Differences in clinical expression of hypertrophic cardiomyopathy associated with two distinct mutations in the beta-myosin heavy chain gene. A 908Leu----Val mutation and a 403Arg----Gln mutation

Presence of human T-lymphotropic virus type II-related genes in DNA of peripheral leukocytes from patients with autoimmune thyroid diseases

No etiologic role of human T-lymphotropic virus type II (HTLV-II) in any disease is yet known. The present study showed a high incidence of HTLV-II proviral DNA fragments in DNA of peripheral blood leukocytes from patients with autoimmune thyroid diseases. Using primers for the pol and tax regions of HTLV-II proviral DNA, amplified DNA fragments were demonstrated in 51.5% of the patients with Hashimoto's thyroiditis and in 11.8% of those with Graves' disease examined, but in only 1.9% of the disease controls and 1.0% of healthy individuals. These amplified DNA fragments hybridized with each of the inner probes. The nucleotide sequences of the DNA fragments of the pol and tax regions showed high homology with those of the prototype of HTLV-II. No antibodies for HTLV-II could, however, be detected in the patients examined. Because of the absence of its antibody, HTLV-II infection was not confirmed in these patients, but the presence of HTLV-II proviral DNA or its related DNA at high frequency suggests a relationship of HTLV-II with the development of autoimmune thyroid diseases.

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.

The electrocardiogram is a more sensitive indicator than echocardiography of hypertrophic cardiomyopathy in families with a mutation in the MYH7 gene

BACKGROUND

Mutations in the cardiac beta myosin heavy chain gene causing hypertrophic cardiomyopathy have been identified, and to assist both diagnosis and prediction of outcome attempts have been made to correlate phenotype and genotype. Two new mutations in codon 403 of the gene in three unrelated families are described and attention drawn to variable or even absent phenotypic expression in different family members.

METHODS AND RESULTS

The polymerase chain reaction and heteroduplex analysis on Mutation Detection Enhancement gels were used to search for mutations in the globular head of the beta myosin heavy chain gene in families with hypertrophic cardiomyopathy. Two mutations were found in exon 13 (codon 403) of the gene. In two unrelated Polish families the mutation resulted in the conversion of arginine to tryptophan (CGG: >TGG). A second mutation, found in a British family, converted the same arginine to leucine (CGG: >CTG). These mutations were detected in family members who had electrocardiographic and echocardiographic features typical of hypertrophic cardiomyopathy; however, they were also detected in 7 other adult relatives with an abnormal electrocardiogram but a normal echocardiogram. Two unrelated adult relatives had completely normal clinical findings but carried the gene mutation.

CONCLUSIONS

Identification of a specific mutation gives no guide to the clinical phenotype. There is considerable variability in the phenotypic expression of hypertrophic cardiomyopathy. Mutations were detected in adults previously regarded as normal or in whom the diagnosis was questionable. The fact that the clinical significance of the mutation in these people is still unknown emphasises the dilemma facing screening programmes. Isolated, unexplained electrocardiographic abnormalities in first degree relatives in a family with a definitive diagnosis of hypertrophic cardiomyopathy should be regarded as evidence of a carrier state.

Prognostic implications of novel beta cardiac myosin heavy chain gene mutations that cause familial hypertrophic cardiomyopathy

Three novel beta cardiac myosin heavy chain (MHC) gene missense mutations, Phe513Cys, Gly716Arg, and Arg719Trp, which cause familial hypertrophic cardiomyopathy (FHC) are described. One mutation in exon 15 (Phe513Cys) does not alter the charge of the encoded amino acid, and affected family members have a near normal life expectancy. The Gly716Arg mutation (exon 19; charge change of +1) causes FHC in three family members, one of whom underwent transplantation for heart failure. The Arg719Trp mutation (exon 19; charge change of -1) was found in four unrelated FHC families with a high incidence of premature death and an average life expectancy in affected individuals of 38 yr. A comparable high frequency of disease-related deaths in four families with the Arg719Trp mutation suggests that this specific gene defect directly accounts for the observed malignant phenotype. Further, the significantly different life expectancies associated with the Arg719Trp vs. Phe513Cys mutation (P < 0.001) support the hypothesis that mutations which alter the charge of the encoded amino acid affect survival more significantly than those that produce a conservative amino acid change.

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.

Prognosis in hypertrophic cardiomyopathy observed in a large clinic population

Overall annual cardiac mortality in hypertrophic cardiomyopathy (HC) has been reported to be between 2 and 4%, although these numbers are primarily from retrospective studies of patients referred to large research institutions. A clinic population of 113 patients with HC was prospectively studied to assess cardiac mortality in the overall group and in selected subgroups commonly thought to be at high risk for sudden death. The mean age at diagnosis was 37 +/- 16 years. During follow-up, there were 11 cardiac and 2 noncardiac deaths. The annual cardiac mortality was 1% (95% confidence interval 0.2-1.8%). Because of the small number of deaths, relative risk for cardiac death was not significantly different in the presence of young age (< or = 30 years), family history of HC and sudden death, history of syncope or previous cardiac arrest, or both, ventricular tachycardia on 24-hour Holter monitoring, or septal myotomy/myectomy for refractory symptoms and outflow tract obstruction. It is concluded that HC has a relatively benign prognosis (1% annual cardiac mortality) that is 2 to 4 times less than that previously reported.

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.

A familial hypertrophic cardiomyopathy locus maps to chromosome 15q2

We report that a gene responsible for familial hypertrophic cardiomyopathy (FHC) in a kindred with a mild degree of cardiac hypertrophy maps to chromosome 15q2. The gene encoding cardiac actin, located on chromosome 15q, was analyzed and excluded as a candidate for FHC at this locus. Two additional families with typical FHC were studied and the disorder in one also maps to the chromosome 15q2 locus. The maximum combined multipoint logarithm of odds score in the two linked families is 6.02. Although these two kindreds reside in the same country, we believe that their disorder is caused by independent mutations in the 15q2 locus because of the clinical and genotypic differences between affected individuals. Mutations in at least four loci can cause FHC: chromosomes 14q1 (beta cardiac myosin heavy chain gene), 1q3, and 15q2 and another unidentified locus, suggesting substantial genetic heterogeneity.

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.

A disease locus for familial hypertrophic cardiomyopathy maps to chromosome 1q3

Familial hypertrophic cardiomyopathy (FHC) is caused by missense mutations in the beta cardiac myosin heavy chain (MHC) gene in less than half of affected individuals. To identify the location of another gene involved in this disorder, a large family with FHC not linked to the beta MHC gene was studied. Linkage was detected between the disease in this family and a locus on chromosome 1q3 (maximum multipoint lod score = 8.47). Analyses in other families with FHC not linked to the beta MHC gene, revealed linkage to the chromosome 1 locus in two and excluded linkage in six. Thus mutations in at least three genetic loci can cause FHC. Three sarcomeric contractile proteins--troponin I, tropomyosin and actin--are strong candidate FHC genes at the chromosome 1 locus.