A new missense mutation, Arg719Gln, in the beta-cardiac heavy chain myosin gene of patients with familial hypertrophic cardiomyopathy

Presence of Hypertrophic Cardiomyopathy Related Gene Mutations and Clinical Manifestations in Vietnamese Patients With Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is associated primarily with pathogenic mutations in sarcomeric genes. The aim of this study was to identify the prevalence and distribution of disease-causing mutations in HCM-associated genes and the genotype-phenotype relationship in Vietnamese patients with HCM.Methods and Results:Genetic testing was performed by next-generation sequencing in 104 unrelated probands for 23 HCM-related genes and in 57 family members for the mutation(s) detected. Clinical manifestations were recorded for genotype-phenotype correlation analysis. Mutation detection rate was 43.4%. Mutations inMYBPC3accounted for 38.6%, followed byTPM1(20.5%),MYH7(18.2%),TNNT2(9.1%),TNNI3(4.5%) andMYL2(2.3%). A mutation inGLAassociated with Fabry disease was found in 1 patient. A mutation inTPM1(c.842T>C, p.Met281Thr) was identified in 8 unrelated probands (18.2%) and 8 family members from 5 probands. Genotype-positive status related toMYH7,TPM1, andTNNT2mutations was associated with severe clinical manifestations.MYH7-positive patients displayed worse prognosis compared withMYBPC3-positive patients. Interestingly,TPM1c.842T>C mutation was associated with high penetrance and severe HCM phenotype.

CONCLUSIONS

We report for the first time the prevalence of HCM-related gene variants in Vietnamese patients with HCM.MYH7,TPM1, andTNNT2mutations were associated with unfavorable prognosis.

Prognostic predictive value of gene mutations in Japanese patients with hypertrophic cardiomyopathy

Although some studies have attempted to find useful prognostic factors in hypertrophic cardiomyopathy (HCM), those results are not fully helpful for use in actual clinical practice. Furthermore, several genetic abnormalities associated with HCM have been identified. However, the genotype-phenotype correlation in HCM remains to be elucidated. Here, we attempted to assess patients with different types of gene mutations causing HCM and investigate the prognosis. A total of 140 patients with HCM underwent a screening test for myofilament gene mutations by direct sequencing of eight sarcomeric genes. Patients with a single mutation in cardiac troponin T, cardiac troponin I, α-tropomyosin, and regulatory and essential light chains were excluded from the study because the number of cases was too small. The clinical presentations and outcomes of the remaining 127 patients with HCM, 31 β-myosin heavy chain (MYH7) mutation carriers, 19 cardiac myosin-binding protein C (MYBPC3) mutation carriers, and 77 mutation non-carriers were analyzed retrospectively. MYBPC3 mutation carriers had a high frequency of ventricular arrhythmia and syncope. Kaplan-Meier curves revealed no significant difference in prognosis among the three groups, but a lack of family history of sudden death (SD) and a past history of syncope were significantly related to poor prognosis. An absence of family history of SD and past history of syncope are useful prognostic factors in patients with HCM. MYH7 and MYBPC3 mutations did not significantly influence prognosis compared to non-carriers. However, patients with the MYBPC3 mutation should be closely followed for the possibility of SD.

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.

Genetic complexity in hypertrophic cardiomyopathy revealed by high-throughput sequencing

Background

Clinical interpretation of the large number of rare variants identified by high throughput sequencing (HTS) technologies is challenging. The aim of this study was to explore the clinical implications of a HTS strategy for patients with hypertrophic cardiomyopathy (HCM) using a targeted HTS methodology and workflow developed for patients with a range of inherited cardiovascular diseases. By comparing the sequencing results with published findings and with sequence data from a large-scale exome sequencing screen of UK individuals, we sought to quantify the strength of the evidence supporting causality for detected candidate variants.

Methods and results

223 unrelated patients with HCM (46±15 years at diagnosis, 74% males) were studied. In order to analyse coding, intronic and regulatory regions of 41 cardiovascular genes, we used solution-based sequence capture followed by massive parallel resequencing on Illumina GAIIx. Average read-depth in the 2.1 Mb target region was 120. Rare (frequency<0.5%) non-synonymous, loss-of-function and splice-site variants were defined as candidates. Excluding titin, we identified 152 distinct candidate variants in sarcomeric or associated genes (89 novel) in 143 patients (64%). Four sarcomeric genes (MYH7, MYBPC3, TNNI3, TNNT2) showed an excess of rare single non-synonymous single-nucleotide polymorphisms (nsSNPs) in cases compared to controls. The estimated probability that a nsSNP in these genes is pathogenic varied between 57% and near certainty depending on the location. We detected an additional 94 candidate variants (73 novel) in desmosomal, and ion-channel genes in 96 patients (43%).

Conclusions

This study provides the first large-scale quantitative analysis of the prevalence of sarcomere protein gene variants in patients with HCM using HTS technology. Inclusion of other genes implicated in inherited cardiac disease identifies a large number of non-synonymous rare variants of unknown clinical significance.

Early results of sarcomeric gene screening from the Egyptian National BA-HCM Program

The present study comprised sarcomeric genotyping of the three most commonly involved sarcomeric genes: MYBPC3, MYH7, and TNNT2 in 192 unrelated Egyptian hypertrophic cardiomyopathy (HCM) index patients. Mutations were detected in 40 % of cases. Presence of positive family history was significantly (p = 0.002) associated with a higher genetic positive yield (49/78, 62.8 %). The majority of the detected mutations in the three sarcomeric genes were novel (40/62, 65 %) and mostly private (47/62, 77 %). Single nucleotide substitution was the most frequently detected mutation type (51/62, 82 %). Over three quarters of these substitutions (21/27, 78 %) involved CpG dinucleotide sites and resulted from C > T or G > A transition in the three analyzed genes, highlighting the significance of CpG high mutability within the sarcomeric genes examined. This study could aid in global comparative studies in different ethnic populations and constitutes an important step in the evolution of the integrated clinical, translational, and basic science HCM program.

Founder mutations in hypertrophic cardiomyopathy patients in the Netherlands

In this part of a series on cardiogenetic founder mutations in the Netherlands, we review the Dutch founder mutations in hypertrophic cardiomyopathy (HCM) patients. HCM is a common autosomal dominant genetic disease affecting at least one in 500 persons in the general population. Worldwide, most mutations in HCM patients are identified in genes encoding sarcomeric proteins, mainly in the myosin-binding protein C gene (MYBPC3, OMIM #600958) and the beta myosin heavy chain gene (MYH7, OMIM #160760). In the Netherlands, the great majority of mutations occur in the MYBPC3, involving mainly three Dutch founder mutations in the MYBPC3 gene, the c.2373_2374insG, the c.2864_2865delCT and the c.2827C>T mutation. In this review, we describe the genetics of HCM, the genotype-phenotype relation of Dutch founder MYBPC3 gene mutations, the prevalence and the geographic distribution of the Dutch founder mutations, and the consequences for genetic counselling and testing. (Neth Heart J 2010;18:248-54.).

Mutation type is not clinically useful in predicting prognosis in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM), or clinically unexplained hypertrophy of the heart, is a common genetic cardiovascular disorder marked by genetic and phenotypic heterogeneity. As the genetic mutations underlying the pathogenesis of this disease have been identified, investigators have attempted to link mutations to clearly defined alterations in survival in hopes of identifying prognostically relevant biomarkers of disease. While initial studies labeling particular MYH7 -encoded beta myosin heavy chain and TNNT2 -encoded cardiac troponin T mutations as “malignant” or “benign” raised hopes for mutation-specific risk stratification in HCM, a series of subsequent investigations identified mutations in families with contradictory disease phenotypes. Furthermore, subsequent proband-based cohort studies indicated that the clinical prognostic relevance of individual mutations labeled as “malignant” or “benign” in large referral centers is negligible. Herein, we seek to summarize the controversy and dispute the notion that mutation-specific risk stratification in HCM is possible at the present time. We provide evidence for clinicians and basic scientists alike to move beyond simple mutation descriptors to a more nuanced understanding of HCM mutations that fully captures the multi-factorial nature of HCM disease expression.

Development of a high resolution melting method for the detection of genetic variations in hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiac disease affecting 1 in 500 people. Due to large cohorts to investigate, the number of disease-causing genes, the size of the 2 prevalent mutated genes, and the presence of a large spectrum of private mutations, mutational screening must be performed using an extremely sensitive and specific scanning method.

METHODS

High Resolution Melting (HRM) analysis was developed for prevalent HCM-causing genes (MYBPC3, MYH7, TNNT2, and TNNI3) using control DNAs and DNAs carrying previously identified gene variants. A cohort of 34 HCM patients was further blindly screened. To evaluate HRM sensitivity, this cohort was also screened using an optimized DHPLC methodology.

RESULTS

All gene variants detected by DHPLC were also readily identified as abnormal by HRM analysis. Mutational screening of a cohort of 34 HCM cases led to identification of 19 mutated alleles. Complete molecular investigation was completed two times faster and cheaper than using DHPLC strategy.

CONCLUSIONS

HRM analysis represents an inexpensive, highly sensitive and high-throughput method to allow identification of mutations in the coding sequences of prevalent HCM genes. Identification of more HCM mutations will provide new insights into genotype/phenotype relationships and will allow a better knowledge of the HCM physiopathology.

Serial observations and mutational analysis of an adoptee with family history of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited cardiac disease with an autosomal dominant mode of transmission. Comprehensive genetic screening of several genes frequently found mutated in HCM is recommended for first-degree relatives of HCM patients. Genetic testing provides the means to identify those at risk of developing HCM and to institute measures to prevent sudden cardiac death (SCD). Here, we present an adoptee whose natural mother and maternal relatives were known be afflicted with HCM and SCD. The proband was followed closely from age 6 to 17 years, revealing a natural history of the progression of clinical findings associated with HCM. Genetic testing of the proband and her natural mother, who is affected by HCM, revealed that they were heterozygous for both the R719Q and T1513S variants in the cardiac beta-myosin heavy chain (MYH7) gene. The proband's ominous family history indicates that the combination of the R719Q and T1513S variants in cis may be a "malignant" variant that imparts a poor prognosis in terms of the disease progression and SCD risk.

Risk stratification for sudden cardiac death in hypertrophic cardiomyopathy: systematic review of clinical risk markers

We performed a systematic literature review of recommended 'major' and 'possible' clinical risk markers for sudden cardiac death (SCD) in hypertrophic cardiomyopathy (HCM). We searched the Medline, Embase and Cochrane databases for articles published between 1971 and 2007. We included English language reports on HCM patients containing follow-up data on the endpoint (sudden) cardiac death using survival analysis. Analysis was undertaken using the quality of reporting of meta-analyses (QUORUM) statement checklist. The quality was checked using a quality assessment form from the Cochrane Collaboration. Thirty studies met inclusion criteria and passed quality assessment. The use of the six major risk factors (previous cardiac arrest or sustained ventricular tachycardia, non-sustained ventricular tachycardia, extreme left ventricular hypertrophy, unexplained syncope, abnormal blood pressure response, and family history of sudden death) in risk stratification for SCD as recommended by international guidelines was supported by the literature. In addition, left ventricular outflow tract obstruction seems associated with a higher risk of SCD. Our systematic review provides sound evidence for the use of the six major risk factors for SCD in the risk stratification of HCM patients. Left ventricular outflow tract obstruction could be included in the overall risk profile of patients with a marked left ventricular outflow gradient under basal conditions.

Shared genetic causes of cardiac hypertrophy in children and adults

BACKGROUND

The childhood onset of idiopathic cardiac hypertrophy that occurs without a family history of cardiomyopathy can portend a poor prognosis. Despite morphologic similarities to genetic cardiomyopathies of adulthood, the contribution of genetics to childhood-onset hypertrophy is unknown.

METHODS

We assessed the family and medical histories of 84 children (63 boys and 21 girls) with idiopathic cardiac hypertrophy diagnosed before 15 years of age (mean [+/-SD] age, 6.99+/-6.12 years). We sequenced eight genes: MYH7, MYBPC3, TNNT2, TNNI3, TPM1, MYL3, MYL2, and ACTC. These genes encode sarcomere proteins that, when mutated, cause adult-onset cardiomyopathies. We also sequenced PRKAG2 and LAMP2, which encode metabolic proteins; mutations in these genes can cause early-onset ventricular hypertrophy.

RESULTS

We identified mutations in 25 of 51 affected children without family histories of cardiomyopathy and in 21 of 33 affected children with familial cardiomyopathy. Among 11 of the 25 children with presumed sporadic disease, 4 carried new mutations and 7 inherited the mutations. Mutations occurred predominantly (in >75% of the children) in MYH7 and MYBPC3; significantly more MYBPC3 missense mutations were detected than occur in adult-onset cardiomyopathy (P<0.005). Neither hypertrophic severity nor contractile function correlated with familial or genetic status. Cardiac transplantation and sudden death were more prevalent among mutation-positive than among mutation-negative children; implantable cardioverter-defibrillators were more frequent (P=0.007) in children with family histories that were positive for the mutation.

CONCLUSIONS

Genetic causes account for about half of presumed sporadic cases and nearly two thirds of familial cases of childhood-onset hypertrophy. Childhood-onset hypertrophy should prompt genetic analyses and family evaluations.

Cardiovascular magnetic resonance signs of ischemia in hypertrophic cardiomyopathy

BACKGROUND

Recurrent myocardial ischemia has been recognized as playing an important role in the pathophysiology of hypertrophic cardiomyopathy (HCM) and cardiovascular magnetic resonance (CMR), with or without gadolinium, is a promising method of evaluating fibrosis, edema and hypoperfusion. The aim of this study is to evaluate the interrelationship between late enhancement (LE) and other signs of ischemia, such as edema and perfusion defects, and to relate them to clinical data in order to describe the stage of the disease.

METHODS

Forty-four patients were evaluated by CMR cine images, T2-weighted sequences for edema and LE sequences. First-pass perfusion study was obtained in 37 patients. Acute-subacute ischemic events were clinically defined as the presence of chest pain or new onset of ST-segment depression, end-stage phase by left ventricular ejection fraction <50% and maximal left ventricular wall thickness <25 mm.

RESULTS

Intramural patchy LE was found in 35/44 (80%) patients; extensive LE in 4/44 (9%). Edema was present in 24/44 (54%) patients and perfusion defects in 17/37 (46%). Simultaneous presence of patchy LE, edema and hypoperfusion in corresponding segments, was significantly associated to acute-subacute ischemic-phase parameters (p=0.02; RR 1.99, 95% C.I. 0.77-5.02). Extensive LE and perfusion defects in the absence of edema were significantly related to end-stage HCM (p<0.001; RR 13.7, 95% C.I. 1.83-102.05).

CONCLUSIONS

Using CMR in patients with HCM, we found focal tissue abnormalities consistent with regional ischemia at various stages. CMR provides important, clinically relevant information on the acuity, extent and functional relevance of ischemic injuries in HCM.

Gene-specific modifying effects of pro-LVH polymorphisms involving the renin-angiotensin-aldosterone system among 389 unrelated patients with hypertrophic cardiomyopathy

AIMS

The purpose of this study was to determine whether the deletion/insertion (D/I) polymorphism in the ACE-encoded angiotensin-converting enzyme or the pooled gene effect of five renin-angiotensin-aldosterone system (RAAS) polymorphisms were disease modifiers in a large cohort of unrelated patients with genotyped hypertrophic cardiomyopathy (HCM).

METHODS AND RESULTS

Five different RAAS polymorphism genotypes were established by PCR amplification of the surrounding polymorphic regions of genomic DNA in a cohort of 389 unrelated patients comprehensively genotyped for HCM-causing mutations in eight sarcomeric/myofilament genes. Patient clinical data were archived in a database blinded both to the primary myofilament defect and the polymorphism genotype. Each patient was assessed with respect to ACE genotype as well as composite pro-left ventricular hypertrophy (LVH) RAAS polymorphism score (0-5). Overall, no clinical parameter correlated independently with ACE genotype. Subset analysis of the two most common genetic subtypes of HCM, MYBPC3 (myosin binding protein C) and MYH7 (beta myosin heavy chain), demonstrated a significant pro-LVH effect of DD-ACE only in patients with MYBPC3-HCM. In MYBPC3-HCM, left ventricular wall thickness was greater in patients with DD genotype (25.8+/-5 mm) compared with DI (21.8+/-4) or II genotype (20.8+/-5, P=0.01). Moreover, extreme hypertrophy (>30 mm) was only seen in MYBPC3-HCM patients who also hosted DD-ACE. An effect of RAAS pro-LVH score was evident only in the subgroup of patients with no previously identified myofilament mutation.

CONCLUSION

This study demonstrates that RAAS genotypes may modify the clinical phenotype of HCM in a disease gene-specific fashion rather than indiscriminately.

Comprehensive Analysis of the Beta-Myosin Heavy Chain Gene in 389 Unrelated Patients With Hypertrophic Cardiomyopathy

OBJECTIVES

We sought to determine the prevalence and phenotype of beta-myosin heavy chain gene MYH7 mutations in a large cohort of unrelated patients with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Hypertrophic cardiomyopathy is a heterogeneous cardiac disease. MYH7 mutations are one of the most common genetic causes of HCM and have been associated with severe hypertrophy, young age of diagnosis, and high risk of sudden cardiac death. However, these clinical findings from large, family studies have not been confirmed in a large unrelated cohort.

METHODS

Deoxyribonucleic (DNA) samples obtained from 389 HCM outpatients seen at this tertiary referral center were analyzed for mutations, using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing for all 38 protein-coding exons of MYH7. Clinical data were extracted from patient records blinded to patient genotype.

RESULTS

Fifty-eight patients (15%) harbored 40 different mutations in MYH7. Compared with HCM patients without MYH7 mutations, HCM patients with MYH7 were younger at diagnosis (32.9 vs. 42.7 years, p = 0.0002), had more hypertrophy (left ventricular wall thickness of 24.2 vs. 21.1 mm, p = 0.0009), and more frequently underwent myectomy (60% vs. 38%, p = 0.002). The HCM patients with MYH7 mutations more often had a family history of HCM (43% vs. 29%, p = 0.006), but there was no difference in family history of sudden death (16% vs. 14%, p = NS).

CONCLUSIONS

In this setting, HCM patients with MYH7 were diagnosed at a younger age and had more hypertrophy, but they had no greater frequency of sudden death among first-degree relatives. Although these associations may prove useful for targeted gene screening, caution should be exercised in terms of using pathogenic status in risk stratification.

From malignant mutations to malignant domains: the continuing search for prognostic significance in the mutant genes causing hypertrophic cardiomyopathy

The genetic causes of hypertrophic cardiomyopathy are diverse and thus present challenges in the development of genetic tests to identify patients at risk

Hypertrophic cardiomyopathy: distribution of disease genes, spectrum of mutations, and implications for a molecular diagnosis strategy

BACKGROUND

Hypertrophic cardiomyopathy is an autosomal-dominant disorder in which 10 genes and numerous mutations have been reported. The aim of the present study was to perform a systematic screening of these genes in a large population, to evaluate the distribution of the disease genes, and to determine the best molecular strategy in clinical practice.

METHODS AND RESULTS

The entire coding sequences of 9 genes (MYH7, MYBPC3, TNNI3, TNNT2, MYL2, MYL3, TPM1, ACTC, andTNNC1) were analyzed in 197 unrelated index cases with familial or sporadic hypertrophic cardiomyopathy. Disease-causing mutations were identified in 124 index patients ( approximately 63%), and 97 different mutations, including 60 novel ones, were identified. The cardiac myosin-binding protein C (MYBPC3) and beta-myosin heavy chain (MYH7) genes accounted for 82% of families with identified mutations (42% and 40%, respectively). Distribution of the genes varied according to the prognosis (P=0.036). Moreover, a mutation was found in 15 of 25 index cases with "sporadic" hypertrophic cardiomyopathy (60%). Finally, 6 families had patients with more than one mutation, and phenotype analyses suggested a gene dose effect in these compound-heterozygous, double-heterozygous, or homozygous patients.

CONCLUSIONS

These results might have implications for genetic diagnosis strategy and, subsequently, for genetic counseling. First, on the basis of this experience, the screening of already known mutations is not helpful. The analysis should start by testing MYBPC3 and MYH7 and then focus on TNNI3, TNNT2, and MYL2. Second, in particularly severe phenotypes, several mutations should be searched. Finally, sporadic cases can be successfully screened.

Prevalence and severity of "benign" mutations in the beta-myosin heavy chain, cardiac troponin T, and alpha-tropomyosin genes in hypertrophic cardiomyopathy

BACKGROUND

Genotype-phenotype correlative studies have implicated 8 particular mutations that cause hypertrophic cardiomyopathy (HCM) as "benign defects," associated with near-normal survival: N232S, G256E, F513C, V606M, R719Q, and L908V of beta-myosin heavy chain (MYH7); S179F of troponin T (TNNT2); and D175N of alpha-tropomyosin (TPM1). Routine genetic screening of HCM patients for specific mutations is anticipated to provide important diagnostic and prognostic information. The frequency and associated phenotype of these mutations in a large, unselected cohort of HCM is unknown.

METHODS AND RESULTS

A total of 293 unrelated HCM patients were genotyped for the presence of a benign mutation. DNA was obtained after informed consent; specific MHY7, TNNT2, and TPM1 fragments were amplified by polymerase chain reaction; and the mutations were detected by denaturing high-performance liquid chromatography and automated DNA sequencing. Only 5 (1.7%) of the 293 patients possessed a benign mutation. Moreover, all 5 subjects with an ascribed benign mutation had already manifested clinically severe expression of HCM, with all 5 requiring surgical myectomy, 3 of the 5 having a family history of sudden cardiac death, and 1 adolescent requiring an orthotopic heart transplant.

CONCLUSIONS

These findings demonstrate the rarity of specific mutations in HCM and challenge the notion of mutation-specific clinical outcomes. Fewer than 2% of the subjects harbored a benign mutation, and those patients with a benign mutation experienced a very serious clinical course.

Prevalence and age-dependence of malignant mutations in the beta-myosin heavy chain and troponin T genes in hypertrophic cardiomyopathy: a comprehensive outpatient perspective

OBJECTIVES

The goal of this study was to determine the prevalence of "malignant" mutations in hypertrophic cardiomyopathy (HCM).

BACKGROUND

Previous genotype-phenotype studies have implicated four mutations (R403Q, R453C, G716R and R719W) as highly malignant defects in the beta-myosin heavy chain (MYH7). In the cardiac troponin T gene (TNNT2), a specific mutation (R92W) has been associated with high risk of sudden death. Routine clinical screening for these malignant mutations has been suggested to identify high-risk individuals.

METHODS

We screened 293 unrelated individuals with HCM seen at the Mayo Clinic in Rochester, Minnesota, between April 1997 and October 2000. Deoxyribonucleic acid (DNA) was obtained after informed consent; amplification of MYH7 exons 13 (R403Q), 14 (R453C) and 19 (G716R and R719W), and TNNT2 exon 9 (R92W) was performed by polymerase chain reaction. The mutations were detected using denaturing high-performance liquid chromatography and automated DNA sequencing.

RESULTS

The mean age at diagnosis was 42 years with 53 patients diagnosed before age 25. The mean maximal left ventricular wall thickness was 21 mm. Nearly one-third of cases were familial and one-fourth had a family history of sudden cardiac death. Only 3 of the 293 patients possessed one of the five "malignant" mutations, and all 3 patients were <25 years of age at presentation (p < 0.006).

CONCLUSIONS

This finding underscores the profound genetic heterogeneity in HCM. Only 1% of unrelated individuals seen at a tertiary referral center for HCM possessed one of the five "malignant" mutations that were examined. Routine clinical testing for these specific mutations is of low yield.

A malignant phenotype of hypertrophic cardiomyopathy caused by Arg719Gln cardiac beta-myosin heavy-chain mutation in a Chinese family

Mutations of the cardiac beta-myosin heavy-chain (beta-MHC) gene cause hypertrophic cardiomyopathy (HCM). Recent genotype-phenotype correlation studies have shown that mutations carry prognostic significance. We studied five unrelated Chinese families with hypertrophic cardiomyopathy. Exons 3-27 and 40 of the beta-MHC gene were screened with both the polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) method and the cycle sequencing of the PCR products. A previously reported heterozygous mutation Arg719Gln (arginine-->glutamine in codon 719) in exon 19 was found in one family. The proband is a 30-year-old female diagnosed at age of 25 years when she presented with symptoms of chest pain, palpitations, and frequent incidents of dizziness and syncope. A two-dimensional echocardiogram showed moderate asymmetrical septal hypertrophy with left atrial enlargement. There was no obstruction of the left ventricular outflow tract (LVOT). The patient also developed atrial fibrillation. The proband's mother and one of her sisters had similar clinical manifestations and both died suddenly at the age of 38 years. In addition, two silent nucleotide substitutions (ACT63ACC, TTT244TTC) in the cardiac beta-MHC gene were identified in the other four families. These synonymous mutations did not cosegregate with the disease in the families and they were also present in the 60 healthy and age-matched control subjects. Of the five families studied, we did not find any missense mutation in the remaining four families. The missense mutation Arg719Gln found in the Chinese family is associated with a malignant phenotype of severe clinical symptoms and poor survival prognosis. This mutation also causes atrial enlargement and atrial fibrillation. Our study provides further evidence that the mutation, which alters the charge of the myosin heavy chain, is associated with a serious clinical outcome.

Genotype-phenotype analysis in four families with mutations in beta-myosin heavy chain gene responsible for familial hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy is a genetically heterogeneous disease in which one of the most frequently implicated gene is the gene encoding the beta-myosin heavy chain. To date, more than 40 distinct mutations have been found within this gene. In order to progress on the determination of genotype-phenotype relationship, we have screened the beta-myosin heavy chain gene for mutations in 18 probands from unrelated families. We identified the mutation implicated in the disease in four families. Two of them, the Glu930 codon deletion and the Ile263Thr mutation, are reported here for the first time. The two other mutations are the Arg723Cys mutation, that was previously described in a proband as a de novo mutation, and the Arg719Trp mutation. A poor prognosis was associated with the Glu930codon deletion (mean maximal wall thickness (MWT) = 19.5 mm +/- 5) and the Arg719Trp mutation (mean MWT = 15.3 mm +/- 7), whereas a good prognosis was associated with the Arg723Cys mutation (mean MWT = 20.1 mm +/- 7). The combination of clinical and genetic characteristics of each family member suggests that prognosis is related neither to the degree of left ventricular wall thickness nor to a change in the net electrical charge of the protein. Additional family studies are needed to confirm these findings and to contribute to stratify the prognosis according to the mutation involved.

The origins of hypertrophic cardiomyopathy-causing mutations in two South African subpopulations: a unique profile of both independent and founder events

Hypertrophic cardiomyopathy (HCM) is an autosomal dominantly inherited disease of the cardiac sarcomere, caused by numerous mutations in genes encoding protein components of this structure. Mutation carriers are at risk of sudden cardiac death, mostly as adolescents or young adults. The reproductive disadvantage incurred may explain both the global occurrence of diverse independent HCM-associated mutations and the rare reports of founder effects within populations. We have investigated whether this holds true for two South African subpopulations, one of mixed ancestry and one of northern-European descent. Previously, we had detected three novel mutations-Ala797Thr in the beta-myosin heavy-chain gene (betaMHC), Arg92Trp in the cardiac troponin T gene (cTnT), and Arg645His in the myosin-binding protein C gene (MyBPC)-and two documented betaMHC mutations (Arg403Trp and Arg249Gln). Here we report three additional novel mutations-Gln499Lys in betaMHC and Val896Met and Deltac756 in MyBPC-and the documented betaMHC Arg719Gln mutation. Seven of the nine HCM-causing mutations arose independently; no conclusions can be drawn for the remaining two. However, the betaMHC Arg403Trp and Ala797Thr and cTnT Arg92Trp mutations were detected in another one, eight, and four probands, respectively, and haplotype analysis in families carrying these recurring mutations inferred their origin from three common ancestors. The milder phenotype of the betaMHC mutations may account for the presence of these founder effects, whereas population dynamics alone may have overridden the reproductive disadvantage incurred by the more lethal, cTnT Arg92Trp mutation.

Familial hypertrophic cardiomyopathy: from mutations to functional defects

Hypertrophic cardiomyopathy is characterized by left and/or right ventricular hypertrophy, which is usually asymmetric and involves the interventricular septum. Typical morphological changes include myocyte hypertrophy and disarray surrounding the areas of increased loose connective tissue. Arrhythmias and premature sudden deaths are common. Hypertrophic cardiomyopathy is familial in the majority of cases and is transmitted as an autosomal-dominant trait. The results of molecular genetics studies have shown that familial hypertrophic cardiomyopathy is a disease of the sarcomere involving mutations in 7 different genes encoding proteins of the myofibrillar apparatus: ss-myosin heavy chain, ventricular myosin essential light chain, ventricular myosin regulatory light chain, cardiac troponin T, cardiac troponin I, alpha-tropomyosin, and cardiac myosin binding protein C. In addition to this locus heterogeneity, there is a wide allelic heterogeneity, since numerous mutations have been found in all these genes. The recent development of animal models and of in vitro analyses have allowed a better understanding of the pathophysiological mechanisms associated with familial hypertrophic cardiomyopathy. One can thus tentatively draw the following cascade of events: The mutation leads to a poison polypeptide that would be incorporated into the sarcomere. This would alter the sarcomeric function that would result (1) in an altered cardiac function and then (2) in the alteration of the sarcomeric and myocyte structure. Some mutations induce functional impairment and support the pathogenesis hypothesis of a "hypocontractile" state followed by compensatory hypertrophy. Other mutations induce cardiac hyperfunction and determine a "hypercontractile" state that would directly induce cardiac hypertrophy. The development of other animal models and of other mechanistic studies linking the genetic mutation to functional defects are now key issues in understanding how alterations in the basic contractile unit of the cardiomyocyte alter the phenotype and the function of the heart.

Molecular genetic basis of hypertrophic cardiomyopathy: genetic markers for sudden cardiac death

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease caused by mutations in sarcomeric proteins. The disease is characterized by left ventricular hypertrophy in the absence of an increased external load, and myofibrillar disarray. A large number of mutations in genes coding for the beta-myosin heavy chain (beta-MyHC), cardiac troponin T (cTnT), cardiac troponin I, alpha-tropomyosin, myosin binding protein C (MyBP-C), and myosin light chain 1 and 2 in patients with HCM have been identified. Genotype-phenotype correlation studies have shown that mutations carry prognostic significance. The Gly256Glu, Val606Met, and Leu908Val mutations in the beta-MyHC are associated with a benign prognosis. In contrast, Arg403Gln, Arg719Trp, and Arg453Cys mutations are associated with a high incidence of sudden cardiac death (SCD). Mutations in cTnT are associated with a mild degree of hypertrophy, but a high incidence of SCD. Mutations in MyBP-C are associated with mild hypertrophy and a benign prognosis. However, it has become evident that factors other than the underlying mutations, such as genetic background and possibly environmental factors, also modulate phenotypic expression of HCM.

Characterization of mutant myosins of Dictyostelium discoideum equivalent to human familial hypertrophic cardiomyopathy mutants. Molecular force level of mutant myosins may have a prognostic implication

Recent studies have revealed that familial hypertrophic cardiomyopathy (FHC) is caused by missence mutations in myosin heavy chain or other sarcomeric proteins. To investigate the functional impact of FHC mutations in myosin heavy chain, mutants of Dictyostelium discoideum myosin II equivalent to human FHC mutations were generated by site-directed mutagenesis, and their motor function was characterized at the molecular level. These mutants, i.e., R397Q, F506C, G575R, A699R, K703Q, and K703W are respectively equivalent to R403Q, F513C, G584R, G716R, R719Q, and R719W FHC mutants. We measured the force generated by these myosin mutants as well as the sliding velocity and the actin-activated ATPase activity. These measurements showed that the A699R, K703Q, and K703W myosins exhibited unexpectedly weak affinity with actin and the lowest level of force, though their ATPase activity remained rather high. F506C mutant which has been reported to have benign prognosis exhibited the least impairment of the motile and enzymatic activities. The motor functions of R397Q and G575R myosins were classified as intermediate. These results suggest that the force level of mutant myosin molecule may be one of the key factors for pathogenesis which affect the prognosis of human FHC.

Molecular mechanisms regulating the myofilament response to Ca2+: implications of mutations causal for familial hypertrophic cardiomyopathy

In this chapter we consider a current perception of the molecular mechanisms controlling myofilament activation with emphasis on alterations that may occur in familial hypertrophic cardiomyopathy (FHC). FHC is a sarcomeric disease (100) with an autosomal dominant pattern of heritability (27, 51). There is a substantial body of evidence implicating missense mutations in the beta-MHC gene as causal for the development of this disease. Recently, mutations in genes of two thin filament regulatory proteins, cardiac troponin T(cTnT) and alpha-tropomyosin (alpha-Tm), have also been linked to FHC. The commonality among the functional consequences of these mutations remains an important question. This review discusses how these pathological mutations may impact the activation process by disrupting critical structure function relations in both the thick and thin filaments.

Codon 102 of the cardiac troponin T gene is a putative hot spot for mutations in familial hypertrophic cardiomyopathy

BACKGROUND

Familial hypertrophic cardiomyopathy is a phenotypically and genetically heterogeneous disease. In some families, the disease is linked to the CMH2 locus on chromosome 1q3, in which the cardiac troponin T gene (TNNT2) has been identified as the disease gene. The mutations found in this gene appear to be associated with incomplete penetrance and poor prognosis. Because mutational hot spots offer unique possibilities for analysis of genotype-phenotype correlations, new missense mutations that could define such hot spots in TNNT2 were looked for in unrelated French families with familial hypertrophic cardiomyopathy.

METHODS AND RESULTS

Family members were genotyped with microsatellite markers to detect linkage to the four known disease loci. In family 715, analyses showed linkage to CMH2 only. To accurately position potential mutations on TNNT2, its partial genomic organization was established. Screening for mutations was performed by single-strand conformation polymorphism analysis and sequencing. A new missense mutation, Arg102Leu, was identified in affected members of family 715 because of a G-->T transversion located in the 10th exon of the gene. Penetrance of this new mutation is complete; echocardiographic data show a wide range of hypertrophy; and there was no sudden cardiac death in this family.

CONCLUSIONS

The codon 102 of the TNNT2 gene is a putative mutational hot spot in familial hypertrophic cardiomyopathy and is associated with phenotypic variability. Analysis of more pedigrees carrying mutations in this codon is necessary to better characterize the clinical and prognostic implications of TNNT2 mutations.

DNA testing in familial hypertrophic cardiomyopathy: clinical and laboratory implications

Counselling and clinical assessment in familial hypertrophic cardiomyopathy (FHC) is difficult, particularly in the young, since echocardiographic and ECG changes may not be diagnostic and clinical severity can vary. From 1990, when the beta-cardiac myosin heavy chain gene was implicated in the aetiology of FHC, considerable information about the molecular genetics of this disorder has emerged. However, an important question facing health professionals is the practical significance of DNA testing in FHC. The present study describes a DNA-based approach to screening for five commonly reported mutations involving the beta-cardiac myosin heavy chain gene. Approximately 11% of randomly selected families had an abnormality detected.

Contractile protein mutations and heart disease

Mutations in several muscle structural proteins (the myosin heavy chain, alpha tropomyosin, cardiac troponin T and myosin binding protein C) result in a genetically dominant heart disease, hypertrophic cardiomyopathy. Biochemical data from studies of mutant myosin suggest a dominant-negative mechanism for inheritance of this disease. The most likely primary defect is sarcomere dysfunction, which is followed by the major clinical symptoms.

Structural interpretation of the mutations in the beta-cardiac myosin that have been implicated in familial hypertrophic cardiomyopathy

In 10-30% of hypertrophic cardiomyopathy kindreds, the disease is caused by > 29 missense mutations in the cardiac beta-myosin heavy chain (MYH7) gene. The amino acid sequence similarity between chicken skeletal muscle and human beta-cardiac myosin and the three-dimensional structure of the chicken skeletal muscle myosin head have provided the opportunity to examine the structural consequences of these naturally occurring mutations in human beta-cardiac myosin. This study demonstrates that the mutations are related to distinct structural and functional domains. Twenty-four are clustered around four specific locations in the myosin head that are (i) associated with the actin binding interface, (ii) around the nucleotide binding site, (iii) adjacent to the region that connects the two reactive cysteine residues, and (iv) in close proximity to the interface of the heavy chain with the essential light chain. The remaining five mutations are in the myosin rod. The locations of these mutations provide insight into the way they impair the functioning of this molecular motor and also into the mechanism of energy transduction.