Identification of a mutation near a functional site of the beta cardiac myosin heavy chain gene in a family with hypertrophic cardiomyopathy

Genetic Association of Beta-Myosin Heavy-Chain Gene (MYH7) with Cardiac Dysfunction

Cardiac dysfunction accelerates the risk of heart failure, and its pathogenesis involves a complex interaction between genetic and environmental factors. Variations in myosin affect contractile abilities of cardiomyocytes and cause structural and functional abnormalities in myocardium. The study aims to find the association of MYH7 rs121913642 (c.1594 T>C) and rs121913645 (c.667G>A) variants with cardiac dysfunction in the Punjabi Pakistani population. Patients with heart failure (n = 232) and healthy controls (n = 205) were enrolled in this study. MYH7 variant genotyping was performed using tetra ARMS-PCR. MYH7 rs121913642 TC genotype was significantly more prevalent in the patient group (p < 0.001). However, MYH7 rs121913645 genotype frequencies were not significantly different between the patient and control groups (p < 0.666). Regression analysis also revealed that the rs121913642 C allele increases the risk of cardiac failure by ~2 [OR:1.98, CI: 1.31−2.98, p < 0.001] in comparison to the T allele. High levels of the cardiac enzymes cardiac troponin I (cTnI) and CK-MB were observed in patients. There was also an increase in total cholesterol, LDL cholesterol, and uric acid in patients compared to the healthy control group (p < 0.001). In conclusion, the MYH7 gene variant rs121913642 is genetically associated with cardiac dysfunction and involved in the pathogenesis of HF.

The genetic basis of hypertrophic cardiomyopathy in cats and humans

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

Identifying sarcomere gene mutations in hypertrophic cardiomyopathy: a personal history

This review provides an historical and personal perspective on the discovery of genetic causes for hypertrophic cardiomyopathy (HCM). Extraordinary insights by physicians who initially detailed remarkable and varied manifestations of the disorder, collaboration among multidisciplinary teams with skills in clinical diagnostics and molecular genetics, and hard work by scores of trainees solved the etiologic riddle of HCM and unexpectedly demonstrated mutations in sarcomere protein genes as the cause of disease. In addition to celebrating 20 years of genetic research in HCM, this article serves as an introductory overview to a thematic review series that will present contemporary advances in the field of hypertrophic heart disease. Through the continued application of advances in genetic methodologies, combined with biochemical and biophysical analyses of the consequences of human mutations, fundamental knowledge about HCM and sarcomere biology has emerged. Expanding research to elucidate the mechanisms by which subtle genetic variation in contractile proteins remodel the human heart remains an exciting opportunity, one with considerable promise to provide new strategies to limit or even prevent HCM pathogenesis.

Beta-myosin heavy chain gene mutations and hypertrophic cardiomyopathy in Austrian children

Hypertrophic cardiomyopathy occurs in two variants, either as an autosomal dominant familial disorder or as a sporadic disease without familial involvement. Different genes coding sarcomeric proteins of the heart have been identified as causing hypertrophic cardiomyopathy. Missense mutations in the cardiac beta-myosin heavy chain gene are found in 30% of all cases of familial hypertrophic cardiomyopathy. We screened the beta-myosin heavy chain gene of children of nine Austrian families with hypertrophic cardiomyopathy (referred to as group A) and of seven children with sporadic hypertrophic cardiomyopathy (referred to as group B). We were able to find two previously described (V606M, R453C) and two unknown missense mutations (V406M, R663H) in group A. Additionally, in two children of group B we could identify one already known missense mutation, R249Q as well as one previously unknown missense mutation, M877K. The genetically affected children of group A developed no or only mild clinical symptoms, whereas the children of group B with genetically confirmed sporadic hypertrophic cardiomyopathy showed manifest left ventricular hypertrophy and clinical symptoms including chest pain and dyspnoea. Clinical symptoms among the adults of group A, suffering from familial hypertrophic cardiomyopathy, varied significantly. We therefore believe V406M to be a more malignant missense mutation, probably linked with sudden death in the affected family, than R663H, which seems to be more benign causing late-onset hypertrophic cardiomyopathy and mild clinical symptoms in the affected family members.

Early expression of a malignant phenotype of familial hypertrophic cardiomyopathy associated with a Gly716Arg myosin heavy chain mutation in a Korean family

The clinical course and prognosis of familial hypertrophic cardiomyopathy (HCM) are different according to the type of mutation in the genes for sarcomere proteins. It has been disputed that a mutation, which occurs at a functionally important region in the sarcomere proteins, may increase the penetrance and expressivity of the disease. We searched for a causative mutation in an HCM family, which is characterized by early expression of clinical phenotype, high incidence of sudden death at young ages, and progressive heart failure in adults. Among the 32 family members in 4 generations, 13 were affected; 4 died suddenly before age 16, 2 children have already had full expression of the cardiac hypertrophy, and other adults have either progressive heart failure or poor left ventricular systolic functions. PCR-SSCP (polymerase chain reaction-single strand confirmation polymorphism) analysis of genomic DNAs isolated from peripheral blood leukocytes of the family members identified a Gly716Arg mutation in the cardiac beta-myosin heavy chain gene, which was cosegregated with the clinical phenotype. The mutation is localized near a functionally important site of the myosin heavy chain, the 2 active thiols, which contribute to the adenosine triphosphatase activity of myosin S1. This family provides further evidence that the mutation, which occurs at a functionally important site of the myosin heavy chain, is associated with the high penetrance and early expression of HCM.

Clinical features and prognostic implications of familial hypertrophic cardiomyopathy related to the cardiac myosin-binding protein C gene

BACKGROUND

Little information is available on phenotype-genotype correlations in familial hypertrophic cardiomyopathy that are related to the cardiac myosin binding protein C (MYBPC3) gene. The aim of this study was to perform this type of analysis.

METHODS AND RESULTS

We studied 76 genetically affected subjects from nine families with seven recently identified mutations (SASint20, SDSint7, SDSint23, branch point int23, Glu542Gln, a deletion in exon 25, and a duplication/deletion in exon 33) in the MYBPC3 gene. Detailed clinical, ECG, and echocardiographic parameters were analyzed. An intergene analysis was performed by comparing the MYBPC3 group to seven mutations in the beta-myosin heavy-chain gene (beta-MHC) group (n=52). There was no significant phenotypic difference among the different mutations in the MYBPC3 gene. However, in the MYBPC3 group compared with the beta-MHC group, (1) prognosis was significantly better (P<0.0001), and no deaths occurred before the age of 40 years; (2) the age at onset of symptoms was delayed (41+/-19 versus 35+/-17 years, P<0.002); and (3) before 30 years of age, the phenotype was particularly mild because penetrance was low (41% versus 62%), maximal wall thicknesses lower (12+/-4 versus 16+/-7 mm, P<0.03), and abnormal T waves less frequent (9% versus 45%, P<0.02).

CONCLUSIONS

These results are consistent with specific clinical features related to the MYBPC3 gene: onset of the disease appears delayed and the prognosis is better than that associated with the beta-MHC gene. These findings could be particularly important for the purpose of clinical management and genetic counseling in familial hypertrophic cardiomyopathy.

Diagnostic value of electrocardiography and echocardiography for familial hypertrophic cardiomyopathy in a genotyped adult population

BACKGROUND

The diagnostic value of ECG and echocardiography for familial hypertrophic cardiomyopathy (FHC) has not been reassessed since the development of molecular genetics. The aim of the study was to evaluate it in adults, with the genetic status used as the criterion of reference.

METHODS AND RESULTS

Ten families with previously identified mutations were studied (9 mutations in 3 genes). ECG and echocardiography were analyzed in 155 adults, of whom 77 were genetically affected and 78 unaffected. The major diagnostic criteria were, for echocardiography, a left ventricular wall thickness > 13 mm and, for ECG, abnormal Q waves, left ventricular hypertrophy, and marked ST-T changes. Minor ECG and echographic abnormalities were also analyzed. (1) Sensitivity and specificity of major criteria were 61% and 97% for ECG and 62% and 100% for echocardiography. (2) Sensitivity but not specificity was age related (from 50% at < 30 years to 94% at > 50 years old, P < .01) and sex related (83% in men versus 57% in women, P = .01). (3) Sensitivity was improved by the addition of minor criteria and by the association of ECG and echocardiography. The negative predictive value was therefore very good (95%) at > 30 years of age. (4) Healthy carriers without any ECG or echocardiographic abnormality represented 17% of genetically affected adults.

CONCLUSIONS

ECG and echocardiography have similar diagnostic values for FHC in adults, with an excellent specificity and a lower sensitivity. The association of the two techniques allows a better evaluation of the risk of being genetically affected in families with hypertrophic cardiomyopathy.

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.