Genetic Testing For Hypertrophic Cardiomyopathy Research Articles

Genetic testing and counseling for hypertrophic cardiomyopathy: An evidence-based practice resource oftheNational Society of Genetic Counselors.

Hypertrophic cardiomyopathy (HCM) is a common hereditary condition affecting approximately 1 in 500 adults. It is characterized by marked clinical heterogeneity with individuals experiencing minimal to no symptoms, while others may have more severe outcomes including heart failure and sudden cardiac death. Genetic testing for HCM is increasingly available due to advances in DNA sequencing technologies and reduced costs. While a diagnosis of HCM is a well-supported indication for genetic testing and genetic counseling, incorporation of genetic services into the clinical setting is often limited outside of expert centers. As genetic counseling and testing have become more accessible and convenient, optimal integration of genomic data into the clinical care of individuals with HCM should be instituted, including delivery via genetic counseling. Drawing on recommendations from recent disease guidelines and systematic evidence reviews, we highlight key recommendations for HCM genetic testing and counseling. This practice resource provides a comprehensive framework to guide healthcare providers in the process of genetic test selection, variant classification, and cascade testing for genetic evaluation of HCM.

Enhancement of the Mayo Clinic Genotype Predictor Score using Cardiac MRI

Abstract Introduction Hypertrophic cardiomyopathy (HCM) is the most prevalent heritable cardiomyopathy typically transmitted in an autosomal dominant fashion. There is growing importance in identifying genetic test positive patients given its prognostic value. The Mayo HCM Genotype Predictor Score has been extensively validated for assessment of patient’s pre-test probability for genotype positive HCM and helps guide clinical decision-making based on clinical and echocardiographic variables. Herein, we evaluated the role of cardiac magnetic resonance (CMR) to enhance the genotype predictor score. Purpose Evaluate performance of the Mayo Clinic HCM Genotype Predictor Score using CMR variables, and develop an updated, CMR incorporated score. Methods Retrospective analysis was conducted on 175 unrelated HCM patients with at least 1 MRI and a HCM genetic testing seen at the Mayo Clinic between April 2004 and April 2018. Phenotyping information was obtained through review of electronic medical records. The original Mayo HCM Genotype Predictor Score was calculated using both echocardiography and clinical variables. An updated score was created incorporating CMR-specific variables. Diagnostic accuracy of the models was assessed thought Receiver Operating Characteristic (ROC) curves. Results Overall, 108 (62%) were males with a mean age at CMR of 51 ± 18 years. The yield of positive genetic test for the echocardiogram-derived Mayo HCM Genotype Predictor Score ranged from 38% for patients with -1 point to 100% for patients with 4 or 5 points. There was a significant incremental increase in diagnostic yield between score subgroups (p < 0.01) with an AUC of 0.659 (Figure 1A). Similar findings were observed using CMR variables (AUC of 0.697; Figure 1B). Univariate and multivariate analysis identified late gadolinium enhancement (LGE) as a strong predictor of a positive genetic test (OR 3.72; p=0.002), and it was added to the original score to create a new version. The Updated Mayo HCM Genotype Predictor Score predicted a positive genetic test ranging from 25% for patients with -1 point to 100% for patients with 5 or 6 points (p < 0.01). There was a significant increase in diagnostic accuracy when compared to the original score (AUC 0.724 vs 0.679; p=0.03; Figure 1C). Conclusion Using LGE, the updated CMR-based Mayo HCM Genotype Predictor score provides a simple and improved tool to aid in genetic counseling for HCM patients.

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.

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 15058: Critical Reappraisal of Genetic Variants in Hypertrophic Cardiomyopathy

Introduction: Hypertrophic cardiomyopathy (HCM) is a disease characterized by genotypic and phenotypic heterogeneity. Correct classification of genetic variation is critical for clinical interpretation. Herein, variants of uncertain significance (VUS) pose a dilemma in clinical practice, limiting physicians’ decision making and causing anguish to patients and family members. Furthermore, with increasing knowledge and changing guidelines, continuous reassessment is crucial to maintain usefulness in practice. This study sought to assess contemporary variant classification in a large cohort of patients with HCM. Methods: Retrospective analysis of all patients with HCM seen at Mayo Clinic and all patients with a variant in one of 8 genes with strong disease association for HCM were included. Genetic test reports were obtained from electronic health records along with their original variant classification assigned by either a commercial or research laboratory. Reassessment of variant pathogenicity was performed using the 2015 ACMG guideline criteria. Population frequency was obtained using Gnomad. Co-segregation presence or absence was determined by family history and co-segregation studies. Combined Annotation Dependent Depletion (CADD) was used as computational evidence of genetic deleterious effects for single nucleotide variants. Results: Between 2003 to 2019, a total of 1,782 patients underwent laboratory or commercial HCM genetic testing. Of these, 787 (44%) had positive genetic test with a variant at least 1 of the 8 genes. The original pathogenic classification was obtained for 754 patients. Of those, 430 (57%) variants where within the gene MYBPC3, 244 (32%) within MYH7 and 80 (11%) within either ACTC1, MYL2, MYL3, TINNI3, TNNT2 or TPM1. Overall, 222 patients (29%) originally had one or more variants classified as a VUS. Upon reassessment, 120 (54%) were reclassified as either pathogenic (33%), likely pathogenic (58%), benign (5%) or likely benign (3%). Conclusion: Periodic reassessment for HCM genetic variants, especially VUS, is critical for adequate patient care and management. Cascade screening could decrease patients’ uncertainty regarding their prognosis and management.

Abstract 14861: Decisional Factors Affecting Genetic Testing Uptake Among Black Adults With Hypertrophic Cardiomyopathy

Introduction: Black adults are underrepresented in hypertrophic cardiomyopathy (HCM) research and experience disparities in HCM - related variant interpretation due to a lack of diversity in genomic reference databases. This is compounded by lower HCM genetic testing utilization among this population. The objective of the qualitative study was to explore decisional factors affecting genetic testing use among a sample of Black adults with HCM. Methods: We used purposive sampling to recruit adults with clinical HCM and had undergone clinical genetic testing for HCM, self-identified as Black/African American, and were receiving care at a large urban academic center. Semi-structured individual interviews were conducted and inductive qualitative content analysis was performed to identify themes related to decisional factors for HCM genetic testing utilization. Quantitative descriptive analysis included demographics and genetic literacy evaluation via the Rapid Estimate of Adult Literacy in Genetics (REAL-G) Results: The sample included 30 individuals (15, 50% women), mean (SD) age 48.8 (17.2) years. Ten (33.3%) individuals had likely-pathogenic/pathogenic variants on clinical genetic testing. REAL-G scores were median (IQR) 62.5 (61;63), signifying a high-school literacy level. Almost half (46.7%) of participants reported finding at least some difficulty paying for basic necessities. The most common themes in decision-making regarding genetic testing utilization included out-of-pocket test costs and a positive relationship with HCM providers, followed by self-care and family concerns. Additional themes emerged concerning individual paths to an HCM diagnosis, including seeing multiple providers and navigating layers of the healthcare system, prior to evaluation by an HCM specialist. Conclusions: This study identified decisional facilitators regarding genetic testing use among a cohort of Black adults with HCM. Future work may focus on identifying barriers and designing interventions to improve genetic testing utilization in this population.

Characteristics of Patients With Obstructive Hypertrophic Cardiomyopathy in Real-World Community-Based Cardiovascular Practices

The clinical profile of patients with obstructive hypertrophic cardiomyopathy (oHC) is not well characterized, with little evidence outside selected referral populations. Using longitudinal medical claims data from a United States nationwide database, we retrospectively identified adults who were newly diagnosed with oHC. Clinical characteristics were compared from 1year before diagnosis and at the 2-year follow-up. Patients (N = 1,841) with oHC (age 63 ± 15years; 52% were male) with geographic representation across the United States were identified. Most patients received care within community-based cardiovascular practices and 7% at referral hypertrophic cardiomyopathy (HC) centers. Baseline diagnostic procedures included electrocardiogram (66%), echocardiogram (51%), magnetic resonance imaging (4%), and HC genetic testing (0.7%). Baseline co-morbidities were hypertension (59%), coronary artery disease (30%), diabetes (19%), and atrial fibrillation (19%). For all HC-related medications, use significantly increased after diagnosis. During follow-up, 144 patients (8%) received an implantable cardioverter-defibrillator for sudden death prevention, 99 underwent septal myectomy (5%), and 24 underwent alcohol septal ablation (1%). By the 1-year follow-up, 2% of patients had sudden cardiac arrest and 26% had atrial fibrillation, and heart failure increased from 16% to 27%. In conclusion, in a community-based population of patients with oHC, patients' age at diagnosis of oHC was older than reported for referral populations and patients had a significant co-morbidity burden. Cardiovascular medication use was appropriate, but the rate of guideline-supported surgical procedures was low.

Diagnostic validity and clinical utility of genetic testing for hypertrophic cardiomyopathy: a systematic review and meta-analysis

ObjectiveThis study summarises the diagnostic validity and clinical utility of genetic testing for patients with hypertrophic cardiomyopathy (HCM) and their at-risk relatives.MethodsA systematic search was performed in PubMed (MEDLINE), Embase,...

Further Considerations in Childhood-Onset Hypertrophic Cardiomyopathy Genetic Testing.

Further Considerations in Childhood-Onset Hypertrophic Cardiomyopathy Genetic Testing.

Sarcomere mutation negative hypertrophic cardiomyopathy is associated with ageing and obesity

BackgroundDespite advances in our understanding of the genetic causes of hypertrophic cardiomyopathy (HCM), a large portion of this patient population do not carry sarcomere gene mutations when screened. It remains...

Új lehetőség a szisztolés szívelégtelenség (HFrEF) kezelésében: omecamtiv-mecarbil

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disorder worldwide which exhibits considerable genetic heterogeneity. Widespread utilization of next-generation sequencing (NGS) in HCM has uncovered substantial genetic variation and highlighted the importance of a standardized approach to variant interpretation. According to this, accurate and consistent interpretation of sequence variants is essential for effective clinical care for individuals and their families with HCM. With this regard, the 2015 guidelines from the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) were widely applicable, but several elements lacked specificity for given genes or diseases. The latter guideline was adapted for the most frequent causative HCM gene, the beta myosin heavy chain gene (MYH7) by the ClinGen (Clinical Genome Resource) expert panel, the Inherited Cardiomyopathy Expert Panel. Due to the adaptation, the guideline became gene-specific, with general considerations which are widely adaptable for most of the causative genes in HCM. Based on the modified guideline, web-based interpretation algorithms have been developed which integrate data from population databases and define pathogenicity of different variants independent of the observer, therefore aiding standardized clinical interpretation of genetic testing. The latter approach serves as a basis for recommendation for genetic testing in the recent ACC/AHA HCM guideline published in 2020. The current review is meant to compile the latest advances in HCM genetic testing in clinical practice, while bringing into focus some of the ongoing challenges clinical geneticists are still facing. Although nowadays the interpretation of genetic findings is two steps closer to a more accurate approach due to gene adaptation and automatization, the multitude of putative causative genes have been once again reduced to the 8 sarcomere genes, a backward step.

Genetic diagnosis in hypertrophic cardiomyopathy: two steps forward, one step back

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disorder worldwide which exhibits considerable genetic heterogeneity. Widespread utilization of next-generation sequencing (NGS) in HCM has uncovered substantial genetic variation and highlighted the importance of a standardized approach to variant interpretation. According to this, accurate and consistent interpretation of sequence variants is essential for effective clinical care for individuals and their families with HCM. With this regard, the 2015 guidelines from the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) were widely applicable, but several elements lacked specificity for given genes or diseases. The latter guideline was adapted for the most frequent causative HCM gene, the beta myosin heavy chain gene (MYH7) by the ClinGen (Clinical Genome Resource) expert panel, the Inherited Cardiomyopathy Expert Panel. Due to the adaptation, the guideline became gene-specific, with general considerations which are widely adaptable for most of the causative genes in HCM. Based on the modified guideline, web-based interpretation algorithms have been developed which integrate data from population databases and define pathogenicity of different variants independent of the observer, therefore aiding standardized clinical interpretation of genetic testing. The latter approach serves as a basis for recommendation for genetic testing in the recent ACC/AHA HCM guideline published in 2020. The current review is meant to compile the latest advances in HCM genetic testing in clinical practice, while bringing into focus some of the ongoing challenges clinical geneticists are still facing. Although nowadays the interpretation of genetic findings is two steps closer to a more accurate approach due to gene adaptation and automatization, the multitude of putative causative genes have been once again reduced to the 8 sarcomere genes, a backward step.

Deep learning algorithm to improve hypertrophic cardiomyopathy mutation prediction using cardiac cine images.

The high variability of hypertrophic cardiomyopathy (HCM) genetic phenotypes has prompted the establishment of risk-stratification systems that predict the risk of a positive genetic mutation based on clinical and echocardiographic profiles. This study aims to improve mutation-risk prediction by extracting cardiovascular magnetic resonance (CMR) morphological features using a deep learning algorithm. We recruited 198 HCM patients (48% men, aged 47 ± 13years) and divided them into training (147 cases) and test (51 cases) sets based on different genetic testing institutions and CMR scan dates (2012, 2013, respectively). All patients underwent CMR examinations, HCM genetic testing, and an assessment of established genotype scores (Mayo Clinic score I, Mayo Clinic score II, and Toronto score). A deep learning (DL) model was developed to classify the HCM genotypes, based on a nonenhanced four-chamber view of cine images. The areas under the curve (AUCs) for the test set were Mayo Clinic score I (AUC: 0.64, sensitivity: 64.29%, specificity: 47.83%), Mayo Clinic score II (AUC: 0.70, sensitivity: 64.29%, specificity: 65.22%), Toronto score (AUC: 0.74, sensitivity: 75.00%, specificity: 56.52%), and DL model (AUC: 0.80, sensitivity: 85.71%, specificity: 69.57%). The combination of the DL and the Toronto score resulted in a significantly higher predictive performance (AUC = 0.84, sensitivity: 83.33%, specificity: 78.26%), compared with Mayo I (p = 006), Mayo II (p = 022), and Toronto score (p = 0.029). The combination of the DL model, based on nonenhanced cine CMR images and the Toronto score yielded significantly higher diagnostic performance in detecting HCM mutations. • Deep learning method could enable the extraction of image features from cine images. • Deep learning method based on cine images performed better than established scores in identifying HCM patients with positive genotypes. • The combination of the deep learning method based on cine images and the Toronto score could further improve the performance of the identification of HCM patients with positive genotypes.

Clinical Utility of a Phenotype-Enhanced MYH7-Specific Variant Classification Framework in Hypertrophic Cardiomyopathy Genetic Testing.

Missense variants in the MYH7-encoded MYH7 (beta myosin heavy chain 7) represent a leading cause of hypertrophic cardiomyopathy (HCM). MYH7-specific American College of Medical Genetics and Genomics (ACMG) variant classification guidelines were released recently but have yet to be assessed independently. We set out to assess the performance of the MYH7-specific ACMG guidelines and determine if the addition of phenotype-enhanced criteria (PE-ACMG) using the HCM Genotype Predictor Score can further reduce the burden of variants of uncertain significance (VUS). Re-assessment was performed on 70 MYH7-variants in 121 unique patients from Mayo Clinic, and an independent cohort of 54 variants in 70 patients from Royal Prince Alfred Hospital (Australia). Qualifying variants were re-adjudicated using both standard ACMG and MYH7-ACMG guidelines, and HCM Genotype Predictor Score was used to provide a validated measure of strength of clinical phenotype to be incorporated into the MYH7-ACMG framework. Among Mayo Clinic identified variants, 11/70 (16%) were classified as pathogenic (P), 10/70 (14%) as likely pathogenic, and 49/70 (70%) as a VUS. A similar distribution was seen in the Australian patients (12/54 [22%] P, 12/54 [22%] likely pathogenic, and 30/54 [56%] VUS; P=not significant). Application of the MYH7-ACMG resulted in a nonsignificant reduction of the VUS burden in both cohorts from 49/70 to 39/70 (56%; P=0.1; Mayo Clinic) and from 30/54 to 20/54 (37%; P=0.1; Australia). Using the combined PE-MYH7-ACMG framework, the VUS decreased significantly from 49 to 27 (P<0.001, Mayo Clinic) and from 30 to 16 (P<0.001; Australia). Use of the MYH7-specific guidelines alone failed to significantly decrease VUS burden in 2 independent cohorts. However, a significant reduction in VUS burden was observed after the addition of phenotypic criteria. Using a patient's strength of sarcomeric HCM phenotype for variant adjudication can increase significantly the clinical utility of genetic testing for patients with HCM.

Highlights From the Circulation Family of Journals

Highlights From the <i>Circulation</i> Family of Journals

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.

YIELD OF GENETIC TESTING FOR HYPERTROPHIC CARDIOMYOPATHY ACCORDING TO CONTEMPORARY VARIANT INTERPRETATION GUIDELINES: RESULTS FROM A LARGE CANADIAN REFERRAL CENTRE

The yield of genetic testing for hypertrophic cardiomyopathy (HCM) has been reported to be between 30% and 60%. Differences in populations studied are likely to be one explanation for this wide variation. Changes in the way we interpret genetic variants is likely to be a contributing factor. We aimed to analyze the genetic results from a large Canadian referral centre interpreted according to contemporary guidelines in order to examine the yield of genetic testing in the Canadian population. HCM index cases who underwent genetic testing between 2005 and January 2018 were included. All variants were re-classified according to the guidelines of the American College of Medical Genetics (ACMG) and subsequent gene-specific adaptations. Of 1,730 cases tested 393 (23%) were tested for 5 sarcomeric genes and 1,337 (77%) were tested for 8. In 325 patients (19%) a pathogenic (P) or likely pathogenic (LP) variant was identified and variants of unknown significance in 247 (14%). The majority (57%) of P/LP variants were found in the MYBPC3 gene, followed by the MYH7 gene (31%). The yield of TNNI3, TPM1 and TNNT2 genes was 4%, 3% and 2%, respectively. The 3 remaining genes combined (MYL2, MYL3 and ACTC1) were accountable for 3% of P/LP variants. Of the MYBPC3 variants 89% were loss-of-function (nonsense, frameshift or splice-site), one was an in-frame deletion and the rest (11%) missense. The yield of genetic testing in our centre was lower than previously reported. Possible explanations include lack of a founder mutation in the heterogenous Canadian population and higher referral rates of non-familial cases which are less likely to be gene-positive. Finally, using current and stricter guidelines for variant interpretation may have led to less variants being classified as P/LP, and may also explain the higher percentage of MYBPC3 variants among gene-positive cases. Further studies are required in order to determine whether this reflects the true genetic landscape of HCM or the limitations of current variant interpretation methods.