Missense mutation of the beta-cardiac myosin heavy-chain gene in hypertrophic cardiomyopathy

Novel Mutations in β-MYH7 Gene in Indian Patients With Dilated Cardiomyopathy

Background

Methods

Results

Conclusions

Case Report: Identification of Mutations in LAMP2 in Two Chinese Infants With Danon Disease

Danon disease (DD) is a monogenic lysosomal storage disorder characterized by cardiomyopathy, skeletal myopathy, and variable degrees of intellectual disability. It is caused by a deficiency of lysosomal-associated membrane protein 2 (LAMP2). Two unrelated boys who presented with severe hypertrophic cardiomyopathy and elevated levels of liver enzymes, and were diagnosed with Danon disease at a very young age, were investigated. One boy was diagnosed at 4 months old and died soon after; his mother also died of hypertrophic cardiomyopathy shortly after his birth. Another developed hypertrophic cardiomyopathy at 3 months old but reported no significant cardiovascular symptoms during more than 5 years follow-up. Genetic screening found compound variants of LAMP2 and MYH7 in both of them. This report highlights the clinical heterogeneity in DD. The timely identification of LAMP2 mutation plays a critical role in their treatment and family counseling.

Identification of a novel hypertrophic cardiomyopathy-associated mutation using targeted next-generation sequencing

Hypertrophic cardiomyopathy (HCM), one of the most common forms of myocardial diseases, is the major cause of sudden cardiac death in young adults and competitive athletes. Analyses of gene mutations associated with HCM are valuable for its molecular diagnosis, genetic counseling, and management of familial HCM. To dissect the relationship between the clinical presentation and gene mutations of HCM, the genetic characterizations of 19 HCM-related genes in 18 patients (8 cases from 6 pedigrees with familial HCM and 10 cases without familial HCM) were detected using next-generation sequencing (NGS). As a result, 12 disease-related mutations were identified in the 18 subjects, including 6 single mutations and 3 double mutations [MYBPC3 (p.Gln998Glu) plus TNNI3 (p.Arg145Gly), PRKAG2 (p.Gly100Ser) plus MYBPC3 (p.Lys1209Serfs*28) and TNNI3 (p.Glu124Gln) plus GLA (p.Trp47*)]. The 3 heterozygous double mutations were discovered for the first time in the malignant familial HCM patients. Of the 6 single mutations, a novel mutation was found in tafazzin (TAZ, p.Ile208Val), and a mutation in β-myosin heavy chain gene (MYH7, p.Arg54Gln), which was reported as rare in the general population, was firstly found in one HCM patient. Identification of novel and rare mutations in HCM patients have added new data to the spectrum of gene mutations associated with this disease. These findings provide an essential basis for the molecular diagnosis and better management of family members at risk of familial HCM.

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.

Evaluation of the Mayo Clinic Phenotype-Based Genotype Predictor Score in Patients with Clinically Diagnosed Hypertrophic Cardiomyopathy

Genetic testing for hypertrophic cardiomyopathy (HCM) can provide an important clinical marker for disease outcome and family screening. This study set out to validate our recently developed phenotype-based HCM genotype predictor score. Patients clinically diagnosed with HCM and evaluated by genetic counselors comprised the study cohort. Genotype score was derived based on clinical and echocardiographic variables. Total score was correlated with the yield of genetic testing. Of 564 HCM patients, 198 sought genetic testing (35 %; 55 % male; mean age at diagnosis, 50 ± 20 years). Of these, 101 patients (51 %) were genotype positive for a HCM-associated genetic mutation (55 % male; mean age at diagnosis, 42 ± 18 years). Cochran-Armitage analysis showed similar, statistically significant trends of increased yields for higher genotype scores for both the original and study cohort. Validated by the current study, this scoring system provides an easy-to-use, clinical tool to aid in determining the likelihood of a positive HCM genetic test.

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.

A novel mutation of the beta myosin heavy chain gene responsible for familial hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disorder and shows high variability in genetic heterogeneity and phenotypic characteristics. The genetic etiology responsible for HCM in many individuals remains unclear.

OBJECTIVE

This instigation was sought to identify novel genetic determinants for familial hypertrophic cardiomyopathy.

METHODS

Six unrelated Chinese families with HCM were studied. For each of the 13 established HCM-susceptibility genes, 3 to 5 microsatellite markers were selected to perform genotyping and haplotype analysis. The linked genes were sequenced.

RESULTS

Haplotype analyses on candidate genetic loci revealed cosegregation of the gene beta-myosin heavy chain (MYH7) with HCM in a single family. A novel double heterozygous missense mutation of Ala26Val plus Arg719Trp in MYH7 was subsequently identified by sequencing in this family and was associated with a severe phenotype of HCM.

CONCLUSION

The novel double mutation of Ala26Val plus Arg719Trp in MYH7 identified in a Chinese family highlights the remarkable genetic heterogeneity of HCM, which provides important information for genetic counseling, accurate diagnosis, prognostic evaluation, and appropriate clinical management.

Regulation of vitamin D homeostasis: implications for the immune system

Vitamin D homeostasis in the immune system is the focus of this review. The production of both the activating (25- and 1alpha-hydroxylase) and the metabolizing (24-hydroxylase) enzymes by cells of the immune system itself, indicates that 1,25(OH)(2)D(3) can be produced locally in immune reaction sites. Moreover, the strict regulation of these enzymes by immune signals is highly suggestive for an autocrine/paracrine role in the immune system, and opens new treatment possibilities.

Familial aggregation of genetically heterogeneous hypertrophic cardiomyopathy: a boy with LEOPARD syndrome due to PTPN11 mutation and his nonsyndromic father lacking PTPN11 mutations

BACKGROUND

Nonsyndromic hypertrophic cardiomyopathy (HCM) is a primary cardiac disease transmitted as an autosomal dominant trait. Multiple chromosomal loci have been found to be involved in the etiology of this defect. LEOPARD syndrome is a genetic condition characteristically associated with HCM. Additional features of the syndrome include multiple lentigines, facial anomalies, sensorineural deafness, and growth retardation. Mutations in PTPN11, a gene encoding the protein tyrosine phosphatase SHP-2 located at chromosome 12q24, have been identified in patients with LEOPARD syndrome.

CASES

We report here on a patient with HCM presenting with classic clinical features of LEOPARD syndrome, whose father also has HCM, but lacks phenotypic anomalies of the syndrome. Molecular analysis searching for PTPN11 mutations was performed in this family. A missense mutation (836A-->G; Tyr279Cys) in exon 7 of PTPN11 gene was identified in the patient with LEOPARD syndrome, whereas no mutation in PTPN11 gene was detected in the father or in additional family members.

CONCLUSIONS

Aggregation of syndromic and nonsyndromic HCM in the same family is an unusual pattern of recurrence. Although genetic heterogeneity of LEOPARD and nonsyndromic HCM is not disputed, the existence of peculiar interactions linking genes causing nonsyndromic HCM and HCM in LEOPARD syndrome can be hypothesized. Different genes can work together, and a more severe cardiac phenotype can be due to additive effects. The involvement of familial susceptibility to specific cardiac malformations based on the presence of common predisposing factors can also be considered. Further molecular studies may shed light on these observations.

Heterologous expression of wild-type and mutant beta-cardiac myosin changes the contractile kinetics of cultured mouse myotubes

The properties of myosin expressed in muscle are a major determinant of muscle performance. In this study we used a novel approach to examine the functional impact of changes in myosin heavy chain (MHC) isoform expression, as well as the consequences of expressing the mutant MHC implicated in familial hypertrophic cardiomyopathy (FHC). Cultured mouse myoblasts that normally express fast embryonic myosin were untransfected, or stably transfected with a plasmid expressing either wild-type (cWT) or mutant (D778G or G741R) beta-cardiac myosin. After differentiation for 5-7 days, cWT or mutant beta-cardiac myosin was expressed at 25 % of total myosin in the myotube. We measured time-to-peak shortening (ttp), time for half-relaxation (t0.5), the maximum velocity of shortening (Vmax) at 1 Hz stimulation, and the tetanic fusion frequency. Expression of cWT beta-cardiac myosin significantly increased ttp and t0.5 and decreased the fusion frequency compared with untransfected myotubes. However, when we compared myotubes expressing mutant beta-cardiac myosin with those expressing cWT beta-cardiac myosin, we found that ttp and t0.5 were significantly decreased, and Vmax was increased for the D778G mutant, whereas ttp, t0.5 and Vmax were unchanged for the G741R mutant. The fusion frequency was increased for both mutant myosins. Our data support the conclusion that the impact of the slower myosin isoform dominates when both slow and fast isoforms are present. This work suggests that FHC associated with either D778G or G741R mutation in MHC is an 'energy cost' disease, but that the phenotype of D778G is more severe than that of G741R.

Variability in the ratio of mutant to wildtype myosin heavy chain present in the soleus muscle of patients with familial hypertrophic cardiomyopathy. A new approach for the quantification of mutant to wildtype protein

The ratio of mutant to wildtype myosin heavy chain (beta-isoform, beta-MHC) in the soleus muscle of patients with familial hypertrophic cardiomyopathy was determined by a combination of HPLC, mass spectrometry and capillary zone electrophoresis. In two patients, one with a Val 606 Met mutation and another with a Gly 584 Arg mutation, the fraction of mutant beta-MHC was only 12+/-6% and 23+/-0.7% of total beta-MHC, respectively. These results demonstrate the necessity to determine the ratio of mutant to wildtype protein for the interpretation of functional studies on biopsy material from heterozygous patients with an inherited disease.

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.

Verapamil therapy in infants with hypertrophic cardiomyopathy

We sought to evaluate the safety and efficacy of acute and chronic treatment with verapamil in infants with hypertrophic cardiomyopathy. Prior studies have shown an improvement in adults with hypertrophic cardiomyopathy who were treated with verapamil. Acutely, it reduced the degree of left ventricular outflow tract obstruction. Chronic therapy was associated with an improvement in symptoms and increased long-term survival. To date, no data are available on the efficacy of this drug in infants with hypertrophic cardiomyopathy. We evaluated prospectively the safety and efficacy of verapamil in infants. The acute and chronic effects of verapamil on infants with an echocardiographic diagnosis of hypertrophic cardiomyopathy were evaluated at a single institution between 1980 and 1994, with long-term follow-up available until 1996. Acute effects of an intravenous bolus of 0.1 mg/kg and infusion at 0.007 mg/kg/min were evaluated, where possible, in the cardiac catheterization laboratory. Oral verapamil at 3-5 mg/kg/day was started after catheterization. Follow-up included serial clinical, echocardiographic and Holter monitoring. A total of 22 patients were studied, 17 having a presumed diagnosis of primary hypertrophic cardiomyopathy including three with Noonan's syndrome. Acute infusion of the drug was well tolerated by all, without adverse electrophysiological effects. Haemodynamic effects were consistent with a negative inotropic action with significant falls in cardiac index (4.6+/-1.2 to 4.1+/-0.9 l/min/m2), systolic blood pressure (88+/-16 to 82+/-14 mmHg) and gradient across the left ventricular outflow tract (nine patients 48.2+/-30.4 to 28.4+/-24.1 mmHg). End-diastolic pressure was unchanged (14.0+/-6.8 to 13.9+/-4.7 mmHg). Three patients with primary hypertrophic cardiomyopathy died (two while being treated). In the group with primary hypertrophic cardiomyopathy continuing with long-term treatment, follow-up revealed regression in two, progression in three (two died) and stability in 10. For those treated, there was a trend towards improvement in clinical status. Verapamil is well tolerated acutely in infants with hypertrophic cardiomyopathy. The outcome was considerably better in these patients compared with prior reports, though careful long-term assessment is needed.

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.