Evidence of genetic heterogeneity in five kindreds with familial hypertrophic cardiomyopathy

Identification of variants in genes associated with hypertrophic cardiomyopathy in Mexican patients

The objective of this work was to identify genetic variants in Mexican patients diagnosed with hypertrophic cardiomyopathy (HCM). According to world literature, the genes mainly involved are MHY7 and MYBPC3, although variants have been found in more than 50 genes related to heart disease and sudden death, and to our knowledge there are no studies in the Mexican population. These variants are reported and classified in the ClinVar (PubMed) database and only some of them are recognized in the Online Mendelian Information in Men (OMIM). The present study included 37 patients, with 14 sporadic cases and 6 familial cases, with a total of 21 index cases. Next-generation sequencing was performed on a predesigned panel of 168 genes associated with heart disease and sudden death. The sequencing analysis revealed twelve (57%) pathogenic or probably pathogenic variants, 9 of them were familial cases, managing to identify pathogenic variants in relatives without symptoms of the disease. At the molecular level, nine of the 12 variants (75%) were single nucleotide changes, 2 (17%) deletions, and 1 (8%) splice site alteration. The genes involved were MYH7 (25%), MYBPC3 (25%) and ACADVL, KCNE1, TNNI3, TPM1, SLC22A5, TNNT2 (8%). In conclusion; we found five variants that were not previously reported in public databases. It is important to follow up on the reclassification of variants, especially those of uncertain significance in patients with symptoms of the condition. All patients included in the study and their relatives received family genetic counseling.

Insights into human beta-cardiac myosin function from single molecule and single cell studies

beta-Cardiac myosin is a mechanoenzyme that converts the energy from ATP hydrolysis into a mechanical force that drives contractility in muscle. Thirty percent of the point mutations that result in hypertrophic cardiomyopathy are localized to MYH7, the gene encoding human beta-cardiac myosin heavy chain (beta-MyHC). Force generation by myosins requires a tight and highly conserved allosteric coupling between its different protein domains. Hence, the effects of single point mutations on the force generation and kinetics of beta-cardiac myosin molecules cannot be predicted directly from their location within the protein structure. Great insight would be gained from understanding the link between the functional defect in the myosin protein and the clinical phenotypes of patients expressing them. Over the last decade, several single molecule techniques have been developed to understand in detail the chemomechanical cycle of different myosins. In this review, we highlight the single molecule techniques that can be used to assess the effect of point mutations on beta-cardiac myosin function. Recent bioengineering advances have enabled the micromanipulation of single cardiomyocyte cells to characterize their force-length dynamics. Here, we briefly review single cell micromanipulation as an approach to determine the effect of beta-MyHC mutations on cardiomyocyte function. Finally, we examine the technical challenges specific to studying beta-cardiac myosin function both using single molecule and single cell approaches.

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.

Genetic basis of cardiomyopathy

The molecular basis of cardiac growth and development is a fundamental question that has intrigued many investigators in cardiovascular research. Adult cardiomyocytes are terminally differentiated and lose their ability to proliferate shortly after birth; however, in response to injury, myocytes have the capacity to synthesize new DNA and exhibit plasticity by a compensatory growth response, as is shown by re-expression of the fetal isoforms of many muscle-specific genes, which is characteristic of the proliferative response. The long-term effects of these compensatory responses may lead to the development and progression of diseases such as hypertrophic cardiomyopathy and dilated cardiomyopathy, because of a single point mutation. This concept has engaged scientists to investigate human models to explore the molecular basis of hypertrophy or dilation of the myocardium.

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.

The in vitro motility activity of beta-cardiac myosin depends on the nature of the beta-myosin heavy chain gene mutation in hypertrophic cardiomyopathy

Several mutations in the beta-myosin heavy chain gene cause hypertrophic cardiomyopathy. This study investigates (1) the in vitro velocities of translocation of fluorescently-labelled actin by beta-myosin purified from soleus muscle of 30 hypertrophic cardiomyopathy patients with seven distinct beta-myosin heavy chain gene mutations: Thr124Ile, Tyr162Cys, Gly256Glu, Arg403Gln, Val606Met, Arg870His, and Leu908Val mutations; and (2) motility activity of beta-myosin purified from cardiac and soleus muscle biopsies in the same patients. The velocity of translocation of actin by beta-myosin purified from soleus or cardiac muscle of 22 normal controls was 0.48 +/- 0.09 micron s-1. By comparison, the motility activity was reduced in all 30 patients with beta-myosin heavy chain gene mutations (range, 0.112 +/- 0.041 to 0.292 +/- 0.066 micron s-1. Notably, the Tyr162Cys and Arg403Gln mutations demonstrated significantly lower actin sliding velocities: 0.123 +/- 0.044, and 0.112 +/- 0.041 micron s-1, respectively. beta-myosin purified from soleus muscle from four patients with the Arg403Gln mutation had a similar actomyosin motility activity compared to beta-myosin purified from their cardiac biopsies (0.127 +/- 0.045 micron s-1 versus 0.119 +/- 0.068 micron s-1, respectively). Since these seven mutations lie in several distinct functional domains, it is likely that the mechanisms of their inhibitions of motility are different.

Hypertrophic cardiomyopathy: evaluation and treatment of patients at high risk for sudden death

Hypertrophic cardiomyopathy (HCM) is a heritable disease characterized by LV hypertrophy with markedly variable clinical, morphological, and genetic manifestations. It is the most common cause of sudden death in otherwise healthy young individuals. HCM patients often have disabling symptoms and are prone to arrhythmias. Frequently, there is associated LV systolic and diastolic dysfunction, LV outflow obstruction, and myocardial ischemia. Over the past decade, progress has been made in identifying patients who are at high risk for sudden death, in elucidating potential mechanisms of sudden death, and in defining therapeutic algorithms that may improve prognosis. It has also been possible to determine the genetic defect in some of the patients and to correlate clinical findings with the molecular defects. An exciting development has been the use of dual chamber pacemaker as an alternative to cardiac surgery to improve symptoms and relieve LV outflow obstruction.

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.

Familial hypertrophic cardiomyopathy: diagnostic and therapeutic implications of recent genetic studies

Familial hypertrophic cardiomyopathy is the first primary cardiomyopathy to have yielded to the techniques of modern molecular genetics. In the past few years, four genes responsible for this disease have been identified, all of which code for sarcomeric structural proteins. In addition, structure-function analysis and genotype-phenotype correlation studies have shed significant light on the molecular basis of this disease. It is hoped that within the next few years the application of molecular genetic tools will not only facilitate the diagnosis of hypertrophic cardiomyopathy but will also provide prognostic and therapeutic stratification for more definitive therapy.

Malignant familial hypertrophic cardiomyopathy in a family with a 453Arg-->Cys mutation in the beta-myosin heavy chain gene: coexistence of sudden death and end-stage heart failure

Recent genotype-phenotype correlation studies in familial hypertrophic cardiomyopathy (FHC) have revealed that some mutations in the beta- myosin heavy chain (BMHC) gene may be associated with a high incidence of sudden death and a poor prognosis. Coexistence of sudden death and end-stage heart failure in several families with FHC has recently being reported; however, the genetic basis of such families has not been clearly demonstrated. A three-generation Chinese familial hypertrophic cardiomyopathy (FHC) family (family HLI) with two cases of end-stage heart failure and three cases of sudden death was analyzed. The average age of death in the affected members in this family was 34 years old. Genetic linkage analysis using polymorphisms in the (alpha- and beta-myosin heavy chain genes revealed that FHC in this family is significantly linked to the BMHC gene without recombinations. Single-strand conformation polymorphism analysis of exons 8, 9 and 13 to 23 in the BMHC gene showed a polymorphic band on exon 14 that is in complete linkage with the disease status in this family. DNA sequencing analysis in the affected members revealed an 453Arg-->Cys mutation in the BMHC gene. To our knowledge this is the first reported mutation of FHC in Chinese. Our data suggest that the 453Arg-->Cys mutation is associated with a malignant clinical course in FHC due not only to sudden death but also to end-stage heart failure.

Mapping the locus for familial hypertrophic cardiomyopathy to chromosome 11 in a family with a case of apical hypertrophic cardiomyopathy of the Japanese type

To identify the disease locus of familial hypertrophic cardiomyopathy (FHC) in a Chinese family, a genetic linkage study was performed using polymorphisms from various chromosomal regions. This family has eight affected members, including a case with typical features of apical hypertrophic cardiomyopathy of the Japanese type. The results revealed significant evidence of linkage of polymorphisms on chromosome 11p13-q13 and FHC in this family with a maximal lod score of 3.38 at theta = 0.00. Our data suggest that the locus responsible for FHC in this family maps to chromosome 11 and that the molecular basis of FHC in the case of apical hypertrophic cardiomyopathy of the Japanese type might be similar to that of other affected members in the same family. Further studies are needed to elucidate the whole spectrum of the genetic basis of apical hypertrophic cardiomyopathy of the Japanese type.

Clinical and prognostic evaluation of familial hypertrophic cardiomyopathy in two South African families with different cardiac beta myosin heavy chain gene mutations

BACKGROUND

Familial hypertrophic cardiomyopathy is the most common inherited cardiac disorder, with sudden cardiac death at a young age the most frequent cause of death in affected individuals. Some cases of familial hypertrophic cardiomyopathy are caused by missense mutations of the beta myosin heavy chain (beta MHC) gene on chromosome 14 and at least 17 such mutations have been described. Recent reports suggest that a correlation exists between a specific beta MHC gene mutation and prognosis in familial hypertrophic cardiomyopathy. This premise is currently being used as a basis to provide counselling for affected families. This mutation/prognosis association, however, has not been widely assessed as yet. The clinical and prognostic features of two South African families of mixed racial descent, in which different beta MHC gene mutations were segregating, were studied to evaluate this correlation. The results were compared with those of previously published reports of European families carrying the same mutations.

METHODS

The beta MHC gene missense mutations in two affected families were identified by single strand conformation polymorphism analysis and sequencing (pedigree 106: Arg403Trp; pedigree 108: Arg249Gln). All family members were subjected to genotypic analysis using polymerase chain reaction amplification and restriction enzyme based mutation detection techniques. Clinical, electrocardiographic, and echocardiographic studies were performed on genotypically affected individuals in these two kindreds.

RESULTS

The number of individuals identified in pedigree 106 with the Arg403Trp mutation was 32.10 individuals bore the Arg249Gln mutation in pedigree 108. The penetrance rate in adults (equal to or greater than 16 years), using the strict echocardiographic criterion of maximum left ventricular wall thickness > or = 13 mm, was 25% for pedigree 106 and 33% for pedigree 108. Familial hypertrophic cardiomyopathy compatible electrocardiographic and echocardiographic abnormalities were seen in 60% of genotypically positive individuals aged > or = 16 years in pedigree 106 and 80% in pedigree 108. The prognosis was uniformly benign in the two families. For pedigree 106 this corresponded to a report of no early sudden cardiac deaths in a French family with the Arg403Trp mutation. For pedigree 108 the absence of such deaths was in apparent contrast to the four cases reported in 24 genotypically affected individuals in a study of a kindred of European ancestry bearing the Arg249Gln mutation.

CONCLUSION

This study of a large South African kindred confirmed the benign nature of the Arg403Trp mutation suggested in a previous report. The number and the relatively young age of affected individuals in a second South African family must be considered when comparing the absence of familial hypertrophic cardiomyopathy associated deaths with the intermediate survival reported for the Arg249Gln mutation in a European family. This investigation lends support to current evidence relating specific beta MHC gene mutations to prognosis, which may be used as a basis to provide counselling for affected families.

Sudden cardiac death in patients with hypertrophic cardiomyopathy: from bench to bedside with an emphasis on genetic markers

Hypertrophic cardiomyopathy (HCM) is the most common cause of death in the young, particularly in young competitive athletes. Death often occurs suddenly in asymptomatic, apparently healthy individuals. Several clinical parameters as well as genetic factors have been characterized that can identify those HCM patients who are at high risk for sudden cardiac death (SCD). The clinical parameters that have some predictive values for SCD in HCM patients are the following: a prior history of SCD, a family history of SCD, history of syncope, symptomatic ventricular tachycardia on Holter monitoring, inducible ventricular tachycardia during electrophysiologic studies, and myocardial ischemia in children with HCM. Recent identification of mutations in the beta myosin heavy chain gene and genotype-phenotype correlation in HCM patients have shown that the beta myosin heavy chain mutations are also prognosticators in HCM families. Several mutations such as Arg403Gln and Arg719Gln are associated with a high incidence of SCD, while Leu908Val mutation is associated with a benign course and a low incidence of SCD in HCM families. Additional genetic factors such as a polymorphism in angiotensin-converting enzyme I gene may also contribute to a high incidence of SCD in HCM families. Identification and characterization of HCM patients at high risk for SCD provide the opportunity to render prophylactic therapeutic interventions, such as implantation of defibrillators, in these individuals.

Abnormal contractile properties of muscle fibers expressing beta-myosin heavy chain gene mutations in patients with hypertrophic cardiomyopathy

Missense mutations in the beta-myosin heavy chain (beta-MHC) gene cause hypertrophic cardiomyopathy (HCM). As normal and mutant beta-MHCs are expressed in slow-twitch skeletal muscle of HCM patients, we compared the contractile properties of single slow-twitch muscle fibers from patients with three distinct beta-MHC gene mutations and normal controls. Fibers with the 741Gly-->Arg mutation (near the binding site of essential light chain) demonstrated decreased maximum velocity of shortening (39% of normal) and decreased isometric force generation (42% of normal). Fibers with the 403Arg-->Gln mutation (at the actin interface of myosin) showed lowered force/stiffness ratio (56% of normal) and depressed velocity of shortening (50% of normal). Both the 741Gly-->Arg and 403Arg-->Gln mutation-containing fibers displayed abnormal force-velocity relationships and reduced power output. Fibers with the 256Gly-->Glu mutation (end of ATP-binding pocket) had contractile properties that were indistinguishable from normal. Thus there is variability in the nature and extent of functional impairments in skeletal fibers containing different beta-MHC gene mutations, which may correlate with the severity and penetrance of the disease that results from each mutation. These functional alterations likely constitute the primary stimulus for the cardiac hypertrophy that is characteristic of this disease.

The cardiac myosin heavy chain Arg-403-->Gln mutation that causes hypertrophic cardiomyopathy does not affect the actin- or ATP-binding capacities of two size-limited recombinant myosin heavy chain fragments

Our aim was to investigate the potential functional consequences of myosin heavy chain (MHC) mutations identified in patients with familial hypertrophic cardiomyopathy. We observed the presence of a mutated beta-MHC mRNA in a formalin-fixed paraffin-embedded myocardial tissue of a proband from family A, which Geisterfer-Lowrance et al. [Geisterfer-Lowrance, Kass, Tanigawa, Vosberg, McKenna, Seidman and Seidman (1990) Cell 62, 999-1006] identified as carrying the Arg-403 to Gln mutation. Recombinant DNA methods were then used to obtain size-limited, soluble and undenatured fragments of mutated myosin subfragment 1 focused around the 403 mutation. The present analysis indicated that the 403 mutation did not quantitatively alter the actin- or ATP-binding capacities of two 246-residue or 524-residue-long recombinant MHC fragments containing this mutation. The absence of any apparent impact of the 403 mutation in the recombinant MHC fragments on interactions between actin and ATP is discussed in relation to numerous biochemical and structural reports which demonstrate the crucial role of the central MHC segment, where the 403 mutation occurs, in myosin functions.

Molecular genetics of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is genetically and phenotypically a heterogeneous disease. Genes identified include the beta myosin heavy chain gene (beta MHC) on chromosome 14q1, the troponin T gene on chromosome 1q, and the alpha tropomyosin gene on chromosome 15q. In addition, a fourth locus is present on chromosome 11q11, but the gene remains to be identified. More than 35 missense mutations in the beta MHC, 3 mutations in troponin T, and 2 mutations in alpha tropomyosin gene in HCM patients have been identified. Functional studies have shown that the mutant beta MHC protein has impaired actomyosin interaction and that expression of the mutant myosin disrupts the assembly of sarcomere in feline cardiocytes. Genotype-phenotype correlations of beta MHC mutations have shown that mutations such as Arg403Gln, Arg453Cys, and Arg719Trp are associated with a high incidence of sudden cardiac death and a significantly decreased life expectancy, whereas mutations Gly256Glu and Leu908Val have a near-normal life span. Preclinical genetic diagnosis should help in genetic counseling and therapeutic stratification.

Hereditary dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a common and important cause of morbidity and mortality. Many factors can contribute to the development of this disorder, although most commonly the etiology is unexplained. However, recent studies in individuals with idiopathic DCM now reveal a heritable cause in 20-30% of individuals. Diverse modes of inheritance have been demonstrated, encompassing an autosomal dominant type (by far the most common), together with recessive and X-linked forms, and maternal inheritance through mitochondrial DNA. The hereditary forms of DCM (HDCM) predominantly affect the left ventricle, although inherited abnormalities affecting primarily the right ventricle also are described. HDCM may occur as a primary cardiomyopathy, or secondary to inherited systemic metabolic or neuromuscular disorders. The causative genes for primary HDCM of the autosomal dominant and recessive types have not yet been discovered, but the combination of family pedigree analysis and phenotyping by echocardiography, together with new genetic techniques, should now allow their identification. Knowledge of the gene or genes responsible for HDCM would improve diagnostic accuracy, facilitate genetic counseling, advance understanding of pathogenesis, and provide the starting point for new methods of treatment. Because of the frequently heritable nature of DCM, it is of great importance that a diligent search for all potentially affected family members be undertaken.

Familial hypertrophic cardiomyopathy. Microsatellite haplotyping and identification of a hot spot for mutations in the beta-myosin heavy chain gene

Familial hypertrophic cardiomyopathy (FHC) is a clinically and genetically heterogeneous disease. The first identified disease gene, located on chromosome 14q11-q12, encodes the beta-myosin heavy chain. We have performed linkage analysis of two French FHC pedigrees, 720 and 730, with two microsatellite markers located in the beta-myosin heavy chain gene (MYO I and MYO II) and with four highly informative markers, recently mapped to chromosome 14q11-q12. Significant linkage was found with MYO I and MYO II in pedigree 720, but results were not conclusive for pedigree 730. Haplotype analysis of the six markers allowed identification of affected individuals and of some unaffected subjects carrying the disease gene. Two novel missense mutations were identified in exon 13 by direct sequencing, 403Arg-->Leu and 403Arg-->Trp in families 720 and 730, respectively. The 403Arg-->Leu mutation was associated with incomplete penetrance, a high incidence of sudden deaths and severe cardiac events, whereas the consequences of the 403Arg-->Trp mutation appeared less severe. Haplotyping of polymorphic markers in close linkage to the beta-myosin heavy chain gene can, thus, provide rapid analysis of non informative pedigrees and rapid detection of carrier status. Our results also indicate that codon 403 of the beta-myosin heavy chain gene is a hot spot for mutations causing FHC.

Left ventricular hypertrophy and morphology in familial hypertrophic cardiomyopathy associated with mutations of the beta-myosin heavy chain gene

OBJECTIVES

The purpose of this study was to determine the spectrum of left ventricular hypertrophy and ventricular morphology in adults with hypertrophic cardiomyopathy due to mutations of the beta-myosin heavy-chain gene.

BACKGROUND

Although echocardiography is an important test in diagnosing hypertrophic cardiomyopathy, the lack of an independent diagnostic criterion has been an obstacle in determining the full echocardiographic spectrum of this disease. Mutations in the beta-myosin heavy chain gene occur in approximately 50% of familial cases; in members of families with a known mutation, the diagnosis can be made with certainty.

METHODS

Echocardiograms from 39 genetically affected and 30 genetically unaffected adult family members over age 16 years from 10 families were analyzed. Left ventricular wall thickness was measured at 10 separate locations, and the presence of systolic anterior motion of the mitral valve, right ventricular hypertrophy and left ventricular morphology was evaluated independently by three separate observers without knowledge of the genetic diagnosis.

RESULTS

The mean maximal wall thickness in the genetically affected group was 24 +/- 8 mm (range 11 to 40), compared with 11 +/- 2 mm (range 7 to 16) in the unaffected group (p < 0.0001). Systolic anterior motion of the mitral valve or chordae tendineae with or without leaflet-septal contact was present in 62% of the affected group and in none of the unaffected group. The morphologic finding of reversed septal curvature was present in 79% of the affected group and in none of the unaffected group. Seventy-seven percent of patients in the affected group had a septal/free wall ratio > or = 1.3 compared with 6% in the unaffected group, with a septal/posterior wall ratio > or = 1.3 associated with only a 55% probability of being affected.

CONCLUSIONS

The two-dimensional echocardiographic spectrum of hypertrophic cardiomyopathy in a genetically defined adult population is broad. Previous echocardiographic criteria may be too strict to diagnose the disease in some patients who are genetically affected and therefore at risk for adverse events related to the disease. Ultimately, genetic testing may supersede echocardiography in diagnosing hypertrophic cardiomyopathy.

Mapping of a novel gene for familial hypertrophic cardiomyopathy to chromosome 11

Familial hypertrophic cardiomyopathy (FHC) is a cardiac disorder transmitted as an autosomal dominant trait. FHC has been shown to be genetically heterogeneous with less than 50% of published pedigrees being associated with mutations in the beta myosin heavy chain (beta-MHC) gene on chromosome 14q11-q12. A second locus has recently been reported on chromosome 1. We examined the segregation of microsatellite markers in a French pedigree for which the disease is not linked to beta-MHC gene. We found significant linkage of the disease locus to several (CA)n repeats located on chromosome 11 (lod scores between +3.3 and +4.98). The data suggest the localization of the novel FHC gene in a region spanning 17 centiMorgans.

Skeletal muscle expression and abnormal function of beta-myosin in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is an important inherited disease. The phenotype has been linked, in some kindreds, to the beta-myosin heavy chain (beta-MHC) gene. Missense and silent mutations in the beta-MHC gene were used as markers to demonstrate the expression of mutant and normal cardiac beta-MHC gene message in skeletal muscle of hypertrophic cardiomyopathy patients. Mutant beta-myosin, also shown to be present in skeletal muscle by Western blot analysis, translocated actin filaments slower than normal controls in an in vitro motility assay. Thus, single amino acid changes in beta-myosin result in abnormal actomyosin interactions, confirming the primary role of missense mutations in beta-MHC gene in the etiology of hypertrophic cardiomyopathy.

Missense mutations in the beta-myosin heavy-chain gene cause central core disease in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an important cause of sudden death in apparently healthy young individuals. In less than half of kindreds with HCM, the disease is linked to the beta-myosin heavy-chain gene locus (MYH7). We have recently described two missense MYH7 gene mutations [Arg-403 to Gln (R403Q) and Leu-908 to Val (L908V)] and found that the mutant message is present in skeletal muscle soleus) and that the mutant beta-myosin obtained from soleus muscle has abnormal in vitro motility activity. Having identified a second kindred with the R403Q mutation, and 3 other kindreds with two additional mutations (G741R and G256E), we performed histochemical analysis of soleus muscle biopsies from 25 HCM patients with one of these four mutations. Light microscopic examination of the NADH-stained biopsies revealed the presence of central core disease (CCD) of skeletal muscle, a rare autosomal dominant nonprogressive myopathy characterized by a predominance of type I "slow" fibers and an absence of mitochondria in the center of many type I fibers. CCD was present in 10 of 13 patients with the L908V mutation, 5 of 8 patients with the R403Q mutation, 1 of 3 patients with the G741R mutation, and 1 patient with the G256E mutation. Mild-to-moderate myopathic changes with muscle fiber hypertrophy were present in 16 patients. Notably, CCD was present in 2 adults and 3 children with the L908V mutation who did not have cardiac hypertrophy. In contrast, soleus muscle samples from 5 patients from 4 kindreds in which HCM was not linked to the MYH7 locus showed no myopathy or CCD. Soleus muscle biopsies from 5 control subjects also showed normal histology. This work demonstrates that (i) MYH7-associated HCM is often a disease of striated muscle but with predominant cardiac involvement and (ii) a subset of HCM patients with MYH7 gene missense mutations have CCD.

Sporadic hypertrophic cardiomyopathy due to de novo myosin mutations

Hypertrophic cardiomyopathy occurs as an autosomal dominant familial disorder or as a sporadic disease without familial involvement. While missense mutations in the beta cardiac myosin heavy chain (MHC) gene account for approximately half of all cases of familial hypertrophic cardiomyopathy, the molecular causes of sporadic hypertrophic cardiomyopathy are unknown. To determine whether beta cardiac MHC mutations are also associated with sporadic disease, we screened this gene in seven individuals with sporadic hypertrophic cardiomyopathy. Mutations in the beta cardiac MHC genes were identified in two probands with sporadic disease. In that their parents were neither clinically nor genetically affected, we conclude that mutations in each proband arose de novo. Transmission of the mutation and disease to an offspring occurred in one pedigree, predicting that these are germline mutations. The demonstration of hypertrophic cardiomyopathy arising within a pedigree coincident with the appearance of a de novo mutation provides compelling genetic evidence that beta cardiac MHC mutations cause this disease. We suggest that de novo mutations account for some instances of sporadic hypertrophic cardiomyopathy and that these mutations can be transmitted to children. The clinical benefits of defining mutations responsible for familial hypertrophic cardiomyopathy should also be available to some patients with sporadic disease.

Novel missense mutation in cardiac beta myosin heavy chain gene found in a Japanese patient with hypertrophic cardiomyopathy

We have analyzed the exon 9, 13, 14, 15, and 16 of cardiac beta myosin heavy chain gene in 96 Japanese patients with hypertrophic cardiomyopathy by using PCR-DNA conformation polymorphism analysis. The analysis revealed a sequence variation of the exon 16 in one patient. The sequence variation of a G to C transversion with replacement of Asn by Lys at the codon 615 was confirmed by sequencing and by dot-blot hybridization with an allele-specific oligonucleotide probe. Because the missense mutation was found at the residue conserved through birds to humans, this mutation was suggested to be a cause of hypertrophic cardiomyopathy in the patient. This is the first report of a mutant cardiac beta myosin heavy chain gene in the Japanese population.

Expression of a missense mutation in the messenger RNA for beta-myosin heavy chain in myocardial tissue in hypertrophic cardiomyopathy

We have determined that a missense mutation in exon 13 of the beta-myosin heavy chain (beta MHC) gene is expressed in the messenger RNA (mRNA) isolated from a right ventricular endomyocardial biopsy obtained from the proband of a family with hypertrophic cardiomyopathy. The mutation is the result of a substitution of an adenine for a guanine residue in one allele of the beta MHC gene and creates a second recognition site for the restriction endonuclease Ddel in exon 13. The mutation is inherited in a Mendelian fashion and co-segregates with hypertrophic cardiomyopathy in this family. Complementary DNAs synthesized from RNA isolated from the endomyocardial biopsy were cloned into a plasmid vector and sequenced to confirm the expression of both the normal and mutant allele in mRNA of myocardial tissue. This is the first report of the transcription of a mutant beta MHC gene allele into mRNA of the myocardium.