Founder mutations in hypertrophic cardiomyopathy patients in the Netherlands

Family screening for hypertrophic cardiomyopathy: Initial cardiologic assessment, and long-term follow-up of genotype-positive phenotype-negative individuals

AIMS

(i) Investigate the prevalence of hypertrophic cardiomyopathy (HCM) in individuals with pathogenic/likely pathogenic (P/LP) gene variants detected through family cascade testing in relatives, and (ii) evaluate phenotypic progression in genotype-positive phenotype-negative (G+/P-) individuals during follow-up.

RESULTS

From 2000 to 2023, 273 individuals underwent cardiologic evaluation following P/LP variant detection through family screening. Upon initial evaluation, HCM was diagnosed in 128 (47 %) individuals. Comparing with 145 G+/P- individuals, HCM patients were older (48 vs 38 years, p < 0.001) and more likely male (57 % vs 34 %, p < 0.001). During follow-up (median 11 years), 14 (11 %) of the HCM patients died (two from sudden cardiac death), four (3 %) underwent myectomy, 15 (12 %) developed atrial fibrillation and 17 (13 %) required implantable cardioverter-defibrillator implantation (15 primary prevention, 88 %). HCM-related adverse outcomes correlated with younger diagnosis age. During follow-up (median 8 years) of 118 (out of 145) G+/P- subjects with at least one year of follow-up, seven (6 %) individuals (71 % female, diagnosed age 39-77, after median follow-up 6 years) developed HCM (mean maximal wall thickness increasing from 10.2 mm to 13.3 mm). In this G+/P- cohort, significant echocardiographic changes from baseline to last visit were negligible. Over half (56 %) had <1 mm change of maximal wall thickness. No adverse cardiac outcomes occurred.

CONCLUSION

The initial evaluation was high-yield, with HCM being diagnosed in 47 % of G+ individuals, more frequently in older males. Over a median 8-year follow-up, 6 % of G+/P- individuals developed mild HCM, with no adverse cardiac outcomes. These data support initial screening in all first degree relatives, but (very) low-frequency cardiologic evaluations for G+/P- individuals thereafter.

Recreational and Occupational Physical Activity and Risk of Adverse Events in Truncating MYBPC3 Founder Variant Carriers

BACKGROUND

MYBPC3 founder variants cause hypertrophic cardiomyopathy leading to heart failure and malignant ventricular arrhythmias. Exercise is typically regarded as a risk factor for disease expression although evidence is conflicting. Stratifying by type of exercise may discriminate low- from high-risk activities in these patients. Here, we evaluate the effects of exercise, stratified by high-static and high-dynamic components, on the risk of major cardiomyopathy-related events (MCEs) and cardiomyopathy penetrance among MYBPC3 founder variant carriers.

METHODS

We interviewed 188 carriers (57.4% male; aged 43.0±15.0 years) on exercise participation since the age of 10 years. The exercise was quantified as the metabolic equivalent of task-h/wk before the presentation. MCE was defined as a composite of malignant ventricular arrhythmia (sustained ventricular tachycardia/fibrillation), heart failure (heart failure hospitalizations or transplantation), and septal reduction therapy. Static and dynamic exercises were defined per the Bethesda classification. Associations of exercise with MCE and cardiomyopathy penetrance were adjusted for sex and assessed using Cox regression.

RESULTS

Overall, 43 (22.9%) subjects experienced MCE and 139 (73.9%) were diagnosed with cardiomyopathy. No association was found between overall physical activity and high-static activity with MCE (P=0.587 overall; P=0.322 high static) or cardiomyopathy penetrance (P=0.317 overall; P=0.623 high static). In contrast, high-dynamic activity was associated with malignant ventricular arrhythmia (dichotomized at the 75th percentile: adjusted hazard ratio, 3.26 [95% CI, 1.26-8.44]; P=0.015).

CONCLUSIONS

Overall exercise participation does not generally increase the risk of adverse events among MYBPC3 founder variant carriers. Nonetheless, an increased risk of malignant ventricular arrhythmia was observed among those engaged in the highest quartile of high-dynamic sports, suggesting that high-level high-intensity exercise activities should be entertained with caution.

Phenotypic spectrum of the first Belgian MYBPC3 founder: a large multi-exon deletion with a varying phenotype

Background

Variants in the MYBPC3 gene are a frequent cause of hypertrophic cardiomyopathy (HCM) but display a large phenotypic heterogeneity. Founder mutations are often believed to be more benign as they prevailed despite potential negative selection pressure. We detected a pathogenic variant in MYBPC3 (del exon 23-26) in several probands. We aimed to assess the presence of a common haplotype and to describe the cardiac characteristics, disease severity and long-term outcome of mutation carriers.

Methods

Probands with HCM caused by a pathogenic deletion of exon 23-26 of MYBPC3 were identified through genetic screening using a gene panel encompassing 59 genes associated with cardiomyopathies in a single genetic center in Belgium. Cascade screening of first-degree relatives was performed, and genotype positive relatives were further phenotyped. Clinical characteristics were collected from probands and relatives. Cardiac outcomes included death, heart transplantation, life-threatening arrhythmia, heart failure hospitalization or septal reduction therapy. Haplotype analysis, using microsatellite markers surrounding MYBPC3, was performed in all index patients to identify a common haplotype. The age of the founder variant was estimated based on the size of the shared haplotype using a linkage-disequilibrium based approach.

Results

We identified 24 probands with HCM harbouring the MYBPC3 exon 23-26 deletion. Probands were on average 51 ± 16 years old at time of clinical HCM diagnosis and 62 ± 10 years old at time of genetic diagnosis. A common haplotype of 1.19 Mb was identified in all 24 probands, with 19 of the probands sharing a 13.8 Mb haplotype. The founder event was estimated to have happened five generations, or 175-200 years ago, around the year 1830 in central Flanders. Through cascade screening, 59 first-degree relatives were genetically tested, of whom 37 (62.7%) were genotype positive (G+) and 22 (37.3%) genotype negative (G-). They were on average 38 ± 19 years old at time of genetic testing. Subsequent clinical assessment revealed a HCM phenotype in 19 (51.4%) G+ relatives. Probands were older (63 ± 10 vs. 42 ± 21 years; p < 0.001) and had more severe phenotypes than G+ family members, presenting with more symptoms (50% vs. 13.5%; p = 0.002), arrhythmia (41.7% vs. 12.9%, p = 0.014), more overt hypertrophy and left ventricular outflow tract obstruction (43.5% vs. 3.0%; p < 0.001). Male G+ relatives more often had a HCM phenotype (78.6% vs. 34.8%; p = 0.010) and were more severely affected than females. At the age of 50, a penetrance of 78.6% was observed, defined as the presence of HCM in 11 of 14 G+ relatives with age ≥50 years. Overall, 20.3% of all variant carriers developed one of the predefined cardiac outcomes after a median follow-up of 5.5 years with an average age of 50 (±21) years.

Conclusion

A Belgian founder variant, an exon 23-26 deletion in MYBPC3, was identified in 24 probands and 37 family members. The variant is characterized by a high penetrance of 78.6% at the age of 50 years but has variable phenotypic expression. Adverse outcomes were observed in 20.3% of patients during follow-up.

Circulating Acylcarnitines Associated with Hypertrophic Cardiomyopathy Severity: an Exploratory Cross-Sectional Study in MYBPC3 Founder Variant Carriers

Hypertrophic cardiomyopathy (HCM) is a relatively common genetic heart disease characterised by myocardial hypertrophy. HCM can cause outflow tract obstruction, sudden cardiac death and heart failure, but severity is highly variable. In this exploratory cross-sectional study, circulating acylcarnitines were assessed as potential biomarkers in 124 MYBPC3 founder variant carriers (59 with severe HCM, 26 with mild HCM and 39 phenotype-negative [G + P-]). Elastic net logistic regression identified eight acylcarnitines associated with HCM severity. C3, C4, C6-DC, C8:1, C16, C18 and C18:2 were significantly increased in severe HCM compared to G + P-, and C3, C6-DC, C8:1 and C18 in mild HCM compared to G + P-. In multivariable linear regression, C6-DC and C8:1 correlated to log-transformed maximum wall thickness (coefficient 5.01, p = 0.005 and coefficient 0.803, p = 0.007, respectively), and C6-DC to log-transformed ejection fraction (coefficient -2.50, p = 0.004). Acylcarnitines seem promising biomarkers for HCM severity, however prospective studies are required to determine their prognostic value.

Hypertrophic Cardiomyopathy in Underrepresented Populations: Clinical and Genetic Landscape Based on a Russian Single-Center Cohort Study

Hypertrophic cardiomyopathy (HCM) is a common inherited cardiac disorder characterized by marked clinical and genetic heterogeneity. Ethnic groups underrepresented in studies may have distinctive characteristics. We sought to evaluate the clinical and genetic landscape of Russian HCM patients. A total of 193 patients (52% male; 95% Eastern Slavic origin; median age 56 years) were clinically evaluated, including genetic testing, and prospectively followed to document outcomes. As a result, 48% had obstructive HCM, 25% had HCM in family, 21% were asymptomatic, and 68% had comorbidities. During 2.8 years of follow-up, the all-cause mortality rate was 2.86%/year. A total of 5.7% received an implantable cardioverter-defibrillator (ICD), and 21% had septal reduction therapy. A sequencing analysis of 176 probands identified 64 causative variants in 66 patients (38%); recurrent variants were MYBPC3 p.Q1233* (8), MYBPC3 p.R346H (2), MYH7 p.A729P (2), TPM1 p.Q210R (3), and FLNC p.H1834Y (2); 10 were multiple variant carriers (5.7%); 5 had non-sarcomeric HCM, ALPK3, TRIM63, and FLNC. Thin filament variant carriers had a worse prognosis for heart failure (HR = 7.9, p = 0.007). In conclusion, in the Russian HCM population, the low use of ICD and relatively high mortality should be noted by clinicians; some distinct recurrent variants are suspected to have a founder effect; and family studies on some rare variants enriched worldwide knowledge in HCM.

Untargeted Metabolomics Identifies Potential Hypertrophic Cardiomyopathy Biomarkers in Carriers of MYBPC3 Founder Variants

Hypertrophic cardiomyopathy (HCM) is the most prevalent monogenic heart disease, commonly caused by pathogenic MYBPC3 variants, and a significant cause of sudden cardiac death. Severity is highly variable, with incomplete penetrance among genotype-positive family members. Previous studies demonstrated metabolic changes in HCM. We aimed to identify metabolite profiles associated with disease severity in carriers of MYBPC3 founder variants using direct-infusion high-resolution mass spectrometry in plasma of 30 carriers with a severe phenotype (maximum wall thickness ≥20 mm, septal reduction therapy, congestive heart failure, left ventricular ejection fraction <50%, or malignant ventricular arrhythmia) and 30 age- and sex-matched carriers with no or a mild phenotype. Of the top 25 mass spectrometry peaks selected by sparse partial least squares discriminant analysis, XGBoost gradient boosted trees, and Lasso logistic regression (42 total), 36 associated with severe HCM at a p < 0.05, 20 at p < 0.01, and 3 at p < 0.001. These peaks could be clustered to several metabolic pathways, including acylcarnitine, histidine, lysine, purine and steroid hormone metabolism, and proteolysis. In conclusion, this exploratory case-control study identified metabolites associated with severe phenotypes in MYBPC3 founder variant carriers. Future studies should assess whether these biomarkers contribute to HCM pathogenesis and evaluate their contribution to risk stratification.

Different Phenotypes in Monozygotic Twins, Carriers of the Same Pathogenic Variant for Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a monogenic disease with autosomal dominant inheritance. Genotype−phenotype relationships are complex, with variable penetrance even within the same family. The involvement of other modulating genetic and environmental factors is unknown. We aimed to analyze the HCM in monozygotic twins, carriers of the same founder pathogenic variant MYBPC3 p.G263*. The relationship was verified using the PowerPlex 16 HS System kit. Phenotypic differences and environmental differences (overloading conditions, coexistence and location, lifestyle, sport, and intensity) were analyzed. Three pairs of twins genetically identical for all markers and carriers of MYBPC3 G263* were identified. No environmental differences were identified. One of the 89-year-old twins had symptomatic severe obstructive HCM that required septal ablation, while her twin has remained asymptomatic with mild phenotype >80 years. A 49-year-old twin had a severe phenotype of obstructive HCM and pending myectomy, while his twin had a mild asymptomatic phenotype. In the last pair of twins, one presented a much larger left ventricular hypertrophy than his identical twin. In summary, we present three pairs of HCM twin patients sharing not only the genetic cause of the inherited disease but the entire genetic background. Despite identical genetic information and the absence of other known clinical, environmental, or lifestyle differences, the severity of the HCM phenotype is strikingly different. These unexplained differences should prompt the study of other unknown modulating factors, either epigenetic or environmental.

Molecular genetics in 4 408 cardiomyopathy probands and 3 008 relatives in Norway: 17 years of genetic testing in a national laboratory

Whenever a patient presents with cardiomyopathy, it is important to determine the underlying cause in order to provide the best possible follow-up and treatment. Determining an underlying genetic cause of the disease is also important in order to provide family testing and follow-up of relatives at risk. Unit for Cardiac and Cardiovascular Genetics at Oslo University Hospital has been a national laboratory for genetic testing for cardiomyopathies in Norway since 2003. Data from 4408 probands and 3008 relatives were available. Three probands had two variants, nine had incidental findings of variants not related to their cardiomyopathy diagnosis. Of the remaining 4396 probands, 65.1% were male, age at genetic testing was 50.9 (±18.1) years and 6.1% were under the age of 18. A likely pathogenic or pathogenic variant (216 different variants including 67 novel) was detected in 574 probands. Of the 3008 relatives, 47.6% were male, age at genetic testing was 39.3 (±20.5) years, 17.9% were under the age of 18, and 43.2% were positive for the variant found in their family. Probands and relatives combined, 1/2809 persons in Norway were found to be heterozygous for a cardiomyopathy variant. Next Generation Sequencing provided more findings in dilated cardiomyopathy, especially in TTN. Otherwise, the majority of variants were found in the classical sarcomeric and desmosomal genes. In conclusion, genetic testing provided a genetic basis of the cardiomyopathy in 13.1% of probands, and subsequent family testing identified almost three times as many variant-positive relatives which could be offered preventive follow-up.

The Genetic Architecture of Hypertrophic Cardiomyopathy in Hungary: Analysis of 242 Patients with a Panel of 98 Genes

Hypertrophic cardiomyopathy (HCM) is a primary disease of the myocardium most commonly caused by mutations in sarcomeric genes. We aimed to perform a nationwide large-scale genetic analysis of a previously unreported, representative HCM cohort in Hungary. A total of 242 consecutive HCM index patients (127 men, 44 ± 11 years) were studied with next generation sequencing using a custom-designed gene-panel comprising 98 cardiomyopathy-related genes. A total of 90 patients (37%) carried pathogenic/likely pathogenic (P/LP) variants. The percentage of patients with P/LP variants in genes with definitive evidence for HCM association was 93%. Most of the patients with P/LP variants had mutations in MYBPC3 (55 pts, 61%) and in MYH7 (21 pts, 23%). Double P/LP variants were present in four patients (1.7%). P/LP variants in other genes could be detected in ≤3% of patients. Of the patients without P/LP variants, 46 patients (19%) carried a variant of unknown significance. Non-HCM P/LP variants were identified in six patients (2.5%), with two in RAF1 (p.Leu633Val, p.Ser257Leu) and one in DES (p.Arg406Trp), FHL1 (p.Glu96Ter), TTN (p.Lys23480fs), and in the mitochondrial genome (m.3243A>G). Frameshift, nonsense, and splice-variants made up 82% of all P/LP MYBPC3 variants. In all the other genes, missense mutations were the dominant form of variants. The MYBPC3 p.Gln1233Ter, the MYBPC3 p.Pro955ArgfsTer95, and the MYBPC3 p.Ser593ProfsTer11 variants were identified in 12, 7, and 13 patients, respectively. These three variants made up 36% of all patients with identified P/LP variants, raising the possibility of a possible founder effect for these mutations. Similar to other HCM populations, the MYBPC3 and the MYH7 genes seemed to be the most frequently affected genes in Hungarian HCM patients. The high prevalence of three MYBPC3 mutations raises the possibility of a founder effect in our HCM cohort.

Epidemiology and risk factors of sudden cardiac arrest

PURPOSE OF REVIEW

Sudden cardiac arrest (SCA) remains a major health burden around the globe, most often occurring in the community (out-of-hospital cardiac arrest [OHCA]). SCA accounts for 15-20% of all natural deaths in adults in the USA and Western Europe, and up to 50% of all cardiovascular deaths. To reduce this burden, more knowledge is needed about its key facets such as its incidence in various geographies, its risk factors, and the populations that may be at risk.

RECENT FINDINGS

SCA results from a complex interaction of inherited and acquired causes, specific to each individual. Resolving this complexity, and designing personalized prevention and treatment, requires an integrated approach in which big datasets that contain all relevant factors are collected, and a multimodal analysis. Such datasets derive from multiple data sources, including all players in the chain-of-care for OHCA. This recognition has led to recently started large-scale collaborative efforts in Europe.

SUMMARY

Our insights into the causes of SCA are steadily increasing thanks to the creation of big datasets dedicated to SCA research. These insights may be used to earlier recognize of individuals at risk, the design of personalized methods for prevention, and more effective resuscitation strategies for OHCA.

Founder mutation in myosin-binding protein C with an early onset and a high penetrance in males

OBJECTIVE

One of the challenges in hypertrophic cardiomyopathy (HCM) is to determine the pathogenicity of genetic variants and to establish genotype/phenotype correlations. This study aimed to: (1) demonstrate that MYBPC3 c.2149-1G>A is a founder pathogenic variant, (2) describe the phenotype and clinical characteristics of mutation carriers and (3) compare these patients with those with the most frequent pathogenic HCM variants: MYBPC3 p.Arg502Trp/Gln.

METHODS

We reviewed genetic tests performed in HCM probands at our institution. We carried out transcript analyses to demonstrate the splicing effect, and haplotype analyses to support the founder effect of MYBPC3 c.2149-1G>A. Carriers with this mutation were compared with those from MYBPC3 p.Arg502Trp/Gln in terms of presentation features, imaging and outcomes.

RESULTS

MYBPC3 c.2149-1G>A was identified in 8 of 570 probands and 25 relatives. Penetrance was age and sex dependent, 50.0% of the carriers over age 36 years and 75.0% of the carriers over 40 years showing HCM. Penetrance was significantly higher in males: in carriers older than 30 years old, 100.0% of males vs 50.0% of females had a HCM phenotype (p=0.01). Males were also younger at diagnosis (32±13 vs 53±10 years old, p<0.001). MYBPC3 c.2149-1G>A resulted in an abnormal transcript that led to haploinsufficiency and was segregated in two haplotypes. However, both came from one founder haplotype. Affected carriers showed a better functional class and higher left ventricular ejection fraction (LVEF) than patients with MYBPC3 p.Arg502Trp/Gln (p<0.05 for both). Nevertheless, the rate of major adverse outcomes was similar between the two groups.

CONCLUSIONS

MYBPC3 c.2149-1G>A splicing variant is a founder mutation. Affected males show an early onset of HCM and with higher penetrance than women. Carriers show better functional class and higher LVEF than MYBPC3 p.Arg502Trp/Gln carriers, but a similar rate of major adverse outcomes.

Myocardial Deformation Analysis in MYBPC3 and MYH7 Related Sarcomeric Hypertrophic Cardiomyopathy-The Graz Hypertrophic Cardiomyopathy Registry

Accumulating evidence suggests that individuals with sarcomeric hypertrophic cardiomyopathy (HCM) carrying MYH7 mutations may have a worse prognosis than MYBPC3 mutation carriers. Myocardial deformation analysis is superior to standard echocardiography in detecting subtle myocardial dysfunction and scar formation, but studies evaluating the association with HCM genotype are scarce. We therefore aimed to compare myocardial strain parameters between MYBPC3 and MYH7 mutation carriers with proven HCM. Participants of the prospective Graz HCM Registry carrying at least one causative mutation in MYBPC3 (n = 39) or MYH7 (n = 18) were enrolled. MYBPC3 mutation carriers were older, predominantly male and more often treated with an implantable cardioverter-defibrillator (39% vs. 0%; p = 0.002). Using analyses of covariance, there were no significant differences between MYBPC3 and MYH7 mutation carriers with regard to left ventricular global longitudinal strain (estimated marginal means ± standard deviation: −16.9 ± 0.6% vs. −17.3 ± 0.9%; p = 0.807) and right ventricular 6-segments endocardial strain (−24.3 ± 1.0% vs. 26.3 ± 1.5%; p = 0.285). Our study suggests, that myocardial deformation analysis may not be helpful in concluding on the underlying HCM genotype, and vice versa.

Clinical characterization of the first Belgian SCN5A founder mutation cohort

AIMS

We identified the first Belgian SCN5A founder mutation, c.4813 + 3_4813 + 6dupGGGT. To describe the clinical spectrum and disease severity associated with this mutation, clinical data of 101 SCN5A founder mutation carriers and 46 non-mutation carrying family members from 25 Belgian families were collected.

METHODS AND RESULTS

The SCN5A founder mutation was confirmed by haplotype analysis. The clinical history and electrocardiographic parameters of the mutation carriers and their family members were gathered and compared. A cardiac electrical abnormality was observed in the majority (82%) of the mutation carriers. Cardiac conduction defects, defined as PR or QRS prolongation on electrocardiogram (ECG), were most frequent, occurring in 65% of the mutation carriers. Brugada syndrome (BrS) was the second most prevalent phenotype identified in 52%, followed by atrial dysrythmia in 11%. Overall, 33% of tested mutation carriers had a normal sodium channel blocker test. Negative tests were more common in family members distantly related to the proband. Overall, 23% of the mutation carriers were symptomatic, with 8% displaying major adverse events. As many as 13% of the patients tested with a sodium blocker developed ventricular arrhythmia. One family member who did not carry the founder mutation was diagnosed with BrS.

CONCLUSION

The high prevalence of symptoms and sensitivity to sodium channel blockers in our founder population highlights the adverse effect of the founder mutation on cardiac conduction. The large phenotypical heterogeneity, variable penetrance, and even non-segregation suggest that other genetic (and environmental) factors modify the disease expression, severity, and outcome in these families.

Generation of bi-allelic MYBPC3 truncating mutant and isogenic control from an iPSC line of a patient with hypertrophic cardiomyopathy

MYBPC3 is the most frequently affected gene in hypertrophic cardiomyopathy (HCM), which is an autosomal-dominant cardiac disease caused by mutations in sarcomeric proteins. Bi-allelic truncating MYBPC3 mutations are associated with severe forms of neonatal cardiomyopathy. We reprogrammed skin fibroblasts from a HCM patient carrying a heterozygous MYBPC3 truncating mutation into human induced pluripotent stem cells (iPSC) and used CRISPR/Cas9 to generate bi-allelic MYBPC3 truncating mutation and isogenic control hiPSC lines. All lines expressed pluripotency markers, had normal karyotype and differentiated into endoderm, ectoderm and cardiomyocytes in vitro. This set of three lines provides a useful tool to study HCM pathomechanisms.

Diagnostic yield of targeted next generation sequencing in 2002 Dutch cardiomyopathy patients

BACKGROUND

Next-generation sequencing (NGS) is increasingly used for clinical evaluation of cardiomyopathy patients as it allows for simultaneous screening of multiple cardiomyopathy-associated genes. Adding copy number variant (CNV) analysis of NGS data is not routine yet and may contribute to the diagnostic yield.

OBJECTIVES

Determine the diagnostic yield of our targeted NGS gene panel in routine clinical diagnostics of Dutch cardiomyopathy patients and explore the impact of exon CNVs on diagnostic yield.

METHODS

Patients (N = 2002) referred for clinical genetic analysis underwent diagnostic testing of 55-61 genes associated with cardiomyopathies. Samples were analyzed and evaluated for single nucleotide variants (SNVs), indels and CNVs. CNVs identified in the NGS data and suspected of being pathogenic based on type, size and location were confirmed by additional molecular tests.

RESULTS

A (likely) pathogenic (L)P variant was detected in 22.7% of patients, including 3 with CNVs and 25 where a variant was identified in a gene currently not associated with the patient's cardiomyopathy subtype. Only 15 out of 2002 patients (0.8%) were found to carry two (L)P variants.

CONCLUSION

The yield of routine clinical diagnostics of cardiomyopathies was relatively low when compared to literature. This is likely due to the fact that our study reports the outcome of patients in daily routine diagnostics, therefore also including patients not fully fulfilling (subtype specific) cardiomyopathy criteria. This may also explain why (L)P variants were identified in genes not associated with the reported subtype. The added value of CNV analysis was shown to be limited but not negligible.

BIO FOr CARE: biomarkers of hypertrophic cardiomyopathy development and progression in carriers of Dutch founder truncating MYBPC3 variants-design and status

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most prevalent monogenic heart disease, commonly caused by truncating variants in the MYBPC3 gene. HCM is an important cause of sudden cardiac death; however, overall prognosis is good and penetrance in genotype-positive individuals is incomplete. The underlying mechanisms are poorly understood and risk stratification remains limited.

AIM

To create a nationwide cohort of carriers of truncating MYBPC3 variants for identification of predictive biomarkers for HCM development and progression.

METHODS

In the multicentre, observational BIO FOr CARe (Identification of BIOmarkers of hypertrophic cardiomyopathy development and progression in Dutch MYBPC3 FOunder variant CARriers) cohort, carriers of the c.2373dupG, c.2827C > T, c.2864_2865delCT and c.3776delA MYBPC3 variants are included and prospectively undergo longitudinal blood collection. Clinical data are collected from first presentation onwards. The primary outcome constitutes a composite endpoint of HCM progression (maximum wall thickness ≥ 20 mm, septal reduction therapy, heart failure occurrence, sustained ventricular arrhythmia and sudden cardiac death).

RESULTS

So far, 250 subjects (median age 54.9 years (interquartile range 43.3, 66.6), 54.8% male) have been included. HCM was diagnosed in 169 subjects and dilated cardiomyopathy in 4. The primary outcome was met in 115 subjects. Blood samples were collected from 131 subjects.

CONCLUSION

BIO FOr CARe is a genetically homogeneous, phenotypically heterogeneous cohort incorporating a clinical data registry and longitudinal blood collection. This provides a unique opportunity to study biomarkers for HCM development and prognosis. The established infrastructure can be extended to study other genetic variants. Other centres are invited to join our consortium.

Targeting the population for gene therapy with MYBPC3

Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited myocardial disease characterized by unexplained left ventricular hypertrophy, diastolic dysfunction and myocardial disarray. Clinical heterogeneity is wide, ranging from asymptomatic individuals to heart failure, arrhythmias and sudden death. HCM is often caused by mutations in genes encoding components of the sarcomere. Among them, MYBPC3, encoding cardiac myosin-myosin binding protein C is the most frequently mutated gene. Three quarter of pathogenic or likely pathogenic mutations in MYBPC3 are truncating and the resulting protein was not detected in HCM myectomy samples. The overall prognosis of the patients is excellent if managed with contemporary therapy, but still remains a significant disease-related health burden, and carriers with double heterozygous, compound heterozygous and homozygous mutations often display a more severe clinical phenotype than single heterozygotes. We propose these individuals as a good target population for MYBPC3 gene therapy.

MYBPC3 Haplotype Linked to Hypertrophic Cardiomyopathy in Rhesus Macaques (Macaca mulatta)

In humans, abnormal thickening of the left ventricle of the heart clinically defines hypertrophic cardiomyopathy (HCM), a common inherited cardiovascular disorder that can precede a sudden cardiac death event. The wide range of clinical presentations in HCM obscures genetic variants that may influence an individual's susceptibility to sudden cardiac death. Although exon sequencing of major sarcomere genes can be used to detect high-impact causal mutations, this strategy is successful in only half of patient cases. The incidence of left ventricular hypertrophy (LVH) in a managed research colony of rhesus macaques provides an excellent comparative model in which to explore the genomic etiology of severe HCM and sudden cardiac death. Because no rhesus HCM-associated mutations have been reported, we used a next-generation genotyping assay that targets 7 sarcomeric rhesus genes within 63 genomic sites that are orthologous to human genomic regions known to harbor HCM disease variants. Amplicon sequencing was performed on 52 macaques with confirmed LVH and 42 unrelated, unaffected animals representing both the Indian and Chinese rhesus macaque subspecies. Bias-reduced logistic regression uncovered a risk haplotype in the rhesus MYBPC3 gene, which is frequently disrupted in both human and feline HCM; this haplotype implicates an intronic variant strongly associated with disease in either homozygous or carrier form. Our results highlight that leveraging evolutionary genomic data provides a unique, practical strategy for minimizing population bias in complex disease studies.

Cardiogenetics, 25 years a growing subspecialism

The cardiology and clinical genetics subspecialty of cardiogenetics has experienced a tremendous growth in the past 25 years. This review discusses examples of the progress that has been made as well as new challenges that have arisen within this field, with special focus on the Netherlands. A significant number of Dutch founder mutations, i.e. mutations shared by a number of individuals who have a common origin and all share a unique chromosomal background on which the mutation occurred, have been identified and have provided unique insights into genotype-phenotype correlations in inherited arrhythmia syndromes and inherited cardiomyopathies.

Cardiological and genetic screening of family members of young victims of sudden cardiac death combined with genetic testing in the deceased individual have turned out to be rewarding. However, the interpretation of the results of genetic testing in this setting and in the setting of living patients with a (suspected) phenotype is now considered more challenging than previously anticipated, because the introduction of high-throughput sequencing technologies has resulted in the identification of a significant number of variants of unknown significance. Interpretation of genetic and clinical findings by experienced multidisciplinary teams are key to ensure a high quality of care to the patient and the family.

Hypertrophic cardiomyopathy in myosin-binding protein C (MYBPC3) Icelandic founder mutation carriers

Objective

The myosin-binding protein C (MYBPC3) c.927-2A>G founder mutation accounts for >90% of sarcomeric hypertrophic cardiomyopathy (HCM) in Iceland. This cross-sectional observational study explored the penetrance and phenotypic burden among carriers of this single, prevalent founder mutation.

Methods

We studied 60 probands with HCM caused by MYBPC3 c.927-2A>G and 225 first-degree relatives. All participants underwent comprehensive clinical evaluation and relatives were genotyped.

Results

Genetic and clinical evaluation of relatives identified 49 genotype-positive (G+) relatives with left ventricular hypertrophy (G+/LVH+), 59 G+without LVH (G+/LVH-) and 117 genotype-negative relatives (unaffected). Compared with HCM probands, G+/LVH+ relatives were older at HCM diagnosis, had less LVH, a less prevalent diastolic dysfunction, fewer ECG abnormalities, lower serum N-terminal pro-B-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin I levels, and fewer symptoms. The penetrance of HCM was influenced by age and sex; specifically, LVH was present in 39% of G+males but only 9% of G+females under age 40 years (p=0.015), versus 86% and 83%, respectively, after age 60 (p=0.89). G+/LVH- subjects had normal wall thicknesses, diastolic function and NT-proBNP levels, but subtle changes in LV geometry and more ECG abnormalities than their unaffected relatives.

Conclusions

Phenotypic expression of the Icelandic MYBPC3 founder mutation varies by age, sex and proband status. Men are more likely to have LVH at a younger age, and disease manifestations were more prominent in probands than in relatives identified via family screening. G+/LVH- individuals had subtle clinical differences from unaffected relatives well into adulthood, indicating subclinical phenotypic expression of the pathogenic mutation.

Sex Differences at the Time of Myectomy in Hypertrophic Cardiomyopathy

BACKGROUND

One of the first clinically detectable alterations in heart function in hypertrophic cardiomyopathy (HCM) is a decline in diastolic function. Diastolic dysfunction is caused by changes in intrinsic properties of cardiomyocytes or an increase in fibrosis. We investigated whether clinical and cellular parameters of diastolic function are different between male and female patients with HCM at the time of myectomy.

METHODS AND RESULTS

Cardiac tissue from the interventricular septum of patients with HCM (27 women and 44 men) was obtained during myectomy preceded by echocardiography. At myectomy, female patients were 7 years older than male patients and showed more advanced diastolic dysfunction than men evident from significantly higher values for E/e' ratio, left ventricular filling pattern, tricuspid regurgitation velocity, and left atrial diameter indexed for body surface. Whereas most male patients (56%) showed mild (grade I) diastolic dysfunction, 50% of female patients showed grade III diastolic dysfunction. Passive tension in HCM cardiomyocytes was comparable with controls, and myofilament calcium sensitivity was higher in HCM compared with controls, but no sex differences were observed in myofilament function. In female patients with HCM, titin was more compliant, and more fibrosis was present compared with men. Differences between female and male patients with HCM remained significant after correction for age.

CONCLUSIONS

Female patients with HCM are older at the time of myectomy and show greater impairment of diastolic function. Furthermore, left ventricular and left atrial remodeling is increased in women when corrected for body surface area. At a cellular level, HCM women showed increased compliant titin and a larger degree of interstitial fibrosis.

Insights Into Hypertrophic Cardiomyopathy Evaluation Through Follow-up of a Founder Pathogenic Variant

INTRODUCTION AND OBJECTIVES

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease. The current challenge relies on the accurate classification of the pathogenicity of the variants. Transthoracic echocardiography (TTE) is recommended at initial evaluation and cardiac magnetic resonance (CMR) imaging should also be considered. We aimed to reappraise the penetrance and clinical expression of the MYBPC3 p.G263* variant.

METHODS

Three hundred and eighty-four HCM probands and a control cohort of 450 individuals were studied for the main sarcomere genes by next-generation sequencing. All MYBPC3 p.G263* carriers were identified and family screening was performed. Clinical information was recorded retrospectively before 2015 and prospectively thereafter. Extra effort was invested in performing CMR in all carriers, despite TTE results.

RESULTS

Thirteen HCM probands and none of the controls were carriers of the MYBPC3 p.G263* pathogenic variant (according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology). A total of 39 carriers were identified with family screening. Most patients with HCM were asymptomatic at the time of diagnosis and showed late-onset disease. Despite having a relatively benign course in the young, late HCM-related complications could occur. Penetrance was around 70% when evaluated by TTE and was 87.2% with TTE plus CMR. Penetrance was age-dependent, reaching 100% in carriers older than 55 years.

CONCLUSIONS

MYBPC3 p.G263* shares with most truncating pathogenic variants in this gene a late onset, relatively benign clinical course in the young, and high penetrance. Cardiac magnetic resonance could be a useful tool to evaluate carriers despite TTE results.

Clinical Application of Genetic Testing in Heart Failure

PURPOSE OF REVIEW

The purpose of this review is to present our current understanding of the genetic etiologies that may cause or predispose to heart failure. We highlight known phenotypes for which a genetic evaluation has clinical utility.

RECENT FINDINGS

The literature continues to demonstrate and confirm a genetic basis for conditions that cause heart failure. Evidence suggests a genetic model involving rare and common variants of strong or weak effect, in combination with environmental factors that may manifest as familial or simplex disease. Clinical genetic testing is available for several phenotypes, which can aid in the diagnosis and identification of at-risk family members. The evaluation of heart failure should include investigating etiologies with a genetic basis. Conducting a genetic evaluation in patients with heart failure requires the ability to identify possible genetic etiologies in an individual's phenotype, obtain relevant family history, and clinically interpret genetic testing results.

Clinical Characteristics and Long-Term Outcome of Hypertrophic Cardiomyopathy in Individuals With a MYBPC3 (Myosin-Binding Protein C) Founder Mutation

BACKGROUND

MYBPC3 (Myosin-binding protein C) founder mutations account for 35% of hypertrophic cardiomyopathy (HCM) cases in the Netherlands. We compared clinical characteristics and outcome of MYBPC3 founder mutation (FG+) HCM with nonfounder genotype-positive (G+) and genotype-negative (G-) HCM.

METHODS AND RESULTS

The study included 680 subjects: 271 FG+ carriers, 132 G+ probands with HCM, and 277 G- probands with HCM. FG+ carriers included 134 FG+ probands with HCM, 54 FG+ relatives diagnosed with HCM after family screening, 74 FG+/phenotype-negative relatives, and 9 with noncompaction or dilated cardiomyopathy. The clinical phenotype of FG+ and G+ probands with HCM was similar. FG+ and G+ probands were younger with less left ventricular outflow tract obstruction than G- probands, however, had more hypertrophy, and nonsustained ventricular tachycardia. FG+ relatives with HCM had less hypertrophy, smaller left atria, and less systolic and diastolic dysfunction than FG+ probands with HCM. After 8±6 years, cardiovascular mortality in FG+ probands with HCM was similar to G+ HCM (22% versus 14%; log-rank P=0.14), but higher than G- HCM (22% versus 6%; log-rank P<0.001) and FG+ relatives with HCM (22% versus 4%; P=0.009). Cardiac events were absent in FG+/phenotype-negative relatives; subtle HCM developed in 11% during 6 years of follow-up.

CONCLUSIONS

Clinical phenotype and outcome of FG+ HCM was similar to G+ HCM but worse than G- HCM and FG+ HCM diagnosed in the context of family screening. These findings indicate the need for more intensive follow-up of FG+ and G+ HCM versus G- HCM and FG+ HCM in relatives.

Penetrance of Hypertrophic Cardiomyopathy in Children Who Are Mutation Positive

OBJECTIVES

To investigate the presence of hypertrophic cardiomyopathy (HCM) at first cardiac evaluation and during follow-up and cardiac events in predictively tested children who are mutation positive.

STUDY DESIGN

The study included 119 predictively tested children who were mutation positive, with a mean age of 12.1 years. A family history and clinical variables from all cardiac evaluations after predictive genetic testing were recorded. Outcome measures were a clinical diagnosis of HCM, death, and cardiac events.

RESULTS

No child died during a mean follow-up of 6.9 ± 3.8 years: 95 children were evaluated more than once. Eight (6.7%) children who were mutation positive were diagnosed with HCM at one or more cardiac evaluation(s), some with severe hypertrophy. In one patient who fulfilled the diagnostic criteria for HCM a cardiac event occurred during follow-up. She received an appropriate implantable cardioverter-defibrillator shock 4 years after a prophylactic implantable cardioverter-defibrillator was implanted.

CONCLUSION

The risk for predictively tested children who are mutation positive to develop HCM during childhood and the risk of cardiac events in children who are phenotype negative are low. In children who are phenotype positive, however, severe hypertrophy and cardiac events can develop. Further research is necessary to study whether the interval between cardiac evaluations in children can be increased after a normal first evaluation and whether risk stratification for sudden cardiac death is necessary in children who are phenotype negative.

Transthyretin amyloidosis: a phenocopy of hypertrophic cardiomyopathy

OBJECTIVES

Hypertrophic cardiomyopathy (HCM) is an inherited cardiac disorder that affects over one in 500 persons worldwide. The autosomal dominant transmission of HCM implies that many relatives are at risk for HCM associated morbidity and mortality, therefore genetic testing and counselling is of great importance. However, in only 50-60% of the patients a mutation is found, which hampers predictive genetic testing in relatives. In HCM patients in whom the causal mutation has not been identified (yet), phenocopies of HCM - i.e. diseases that mimic HCM - could be responsible for the HCM phenotype. One of the HCM phenocopies is transthyretin amyloidosis (ATTR), caused by mutations in the transthyretin (TTR) gene.

METHODS

From 697 HCM index patients referred to our cardiogenetics outpatient clinic and tested for HCM associated genes between January 1997 and December 2012, we selected the ones without a detected causal mutation (n = 345). In these patients, additional DNA analysis of the TTR gene was performed.

RESULTS

In four patients (1.2%), a TTR mutation was detected (E7G, V30M, T119M, V122I). The E7G mutation is probably a non-pathogenic mutation. The T119M mutation is a known TTR mutation, but does not cause a cardiac phenotype. So in two (0.6%) patients, TTR analysis identified the cause of their HCM.

CONCLUSIONS

ATTR should always be considered in patients with unexplained HCM, especially because of the great benefit of an early diagnosis regarding treatment and prognosis.

Life-long tailoring of management for patients with hypertrophic cardiomyopathy : Awareness and decision-making in changing scenarios

Hypertrophic cardiomyopathy (HCM) is the most common genetic heart disease, characterised by complex pathophysiology and extensive genetic and clinical heterogeneity. In most patients, HCM is caused by mutations in cardiac sarcomere protein genes and inherited as an autosomal dominant trait. The clinical phenotype ranges from severe presentations at a young age to lack of left ventricular hypertrophy in genotype-positive individuals. No preventative treatment is available as the sequence and causality of the pathomechanisms that initiate and exacerbate HCM are unknown. Sudden cardiac death and end-stage heart failure are devastating expressions of this disease. Contemporary management including surgical myectomy and implantable cardiac defibrillators has shown significant impact on long-term prognosis. However, timely recognition of specific scenarios - including transition to the end-stage phase - may be challenging due to limited awareness of the progression patterns of HCM. This in turn may lead to missed therapeutic opportunities. To illustrate these difficulties, we describe two HCM patients who progressed from the typical hyperdynamic stage of asymmetric septal thickening to end-stage heart failure with severely reduced ejection fraction. We highlight the different stages of this complex inherited cardiomyopathy based on the clinical staging proposed by Olivotto and colleagues. In this way, we aim to provide a practical guide for clinicians and hope to increase awareness for this common form of cardiac disease.

Management of pregnancy in cardiomyopathies and heart failure

Pregnancy exposes women with inherited cardiomyopathies to increased risk for arrhythmias and heart failure. In asymptomatic patients with inherited cardiomyopathies, pregnancy is generally well tolerated. Preconception evaluation, risk assessment and proper counseling by a team of experienced physicians are mandatory in managing women with inherited cardiomyopathies planning pregnancy. In this paper, we reviewed the clinical course, risk assessment and management during pregnancy of women with cardiomyopathies.

The genetic basis of hypertrophic cardiomyopathy in cats and humans

Mutations in genes that encode for muscle sarcomeric proteins have been identified in humans and two breeds of domestic cats with hypertrophic cardiomyopathy (HCM). This article reviews the history, genetics, and pathogenesis of HCM in the two species in order to give veterinarians a perspective on the genetics of HCM. Hypertrophic cardiomyopathy in people is a genetic disease that has been called a disease of the sarcomere because the preponderance of mutations identified that cause HCM are in genes that encode for sarcomeric proteins (Maron and Maron, 2013). Sarcomeres are the basic contractile units of muscle and thus sarcomeric proteins are responsible for the strength, speed, and extent of muscle contraction. In people with HCM, the two most common genes affected by HCM mutations are the myosin heavy chain gene (MYH7), the gene that encodes for the motor protein β-myosin heavy chain (the sarcomeric protein that splits ATP to generate force), and the cardiac myosin binding protein-C gene (MYBPC3), a gene that encodes for the closely related structural and regulatory protein, cardiac myosin binding protein-C (cMyBP-C). To date, the two mutations linked to HCM in domestic cats (one each in Maine Coon and Ragdoll breeds) also occur in MYBPC3 (Meurs et al., 2005, 2007). This is a review of the genetics of HCM in both humans and domestic cats that focuses on the aspects of human genetics that are germane to veterinarians and on all aspects of feline HCM genetics.

Value of Genetic Testing for the Prediction of Long-Term Outcome in Patients With Hypertrophic Cardiomyopathy

Pathogenic gene mutations are found in about 50% of patients with hypertrophic cardiomyopathy (HC). Previous studies have shown an association between sarcomere mutations and medium-term outcome. The association with long-term outcome has not been described. The aim of this cohort study was to assess the long-term outcomes of patients with genotype positive (G+) and genotype negative (G-) HC. The study population consisted of 626 patients with HC (512 probands and 114 relatives) who underwent phenotyping and genetic testing from 1985 to 2014. End points were all-cause mortality, cardiovascular (CV) mortality, heart failure (HF)-related mortality, and sudden cardiac death/aborted sudden cardiac death (SCD/aborted SCD). Kaplan-Meier and multivariate Cox regression analyses were performed. A pathogenic mutation was detected in 327 patients (52%). G+ probands were younger than G- probands (46 ± 15 vs 55 ± 15 years, p <0.001), had more non sustained ventricular tachycardia (34% vs 13%; p <0.001), more often a history of syncope (14% vs 7%; p = 0.016), and more extreme hypertrophy (maximal wall thickness ≥30 mm, 7% vs 1%; p <0.001). G- probands were more symptomatic (New York Heart Association ≥II, 73% vs 53%, p <0.001) and had higher left ventricular outflow tract gradients (42 ± 39 vs 29 ± 33 mm Hg, p = 0.001). During 12 ± 9 years of follow-up, G+ status was an independent risk factor for all-cause mortality (hazard ratio [HR] 1.90, 95% CI 1.14 to 3.15; p = 0.014), CV mortality (HR 2.82, 95% CI 1.49 to 5.36; p = 0.002), HF-related mortality (HR 6.33, 95% CI 1.79 to 22.41; p = 0.004), and SCD/aborted SCD (HR 2.88, 95% CI 1.23 to 6.71; p = 0.015). In conclusion, during long-term follow-up, patients with G+ HC are at increased risk of all-cause death, CV death, HF-related death, and SCD/aborted SCD.

Comparison of the effects of a truncating and a missense MYBPC3 mutation on contractile parameters of engineered heart tissue

Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by left ventricular hypertrophy, diastolic dysfunction and myocardial disarray. The most frequently mutated gene is MYBPC3, encoding cardiac myosin-binding protein-C (cMyBP-C). We compared the pathomechanisms of a truncating mutation (c.2373_2374insG) and a missense mutation (c.1591G>C) in MYBPC3 in engineered heart tissue (EHT). EHTs enable to study the direct effects of mutants without interference of secondary disease-related changes. EHTs were generated from Mybpc3-targeted knock-out (KO) and wild-type (WT) mouse cardiac cells. MYBPC3 WT and mutants were expressed in KO EHTs via adeno-associated virus. KO EHTs displayed higher maximal force and sensitivity to external [Ca(2+)] than WT EHTs. Expression of WT-Mybpc3 at MOI-100 resulted in ~73% cMyBP-C level but did not prevent the KO phenotype, whereas MOI-300 resulted in ≥95% cMyBP-C level and prevented the KO phenotype. Expression of the truncating or missense mutation (MOI-300) or their combination with WT (MOI-150 each), mimicking the homozygous or heterozygous disease state, respectively, failed to restore force to WT level. Immunofluorescence analysis revealed correct incorporation of WT and missense, but not of truncated cMyBP-C in the sarcomere. In conclusion, this study provides evidence in KO EHTs that i) haploinsufficiency affects EHT contractile function if WT cMyBP-C protein levels are ≤73%, ii) missense or truncating mutations, but not WT do not fully restore the disease phenotype and have different pathogenic mechanisms, e.g. sarcomere poisoning for the missense mutation, iii) the direct impact of (newly identified) MYBPC3 gene variants can be evaluated.

Sudden Cardiac Arrest and Rare Genetic Variants in the Community

BACKGROUND

Sudden cardiac arrest (SCA) ranks among the most common causes of death worldwide. Because SCA is most often lethal, yet mostly occurs in individuals without previously known cardiac disease, the identification of patients at risk for SCA could save many lives. In unselected SCA victims from the community, common genetic variants (which are not disease-causing per se, but may increase susceptibility to ventricular fibrillation) are found to be associated with increased SCA risk. However, whether rare genetic variants contribute to SCA risk in the community is largely unexplored.

METHODS AND RESULTS

We here investigated the involvement of rare genetic variants in SCA risk at the population level by studying the prevalence of 6 founder genetic variants present in the Dutch population (PLN-p.Arg14del, MYBPC3-p.Trp792fsX17, MYBPC3-p.Arg943X, MYBPC3-p.Pro955fsX95, PKP2-p.Arg79X, and the Chr7q36 idiopathic ventricular fibrillation risk haplotype) in a cohort of 1440 unselected Dutch SCA victims included in the Amsterdam Resuscitation Study (ARREST). The six studied founder mutations were found to be more prevalent (1.1%) in the ARREST SCA cohort compared with an ethnically and geographically matched set of controls (0.4%, n=1379; P<0.05) or a set of Dutch individuals drawn from the Genome of the Netherlands (GoNL) study (0%, n=500; P<0.02).

CONCLUSIONS

This finding provides proof-of-concept for the notion that rare genetic variants contribute to some extent to SCA risk in the community.

Hypertrophic remodelling in cardiac regulatory myosin light chain (MYL2) founder mutation carriers

AIMS

Phenotypic heterogeneity and incomplete penetrance are common in patients with hypertrophic cardiomyopathy (HCM). We aim to improve the understanding in genotype-phenotype correlations in HCM, particularly the contribution of an MYL2 founder mutation and risk factors to left ventricular hypertrophic remodelling.

METHODS AND RESULTS

We analysed 14 HCM families of whom 38 family members share the MYL2 c.64G > A [p.(Glu22Lys)] mutation and a common founder haplotype. In this unique cohort, we investigated factors influencing phenotypic outcome in addition to the primary mutation. The mutation alone showed benign disease manifestation with low penetrance. The co-presence of additional risk factors for hypertrophy such as hypertension, obesity, or other sarcomeric gene mutation increased disease penetrance substantially and caused HCM in 89% of MYL2 mutation carriers (P = 0.0005). The most prominent risk factor was hypertension, observed in 71% of mutation carriers with HCM and an additional risk factor.

CONCLUSION

The MYL2 mutation c.64G > A on its own is incapable of triggering clinical HCM in most carriers. However, the presence of an additional risk factor for hypertrophy, particularly hypertension, adds to the development of HCM. Early diagnosis of risk factors is important for early treatment of MYL2 mutation carriers and close monitoring should be guaranteed in this case. Our findings also suggest that the presence of hypertension or another risk factor for hypertrophy should not be an exclusion criterion for genetic studies.

Cardiac myosin-binding protein C (MYBPC3) in cardiac pathophysiology

More than 350 individual MYPBC3 mutations have been identified in patients with inherited hypertrophic cardiomyopathy (HCM), thus representing 40–50% of all HCM mutations, making it the most frequently mutated gene in HCM. HCM is considered a disease of the sarcomere and is characterized by left ventricular hypertrophy, myocyte disarray and diastolic dysfunction. MYBPC3 encodes for the thick filament associated protein cardiac myosin-binding protein C (cMyBP-C), a signaling node in cardiac myocytes that contributes to the maintenance of sarcomeric structure and regulation of contraction and relaxation. This review aims to provide a succinct overview of how mutations in MYBPC3 are considered to affect the physiological function of cMyBP-C, thus causing the deleterious consequences observed inHCM patients. Importantly, recent advances to causally treat HCM by repairing MYBPC3 mutations by gene therapy are discussed here, providing a promising alternative to heart transplantation for patients with a fatal form of neonatal cardiomyopathy due to bi-allelic truncating MYBPC3 mutations.

Genetics of sudden cardiac death

Sudden cardiac death occurs in a broad spectrum of cardiac pathologies and is an important cause of mortality in the general population. Genetic studies conducted during the past 20 years have markedly illuminated the genetic basis of the inherited cardiac disorders associated with sudden cardiac death. Here, we review the genetic basis of sudden cardiac death with a focus on the current knowledge on the genetics of the primary electric disorders caused primarily by mutations in genes encoding ion channels, and the cardiomyopathies, which have been attributed to mutations in genes encoding a broader category of proteins, including those of the sarcomere, the cytoskeleton, and desmosomes. We discuss the challenges currently faced in unraveling genetic factors that predispose to sudden cardiac death in the setting of sequela of coronary artery disease and present the genome-wide association studies conducted in recent years on electrocardiographic parameters, highlighting their potential in uncovering new biological insights into cardiac electric function.

Toward Personalized Medicine: Does Genetic Diagnosis of Pediatric Cardiomyopathy Influence Patient Management?

A goal of personalized medicine is to provide increasingly sophisticated, individualized approaches to management and therapy for disease. Genetics is the engine that drives personalized medicine, holding the promise of therapeutics directed toward the unique needs of each patient. The 3^rd International Conference on Cardiomyopathy in Children provided a forum to discuss the current status of personalized approaches to diagnosis, management, and therapy in the pediatric cardiomyopathy population. This review will focus on the importance of genetic diagnosis in this population as a necessary first step toward understanding the best approach to management and influencing disease outcome. The genetic heterogeneity of cardiomyopathy in children, the implications of specific genotypes, the ability to risk stratify based on genotype, and the impact on cascade screening in family members will be discussed.

A founder MYBPC3 mutation results in HCM with a high risk of sudden death after the fourth decade of life

BACKGROUND

Mutations in the cardiac myosin binding protein C (MYBPC3) gene account for a significant proportion of patients affected with hypertrophic cardiomyopathy (HCM). The aim of this study was to evaluate the penetrance and the impact of a frequent founder MYBPC3 mutation on HCM clinical expression and prognosis.

METHODS AND RESULTS

Mutation screening of MYBPC3 gene was performed in 97 HCM probands. Nineteen (19.5%) resulted to be carriers of the founder p.F305Pfs*27 mutation and other 45 mutation carriers were identified during the evaluation of 14 families. Eleven (38%) mutation carriers were diagnosed between ages 30 years and 40 years. Disease penetrance was incomplete (64.4%), age-related and was greater in men than women (85% vs 48%, p=0.009). Probands carrying the founder mutation exhibited highest prevalence of non-sustained ventricular tachycardia (63% vs 22%, p=0.003; 63% vs 23%, p=0.01) and implantable cardioverter-defibrillator (58% vs 17%, p=0.001; 58% vs 18%, p=0.005) when compared with probands without MYBPC3 mutations or carrying other MYBPC3 mutations. Reduced survival due to sudden cardiac death (SCD) or aborted SCD occurred more frequently after the fourth decade of life in probands carrying p.F305Pfs*27 mutation than those without MYBPC3 mutations (32% vs 15%, p=0.01).

CONCLUSIONS

p.F305Pfs*27 mutation carriers have a high probability to develop the disease between ages 30 years and 40 years with a significant major risk if they are men. This founder mutation is associated with an increase of SCD/aborted SCD events after the fourth decade of life.These findings are of relevant importance for management and clinical decision-making in patients with HCM.

Compound heterozygous or homozygous truncating MYBPC3 mutations cause lethal cardiomyopathy with features of noncompaction and septal defects

Familial hypertrophic cardiomyopathy (HCM) is usually caused by autosomal dominant pathogenic mutations in genes encoding sarcomeric or sarcomere-associated cardiac muscle proteins. The disease mainly affects adults, although young children with severe HCM have also been reported. We describe four unrelated neonates with lethal cardiomyopathy, and performed molecular studies to identify the genetic defect. We also present a literature overview of reported patients with compound heterozygous or homozygous pathogenic MYBPC3 mutations and describe their clinical characteristics. All four children presented with feeding difficulties, failure to thrive, and dyspnea. They died from cardiac failure before age 13 weeks. Features of left ventricular noncompaction were diagnosed in three patients. In the fourth, hypertrabeculation was not a clear feature, but could not be excluded. All of them had septal defects. Two patients were compound heterozygotes for the pathogenic c.2373dup p.(Trp792fs) and c.2827C>T p.(Arg943*) mutations, and two were homozygous for the c.2373dup and c.2827C>T mutations. All patients with biallelic truncating pathogenic mutations in MYBPC3 reported so far (n=21) were diagnosed with severe cardiomyopathy and/or died within the first few months of life. In 62% (13/21), septal defects or a patent ductus arteriosus accompanied cardiomyopathy. In contrast to heterozygous pathogenic mutations, homozygous or compound heterozygous truncating pathogenic MYBPC3 mutations cause severe neonatal cardiomyopathy with features of left ventricular noncompaction and septal defects in approximately 60% of patients.

A new common mutation in the cardiac beta-myosin heavy chain gene in Finnish patients with hypertrophic cardiomyopathy

BACKGROUND

In the nationwide FinHCM Study including 306 Finnish patients with hypertrophic cardiomyopathy (HCM), we have previously identified two founder mutations in the alpha-tropomyosin (TPM1-D175N) and myosin-binding protein C (MYBPC3-Q1061X) genes, accounting for 18% of all cases. Objective. To screen additional mutations, previously identified in eastern Finnish cohorts with HCM, in the FinHCM Study population.

PATIENTS AND METHODS

Ten mutations in the beta-myosin heavy chain gene (MYH7), TPM1, and MYBPC3 were screened.

RESULTS

MYH7-R1053Q was found in 17 of 306 patients (5.6%). No carriers of MYH7-R719W or N696S were found. A novel TPM1-D175G mutation was found in a single patient. MYBPC3 mutations were found in 14 patients: IVS5-2A-C in two, IVS14-13G-A in two, K811del in six, and A851insT in four patients. Altogether, a HCM-causing mutation was identified in 32 patients, accounting for 10.5% of all cases. In addition, two MYBPC3 variants R326Q and V896M with uncertain pathogenicity were found in eight and in 10 patients, respectively.

CONCLUSION

Combining the present findings with our previous results, a causative mutation was identified in 28% of the FinHCM cohort. MYH7-R1053Q was the third most common mutation, and should be screened in all new cases of HCM in Finland.

Detection of mutations in symptomatic patients with hypertrophic cardiomyopathy in Taiwan

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a common genetic cardiac disorder associated with sudden death, heart failure, and stroke. The aim of the present study was to evaluate the prevalence and types of mutations in symptomatic patients with HCM in Taiwan.

METHODS

Thirty-eight HCM index patients (mean age 60±16 years) underwent systematic mutation screening of eight sarcomeric genes: β-myosin heavy chain (MYH7), myosin-binding protein C (MYBPC3), troponin T (TNNT2), troponin I (TNNI3), myosin ventricular regulatory light chain 2 (MYL2), myosin ventricular essential light chain 1 (MYL3), α-tropomyosin (TPM1), and cardiac α-actin (ACTC), using direct DNA sequencing. In silico programs predicted damaging amino acids. In the positive families, genotype-phenotype correlation studies were done.

RESULTS

Overall, 13 mutations were identified in 13 index patients (34.2%). The three most frequently mutated genes were MYH7, MYBPC3, and TNNT2. One patient carried double mutations. Five mutations (MYH7 R147S; MYBPC3 R597Q; MYBPC3 W1007R; TNNI3 E124Q; MYL3 R63C) were novel; all were missense mutations. Analysis using in silico tools showed near consensus to classify these five novel mutations as pathological. Family pedigree analysis showed the presence of cosegregation in at least two affected members in each proband family, but incomplete penetrance in young family members with a positive genotype.

CONCLUSIONS

We identified 13 HCM pedigrees, including 5 carrying novel mutations and 1 with a double mutation. The three most commonly mutated genes were MYH7, MYBPC3, and TNNT2. These results, together with genetic counseling, could lead to earlier diagnosis and better management of family members at risk of HCM.

Yield of molecular and clinical testing for arrhythmia syndromes: report of 15 years' experience

BACKGROUND

Sudden cardiac death is often caused by inherited arrhythmia syndromes, particularly if it occurs at a young age. In 1996, we started a cardiogenetics clinic aimed at diagnosing such syndromes and providing timely (often presymptomatic) treatment to families in which such syndromes or sudden cardiac death existed. We studied the yield of DNA testing for these syndromes using a candidate-gene approach over our 15 years of experience.

METHODS AND RESULTS

We analyzed the yield of DNA testing. In subanalyses, we studied differences in the yield of DNA testing over time, between probands with isolated or familial cases and between probands with or without clear disease-specific clinical characteristics. In cases of sudden unexplained death (antemortem or postmortem analysis of the deceased not performed or providing no diagnosis), we analyzed the yield of cardiological investigations. Among 7021 individuals who were counseled, 6944 from 2298 different families (aged 41 ± 19 years; 49% male) were analyzed. In 702 families (31%), a possible disease-causing mutation was detected. Most mutations were found in families with long-QT syndrome (47%) or hypertrophic cardiomyopathy (46%). Cascade screening revealed 1539 mutation-positive subjects. The mutation detection rate decreased over time, in part because probands with a less severe phenotype were studied, and was significantly higher in familial than in isolated cases. We counseled 372 families after sudden unexplained death; in 29% of them (n=108), an inherited arrhythmia syndrome was diagnosed.

CONCLUSIONS

The proportion of disease-causing mutations found decreased over time, in part because probands with a less severe phenotype were studied. Systematic screening of families identified many (often presymptomatic) mutation-positive subjects.