Revisiting the Diagnostic Yield of Hypertrophic Cardiomyopathy Genetic Testing

Clinical Effect of Genetic Testing in Inherited Cardiovascular Diseases: A 14-Year Retrospective Study

BACKGROUND

The clinical impact of genetic testing in a contemporary real-life cohort of patients with heritable cardiomyopathies or arrhythmias is not well defined. Additionally, the genetic spectrum of these conditions in the French-Canadian population is unknown, and interpretation of genetic variants can be challenging because of a known founder effect.

OBJECTIVES

This study sought to evaluate the clinical utility of arrhythmia and cardiomyopathy genetic testing and assess the utility of allele frequency data from a local reference population.

METHODS

The study included consecutive probands seen at the Montreal Heart Institute Cardiovascular Genetics Centre (Montreal, Quebec, Canada) for suspected heritable cardiomyopathies or arrhythmias for which both clinical data and genetic testing results were available. The study analyzed the enrichment of recurrent rare genetic variants by comparing their prevalence in the case cohort with that of a local population cohort.

RESULTS

A total of 2,062 probands (mean age at diagnosis 47 ± 17 years) were included. Overall, genetic testing identified a pathogenic/likely pathogenic (P/LP) variant in 496 (24%) probands. A total of 9 variants had their classification changed after comparing their prevalence (case control enrichment) using a local population-based cohort. Genetic testing resulted in diagnostic refinement with a potential impact on clinical management in 168 (8%) probands.

CONCLUSIONS

Genetic testing in a clinical context identified a disease-causing variant in 24% of probands, thus highlighting the high yield of rare variant genetic testing. Beyond the impact on family screening, the genetic testing result affected clinical management. Access to allele frequency data from a local population refines variant interpretation and classification.

Low Penetrance Sarcomere Variants Contribute to Additive Risk in Hypertrophic Cardiomyopathy

BACKGROUND

Classically, hypertrophic cardiomyopathy (HCM) has been viewed as a single-gene (monogenic) disease caused by pathogenic variants in sarcomere genes. Pathogenic sarcomere variants are individually rare and convey high risk for developing HCM (highly penetrant). Recently, important polygenic contributions have also been characterized. Low penetrance sarcomere variants (LowSVs) at intermediate frequencies and effect sizes have not been systematically investigated. We hypothesize that LowSVs may be common in HCM with substantial influence on disease risk and severity.

METHODS

Among all sarcomere variants observed in the Sarcomeric Human Cardiomyopathy Registry (SHaRe), we identified putative LowSVs defined by (1) population frequency greater than expected for highly penetrant (monogenic) HCM (allele frequency >5×10-5 in the Genome Aggregation Database, gnomAD) and (2) moderate enrichment (>2×) in patients with HCM compared with gnomAD. LowSVs were examined for their association with disease severity and clinical outcomes. Functional effects of selected LowSVs were assessed using induced pluripotent stem cell-derived cardiomyocytes. Association of LowSVs with HCM-adjacent traits in the general population was tested using UK Biobank cardiac magnetic resonance imaging data.

RESULTS

Among 6045 patients and 1159 unique variants in sarcomere genes, 12 LowSVs were identified. LowSVs were collectively common in the general population (1:350) and moderately enriched in HCM (aggregate odds ratio, 14.9 [95% CI, 12.5-17.9]). Isolated LowSVs were associated with an older age of HCM diagnosis and fewer adverse events. However, LowSVs in combination with a pathogenic sarcomere variant conferred higher morbidity (eg, composite adverse event hazard ratio, 5.4 [95% CI, 3.0-9.8] versus single pathogenic sarcomere variant, 2.0 [95% CI, 1.8-2.2]; P<0.001). An intermediate functional impact was validated for 2 specific LowSVs-MYBPC3 c.442G>A (partial splice gain) and TNNT2 c.832C>T (intermediate effect on contractile mechanics). Cardiac magnetic resonance imaging analysis of the general population revealed 5 of 12 LowSVs were significantly associated with HCM-adjacent traits without overt HCM.

CONCLUSIONS

This study establishes a new class of low penetrance sarcomere variants that are relatively common in the population. When penetrant, isolated LowSVs cause mild HCM. In combination with pathogenic sarcomere variants, LowSVs markedly increase disease severity, supporting a clinically significant additive effect. Last, LowSVs also contribute to age-related remodeling even in the absence of overt HCM.

Sex-Specific Clinical and Genetic Factors Associated With Adverse Outcomes in Hypertrophic Cardiomyopathy

BACKGROUND

Females with hypertrophic cardiomyopathy present at a more advanced stage of the disease and have a higher risk of heart failure and death. The factors behind these differences are unclear. We aimed to investigate sex-related differences in clinical and genetic factors affecting adverse outcomes in the Sarcomeric Human Cardiomyopathy Registry.

METHODS

Cox proportional hazard models were fit with a sex interaction term to determine if significant sex differences existed in the association between risk factors and outcomes. Models were fit separately for females and males to find the sex-specific hazard ratio (HR).

RESULTS

After a mean follow-up of 6.4 years, females had a higher risk of heart failure (HR, 1.51 [95% CI, 1.21-1.88]; P=0.0003) but a lower risk of atrial fibrillation (HR, 0.74 [95% CI, 0.59-0.93]; P<0.0001) and ventricular arrhythmia (HR, 0.60 [95% CI, 0.38-0.94]; P=0.027) than males. No sex difference was observed for death (P=0.84). Sarcomere-positive males had higher heart failure (HR, 1.34 [95% CI, 1.06-1.69]) and death risks (HR, 1.48 [95% CI, 1.08-2.04]) not seen in females (HR, 0.85 [95% CI, 0.66-1.08] versus HR, 0.86 [95% CI, 0.71-1.21]). MYBPC3 variants lowered heart failure risk in females (HR, 0.56 [95% CI, 0.41-0.77]) but not in males (HR, 1.29 [95% CI, 0.99-1.67]). A sex difference appeared in moderate (4% to <6%) versus low risk (<4%) European Society of Cardiology hypertrophic cardiomyopathy risk score, with females at moderate risk more prone to ventricular arrhythmia (HR, 3.57 [95% CI, 1.70-7.49]), unobserved in males (HR, 1.13 [95% CI, 0.63-2.03]).

CONCLUSIONS

We found that clinical and genetic factors contributing to adverse outcomes in hypertrophic cardiomyopathy affect females and males differently. Thus, research to inform sex-specific management of hypertrophic cardiomyopathy could improve outcomes for both sexes.

Unmasking Primary Carnitine Deficiency as a Mimic of Hypertrophic Cardiomyopathy

Primary carnitine deficiency may mimic hypertrophic cardiomyopathy and be mistakenly attributed to genotype-negative sarcomeric protein dysfunction in hypertrophic cardiomyopathy. Although rare, timely diagnosis may have significant implications on management and should prompt testing of family members.

Genetic Testing Practices and Pathological Assessments in Patients With End-stage Heart Failure Undergoing Heart Transplantation and Left Ventricular Assist Device Use

BACKGROUND

Genetic cardiomyopathies (CMs) are increasingly recognized as causes of end-stage heart failure (ESHF). Identification of a genetic etiology in ESHF has important prognostic and family implications. However, genetic testing practices are understudied in patients with ESHF.

METHODS

This single-center, retrospective study included consecutive patients with ESHF who underwent heart transplantation (HT) or left ventricular assist device (LVAD) implantation between 2018 and 2023. Data, including genetic testing and pathology reports, were collected from the electronic medical records. Analyses of demographic and clinical characteristics were stratified by genetic-testing completion and the presence of clinically actionable variants. Logistic regression was performed to evaluate for associations between histology findings and genetic variants.

RESULTS

A total of 529 adult patients (mean age 57 years) were included in the study and were predominantly male (79%, 422/529) and non-white (61%, 322/529). Genetic testing was performed in 54% (196/360) of patients with either nonischemic or mixed CMs. A clinically actionable result was identified in 36% (70/196) of patients, of whom only 43% (30/70) had genetic counselor referrals. The most common genetic variants were TTN (32%, 24/75), MYBPC3 (13%, 10/75) and TTR (11%, 8/75). Clinically actionable variants were identified in patients with known heart failure precipitators such as alcohol use. In multivariable analysis, the presence of interstitial fibrosis, specifically diffuse, on pathology was significantly associated with a clinically actionable variant (aOR 2.29, 95% CI [1.08-4.86]; P = 0.03).

CONCLUSION

Patients with ESHF and with nonischemic or mixed CM who were undergoing advanced therapies had low uptakes of genetic services, including testing and counselors, despite high burdens of genetic disease. Pathology findings such as interstitial fibrosis may provide insight into genetic etiology. The underuse of services suggests a need for implementation strategies to improve uptake.

Results of comprehensive genetic testing in patients presenting to a multidisciplinary inherited heart disease clinic in India

OBJECTIVES

This study aims to analyze the results of comprehensive genetic testing in patients presenting to a dedicated multidisciplinary inherited heart disease clinic in India.

METHODS

All patients presenting to our clinic from August 2017 to October 2023 with a suspected inherited heart disease and consenting for genetic testing were included. The probands were grouped into familial cardiomyopathies namely hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), arrhythmogenic cardiomyopathy (ACM) and peripartum cardiomyopathy (PPCM), channelopathies namely congenital long QT syndrome (LQTS) and Brugada syndrome (BrS), and heritable connective tissue disorder namely Marfan Syndrome (MFS). Next generation sequencing (NGS) was used, and pre-test and post-test counseling were provided to probands and cascade screening offered to relatives.

RESULTS

Mean age of the subjects (n = 77; 48 probands, 29 relatives) was 43 ± 18 years, 68 % male and 44 % symptomatic, with 36 HCM, 3 DCM, 3 ACM, 1 PPCM, 3 LQTS, 1 BrS and 1 MFS probands. The diagnostic yield of NGS-based genetic testing was 31 %; variants of uncertain significance (VUS) were identified in 54 %; and 15 % were genotype-negative. Twenty-nine relatives from 18 families with HCM (n = 12), DCM (n = 3), ACM (n = 2) and MFS (n = 1) underwent genetic testing. The genotype positive probands/relatives and VUS carriers with strong disease phenotype and/or high risk variant were advised periodic follow-up; the remaining probands/relatives were discharged from further clinical surveillance.

CONCLUSIONS

Genetic testing guides treatment and follow-up of patients with inherited heart diseases and should be carried out in dedicated multidisciplinary clinics with expertise for counseling and cascade screening of family members.

The challenge of risk stratification in hypertrophic cardiomyopathy: Clinical, genetic and imaging insights from a quaternary referral centre

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the commonest genetic cardiomyopathy and may result in sudden cardiac death (SCD). Clinical risk stratification scores are utilised to estimate SCD risk and determine potential utility of a primary prevention implantable cardioverter defibrillator (ICD).

METHODS

Patients with a confirmed diagnosis of HCM from a quaternary HCM service were defined according to clinical characteristics, genetic profiles and cardiac imaging results. European Risk-SCD score and American Heart Association / American College of Cardiology (AHA/ACC) Score were calculated. The primary outcome was cardiac arrest.

RESULTS

380 patients with HCM were followed up for a median of 6.4 years. 18 patients (4.7%) experienced cardiac arrest, with predictive factors being younger age (37.2 vs 54.4 years, p = 0.0041), unexplained syncope (33.3% vs 9.4%, p = 0.007), non-sustained ventricular tachycardia (50.0% vs 12.7%, p < 0.0001), increased septal thickness (21.5 vs 17.5 mm, p = 0.0003), and presence of a sarcomeric gene mutation (100.0% vs 65.8%, p = 0.038). The Risk-SCD and AHA/ACC scores had poor agreement (kappa coefficient 0.38). Risk-SCD score had poor sensitivity (44.4%), classifying 55.6% of patients with cardiac arrest as low-risk but was highly specific (93.7%). AHA/ACC risk score did not discriminate between groups significantly. 20 patients (5.3%) died, with most >60-year-olds having a non-cardiac cause of death (p = 0.0223).

CONCLUSION

This study highlights limited (38%) agreement between the Risk-SCD and AHA/ACC scores. Most cardiac arrests occurred in ostensibly low or medium-risk patients under both scores. Appropriate ICD selection remains challenging. Incorporating newer risk markers such as HCM genotyping and myocardial fibrosis quantification by cardiac MRI may assist future risk refinement.

The role of genetic testing in diagnosis and care of inherited cardiac conditions in a specialised multidisciplinary clinic

BACKGROUND

The diagnostic yield of genetic testing for inherited cardiac diseases is up to 40% and is primarily indicated for screening of at-risk relatives. Here, we evaluate the role of genomics in diagnosis and management among consecutive individuals attending a specialised clinic and identify those with the highest likelihood of having a monogenic disease.

METHODS

A retrospective audit of 1697 consecutive, unrelated probands referred to a specialised, multidisciplinary clinic between 2002 and 2020 was performed. A concordant clinical and genetic diagnosis was considered solved. Cases were classified as likely monogenic based on a score comprising a positive family history, young age at onset, and severe phenotype, whereas low-scoring cases were considered to have a likely complex aetiology. The impact of a genetic diagnosis was evaluated.

RESULTS

A total of 888 probands fulfilled the inclusion criteria, and genetic testing identified likely pathogenic or pathogenic (LP/P) variants in 330 individuals (37%) and suspicious variants of uncertain significance (VUS) in 73 (8%). Research-focused efforts identified 46 (5%) variants, missed by conventional genetic testing. Where a variant was identified, this changed or clarified the final diagnosis in a clinically useful way for 51 (13%). The yield of suspicious VUS across ancestry groups ranged from 15 to 20%, compared to only 10% among Europeans. Even when the clinical diagnosis was uncertain, those with the most monogenic disease features had the greatest diagnostic yield from genetic testing.

CONCLUSIONS

Research-focused efforts can increase the diagnostic yield by up to 5%. Where a variant is identified, this will have clinical utility beyond family screening in 13%. We demonstrate the value of genomics in reaching an overall diagnosis and highlight inequities based on ancestry. Acknowledging our incomplete understanding of disease phenotypes, we propose a framework for prioritising likely monogenic cases to solve their underlying cause of disease.

The mechanics of the heart: zooming in on hypertrophic cardiomyopathy and cMyBP-C

Hypertrophic cardiomyopathy (HCM), a disease characterized by cardiac muscle hypertrophy and hypercontractility, is the most frequently inherited disorder of the heart. HCM is mainly caused by variants in genes encoding proteins of the sarcomere, the basic contractile unit of cardiomyocytes. The most frequently mutated among them is MYBPC3, which encodes cardiac myosin-binding protein C (cMyBP-C), a key regulator of sarcomere contraction. In this review, we summarize clinical and genetic aspects of HCM and provide updated information on the function of the healthy and HCM sarcomere, as well as on emerging therapeutic options targeting sarcomere mechanical activity. Building on what is known about cMyBP-C activity, we examine different pathogenicity drivers by which MYBPC3 variants can cause disease, focussing on protein haploinsufficiency as a common pathomechanism also in nontruncating variants. Finally, we discuss recent evidence correlating altered cMyBP-C mechanical properties with HCM development.

Phenotypic Expression and Outcomes in Individuals With Rare Genetic Variants of Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is caused by rare variants in sarcomere-encoding genes, but little is known about the clinical significance of these variants in the general population.

OBJECTIVES

The goal of this study was to compare lifetime outcomes and cardiovascular phenotypes according to the presence of rare variants in sarcomere-encoding genes among middle-aged adults.

METHODS

This study analyzed whole exome sequencing and cardiac magnetic resonance imaging in UK Biobank participants stratified according to sarcomere-encoding variant status.

RESULTS

The prevalence of rare variants (allele frequency <0.00004) in HCM-associated sarcomere-encoding genes in 200,584 participants was 2.9% (n = 5,712; 1 in 35), and the prevalence of variants pathogenic or likely pathogenic for HCM (SARC-HCM-P/LP) was 0.25% (n = 493; 1 in 407). SARC-HCM-P/LP variants were associated with an increased risk of death or major adverse cardiac events compared with controls (hazard ratio: 1.69; 95% confidence interval [CI]: 1.38-2.07; P < 0.001), mainly due to heart failure endpoints (hazard ratio: 4.23; 95% CI: 3.07-5.83; P < 0.001). In 21,322 participants with both cardiac magnetic resonance imaging and whole exome sequencing, SARC-HCM-P/LP variants were associated with an asymmetric increase in left ventricular maximum wall thickness (10.9 ± 2.7 mm vs 9.4 ± 1.6 mm; P < 0.001), but hypertrophy (≥13 mm) was only present in 18.4% (n = 9 of 49; 95% CI: 9%-32%). SARC-HCM-P/LP variants were still associated with heart failure after adjustment for wall thickness (hazard ratio: 6.74; 95% CI: 2.43-18.7; P < 0.001).

CONCLUSIONS

In this population of middle-aged adults, SARC-HCM-P/LP variants have low aggregate penetrance for overt HCM but are associated with an increased risk of adverse cardiovascular outcomes and an attenuated cardiomyopathic phenotype. Although absolute event rates are low, identification of these variants may enhance risk stratification beyond familial disease.

Cardiovascular genetics: the role of genetic testing in diagnosis and management of patients with hypertrophic cardiomyopathy

Genetic testing in hypertrophic cardiomyopathy (HCM) is a valuable tool to manage patients and their families. Genetic testing can help inform diagnosis and differentiate HCM from other disorders that also result in increased left ventricular wall thickness, thereby directly impacting treatment. Moreover, genetic testing can definitively identify at-risk relatives and focus family management. Pathogenic variants in sarcomere and sarcomere-related genes have been implicated in causing HCM, and targeted gene panel testing is recommended for patients once a clinical diagnosis has been established. If a pathogenic or likely pathogenic variant is identified in a patient with HCM, predictive genetic testing is recommended for their at-risk relatives to determine who is at risk and to guide longitudinal screening and risk stratification. However, there are important challenges and considerations to implementing genetic testing in clinical practice. Genetic testing results can have psychological and other implications for patients and their families, emphasising the importance of genetic counselling before and after genetic testing. Determining the clinical relevance of genetic testing results is also complex and requires expertise in understanding of human genetic variation and clinical manifestations of the disease. In this review, we discuss the genetics of HCM and how to integrate genetic testing in clinical practice.