Mayo Clinic’s Integrated Stress Center Database for CPETs performed on HCM patients between January 2011 and July 2016. Patients were referred for clinical CPET by a physician, and medications were continued for the test. Electronic medical records were reviewed for clinical information and CPET data. Results: A total of 1,208 CPETs were performed on 976 HCM patients during the study period. Most tests were symptom-limited (94.6%), most common symptom was dyspnea (55%). Despite the relatively high number of patients with a history of VT (10.4%) and/or cardiac arrest (1.6%), there was a low rate of adverse events. Non-sustained VT occurred in 6 patients, most frequently during active recovery (3/6), and 2 of these 6 patients had prior history of VT. A 34 year-old female patient experienced sustained VT degenerating into ventricular fibrillation terminated by ICD shock. One patient had syncope during the test but no arrhythmia. Importantly, none of the patients died within 48 hours of the exercise test. Conclusions: In a large cohort of HCM patients, the incidence of VT or other adverse events was a rare finding during symptom-limited CPET.

Diagnostic yield from cardiac gene panel testing for inherited cardiac conditions in a large Irish cohort

Abstract Background Inherited cardiomyopathies (hypertrophic, dilated and arrhythmogenic) and cardiac ion channelopathies (long QT, Brugada and CPVT) predispose to sudden cardiac death/sudden arrhythmic death syndrome. Given their genetically heterogenous nature, multi-gene DNA sequencing panels are useful to aid genetic diagnosis. Purpose Investigate the diagnostic yield from cardiac gene panel testing undertaken in patients (including molecular autopsy in deceased patients) referred to four clinical services from 2002 to 2020. Methods Data was collected by interrogation of departmental databases, family charts, and review of molecular genetic diagnostic reports. Results We evaluated molecular genetic diagnostic results from 835 individuals (461 males, 374 females) from 824 families, including 58 deceased patients who underwent molecular autopsy. The median age of the cohort was 44 years (range 0.1–86 years). Testing for hypertrophic cardiomyopathy (HCM) and long QT syndrome (LQT) genes represented 36% and 32% of the cohort, respectively, with the remaining 32% accounting for other cardiomyopathies, arrhythmia syndromes or metabolic/syndromic diseases. The overall variant detection rate was 50% across all panel types. Three hundred and fifty patients (42%) carried a single variant, 68 patients (8%) carried multiple variants (up to a maximum of four), including two individuals who carried two actionable (pathogenic/likely pathogenic) variants each and 30 individuals (5%) with one actionable variant plus a variant of uncertain significance (VUS). The overall diagnostic yield of at least one actionable variant was 28%. At least one VUS was detected in 27% of the cohort. Molecular autopsy yielded an actionable variant in 10% of patients, while 30% of the subcohort carried at least one VUS (up to maximum of two). We found a positive association between female sex and the likelihood of detecting an actionable variant. By decade of age, detection of actionable variants ranged from 19% (60–69 years) to 41% (0–9 years). By panel type, actionable variants ranged from 14% (Brugada) to 35% (cardiomyopathy). The burden of VUS ranged from 22% (LQT) to 46% (dilated cardiomyopathy). Altogether 234 actionable variants were detected in 26 genes, including seven metabolic or syndromic disease genes. From those with non-metabolic/syndromic forms of disease, 84% of actionable variants were detected in well established ICC genes. Analysis of gene-disease associations for VUS detected from HCM and LQT panels revealed that 10–25% were detected in genes now deemed to have only moderate or limited evidence of disease causation. Conclusion Most actionable variants in this cohort were detected in well-established ICC genes, suggesting that large gene panels offer little extra sensitivity compared to historic smaller gene panels. Despite recent gene curation efforts, the high burden of VUS remains a considerable challenge in ICC management. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): National Children's Research Centre

Prognostic relevance of exercise testing in hypertrophic cardiomyopathy. A systematic review

BackgroundCardiopulmonary exercise test (CPET) is indicated as part of the assessment in hypertrophic cardiomyopathy (HCM) patients and stress echocardiography is often used to assess symptoms. However, the role of exercise testing for prognostic stratification in HCM is still not established. AimsTo systematically review the evidence on the role of exercise testing for prognostic stratification in hypertrophic cardiomyopathy. MethodsA systematic review was conducted for eligible publications, between 2010 and 2020, that included evaluation of outcomes and prognosis. In these studies, patients underwent exercise echocardiography and/or cardiopulmonary exercise testing, performed according to predefined protocols. Diverse parameters were assessed in order to determine which were relevant for the prognosis. Analyzed outcomes included death from any cause, sudden cardiac death (SCD) and equivalents, cardiovascular death, heart failure requiring hospitalization or progression to New York Heart Association classes III or IV, cardiac transplantation, non-sustained ventricular tachycardia, stroke, myocardial infarction and invasive septal reduction therapy. ResultsEighteen publications were included, corresponding to a total of 7525 patients. The mean follow-up period varied between 1 and 8 years. The main findings of these studies revealed that the major predictors of outcomes were abnormal heart rate recovery, abnormal blood pressure response exercise induced wall motion abnormalities, lower peak VO2, higher VE/VCO2, and pulmonary hypertension/exercise-induced pulmonary hypertension. ConclusionAlthough most studies concluded that exercise test results are useful to determine prognosis in HCM, further investigation is needed regarding whether it adds independent value to the current risk stratification strategies.

Diagnostic yield of genetic testing in a heterogeneous cohort of 1376 HCM patients

BackgroundGenetic testing in hypertrophic cardiomyopathy (HCM) is a published guideline-based recommendation. The diagnostic yield of genetic testing and corresponding HCM-associated genes have been largely documented by single center studies and carefully selected patient cohorts. Our goal was to evaluate the diagnostic yield of genetic testing in a heterogeneous cohort of patients with a clinical suspicion of HCM, referred for genetic testing from multiple centers around the world.MethodsA retrospective review of patients with a suspected clinical diagnosis of HCM referred for genetic testing at Blueprint Genetics was undertaken. The analysis included syndromic, myopathic and metabolic etiologies. Genetic test results and variant classifications were extracted from the database. Variants classified as pathogenic (P) or likely pathogenic (LP) were considered diagnostic.ResultsA total of 1376 samples were analyzed. Three hundred and sixty-nine tests were diagnostic (26.8%); 373 P or LP variants were identified. Only one copy number variant was identified. The majority of diagnostic variants involved genes encoding the sarcomere (85.0%) followed by 4.3% of diagnostic variants identified in the RASopathy genes. Two percent of diagnostic variants were in genes associated with a cardiomyopathy other than HCM or an inherited arrhythmia. Clinical variables that increased the likelihood of identifying a diagnostic variant included: an earlier age at diagnosis (p < 0.0001), a higher maximum wall thickness (MWT) (p < 0.0001), a positive family history (p < 0.0001), the absence of hypertension (p = 0.0002), and the presence of an implantable cardioverter-defibrillator (ICD) (p = 0.0004).ConclusionThe diagnostic yield of genetic testing in this heterogeneous cohort of patients with a clinical suspicion of HCM is lower than what has been reported in well-characterized patient cohorts. We report the highest yield of diagnostic variants in the RASopathy genes identified in a laboratory cohort of HCM patients to date. The spectrum of genes implicated in this unselected cohort highlights the importance of pre-and post-test counseling when offering genetic testing to the broad HCM population.

Deletions of specific exons of FHOD3 detected by next-generation sequencing are associated with hypertrophic cardiomyopathy.

Despite new strategies, such as evaluating deep intronic variants and new genes in whole-genome-sequencing studies, the diagnostic yield of genetic testing in hypertrophic cardiomyopathy (HCM) is still around 50%. FHOD3 has emerged as a novel disease-causing gene for this phenotype, but the relevance and clinical implication of copy-number variations (CNVs) have not been determined. In this study, CNVs were evaluated using a comparative depth-of-coverage strategy by next-generation sequencing (NGS) in 5493 HCM probands and 2973 disease-controls. We detected three symmetrical deletions in FHOD3 that involved exons 15 and 16 in three HCM families (no CNVs were detected in the control group). These exons are part of the diaphanous inhibitory domain of FHOD3 protein, considered a cluster of mutations for HCM. The clinical characteristics of the affected carriers were consistent with those reported in FHOD3 in previous studies. This study highlights the importance of performing CNV analysis systematically in NGS genetic testing panels for HCM, and reinforces the relevance of the FHOD3 gene in the disease.

Clinical and ECG variables to predict the outcome of genetic testing in hypertrophic cardiomyopathy

Knowledge on the influence of specific genotypes on the phenotypic expression of hypertrophic cardiomyopathy (HCM) is emerging. The objective of this study was to evaluate the genotype-phenotype relation in HCM patients and to construct a score to predict the genetic yield based to improve counseling. Unrelated HCM patients who underwent genetic testing were included in the analysis. Multivariate logistic regression was performed to identify variables that predict a positive genetic test. A weighted score was constructed based on the odds ratios. In total, 378 HCM patients were included of whom 141 carried a mutation (global yield 37%), 181 were mutation negative and 56 only carried a variant of unknown significance. We identified age at diagnosis <45 years, familial HCM, familial sudden death, arrhythmic syncope, maximal wall thickness ≥20 mm, asymmetrical hypertrophy and the absence of negative T waves in the lateral ECG leads as significant predictors of a positive genetic test. When we included these values in a risk score we found very high correlation between the score and the observed genetic yield (Pearson r = 0.98). MYBPC3 mutation carriers more frequently suffered sudden cardiac death compared to troponin complex mutations carriers (p = 0.01) and a similar trend was observed compared to MYH7 mutation carriers (p = 0.08) and mutation negative patients (p = 0.11). To conclude, a simple score system based on clinical variables can predict the genetic yield in HCM index patients, aiding in counseling HCM patients. MYBPC3 mutation carriers had a worse outcome regarding sudden cardiac death.

Highlights From the Circulation Family of Journals.

Highlights From the Circulation Family of Journals.

Defining the diagnostic effectiveness of genes for inclusion in panels: the experience of two decades of genetic testing for hypertrophic cardiomyopathy at a single center

PurposeGenetic testing in hypertrophic cardiomyopathy (HCM) has long relied on Sanger sequencing of sarcomeric genes. The advent of next-generation sequencing (NGS) has catalyzed routine testing of additional genes of dubious HCM-causing potential. We used 19 years of genetic testing results to define a reliable set of genes implicated in Mendelian HCM and assess the value of expanded NGS panels. MethodsWe dissected genetic testing results from 1,198 single-center HCM probands and devised a widely applicable score to identify which genes yield effective results in the diagnostic setting. ResultsCompared with early panels targeting only fully validated sarcomeric HCM genes, expanded NGS panels allow the prompt recognition of probands with HCM-mimicking diseases. Scoring by “diagnostic effectiveness” highlighted that PLN should also be routinely screened besides historically validated genes for HCM and its mimics. ConclusionThe additive value of expanded panels in HCM genetic testing lies in the systematic screening of genes associated with HCM mimics, requiring different patient management. Only variants in a limited set of genes are highly actionable and interpretable in the clinic, suggesting that larger panels offer limited additional sensitivity. A score estimating the relative effectiveness of a given gene’s inclusion in diagnostic panels is proposed.

Evaluating the Clinical Validity of Hypertrophic Cardiomyopathy Genes.

Genetic testing for families with hypertrophic cardiomyopathy (HCM) provides a significant opportunity to improve care. Recent trends to increase gene panel sizes often mean variants in genes with questionable association are reported to patients. Classification of HCM genes and variants is critical, as misclassification can lead to genetic misdiagnosis. We show the validity of previously reported HCM genes using an established method for evaluating gene-disease associations. A systematic approach was used to assess the validity of reported gene-disease associations, including associations with isolated HCM and syndromes including left ventricular hypertrophy. Genes were categorized as having definitive, strong, moderate, limited, or no evidence of disease causation. We also reviewed current variant classifications for HCM in ClinVar, a publicly available variant resource. Fifty-seven genes were selected for curation based on their frequent inclusion in HCM testing and prior association reports. Of 33 HCM genes, only 8 (24%) were categorized as definitive ( MYBPC3, MYH7, TNNT2, TNNI3, TPM1, ACTC1, MYL2, and MYL3); 3 had moderate evidence ( CSRP3, TNNC1, and JPH2; 33%); and 22 (66%) had limited (n=16) or no evidence (n=6). There were 12 of 24 syndromic genes definitively associated with isolated left ventricular hypertrophy. Of 4191 HCM variants in ClinVar, 31% were in genes with limited or no evidence of disease association. The majority of genes previously reported as causative of HCM and commonly included in diagnostic tests have limited or no evidence of disease association. Systematically curated HCM genes are essential to guide appropriate reporting of variants and ensure the best possible outcomes for HCM families.

Key Value of RNA Analysis of MYBPC3 Splice-Site Variants in Hypertrophic Cardiomyopathy.

MYBPC3 splicing errors are a common cause of hypertrophic cardiomyopathy (HCM). Variants affecting essential splice-site dinucleotides inhibit splicing, whereas the impact of variants at conserved flanking nucleotides is less clear. We evaluated the contribution of MYBPC3 splice-site variants in a large cohort of patients with HCM and assessed the impact on splicing with RNA analysis. Patients attending a specialized multidisciplinary clinic, with a clinical diagnosis of HCM and genetic testing of at least 46 cardiomyopathy-associated genes, were included. Patients with variants in MYBPC3 splice sites with in silico-predicted effects on splicing were selected. RNA was extracted from fresh venous blood or paraffin-embedded myocardial tissue of the patients, amplified, and sequenced. Variants were classified for pathogenicity using the American College of Medical Genetics and Genomics guidelines. We found 29 rare MYBPC3 splice-site variants in 56 of 557 (10%) unrelated HCM probands. Three variants were not predicted to alter RNA splicing, and 13 essential splice dinucleotide, nonsense, and short insertion or deletion variants were not further assessed. RNA analysis was performed on 9 variants (c.654+5G>C, c.772G>A, c.821+3G>T, c.927-9G>A, c.1090G>A, c.1624G>A, c.1624+4A>T, c.3190+5G>A, and c.3491-3C>G), and RNA splicing errors were confirmed for 7. Four variants in 4 families resulted in clinically meaningful reclassifications. After RNA analysis, 4 of 56 (7%) families with MYBPC3 splice-site variants were reclassified from uncertain clinical significance to likely pathogenic. RNA analysis of splice-site variants can assist in understanding pathogenicity and increase the diagnostic yield of genetic testing in HCM.