Genetic variations of β-MYH7 in hypertrophic cardiomyopathy and dilated cardiomyopathy.

CONTEXT: Hypertrophic cardiomyopathy (HCM) is known to be manifested by mutations in 12 sarcomeric genes and dilated cardiomyopathy (DCM) is known to manifest due to cytoskeletal mutations. Studies have revealed that sarcomeric mutations can also lead to DCM. Therefore, in the present study, we have made an attempt to compare and analyze the genetic variations of beta-myosin heavy chain gene (β-MYH7), which are interestingly found to be common in both HCM and DCM. The underlying pathophysiological mechanism leading to two different phenotypes has been discussed in this study. Till date, about 186 and 73 different mutations have been reported in HCM and DCM, respectively, with respect to this gene. AIM: The screening of β-MYH7 gene in both HCM and DCM has revealed some common genetic variations. The aim of the present study is to understand the pathophysiological mechanism underlying the manifestation of two different phenotypes. MATERIALS AND METHODS: 100 controls, 95 HCM and 97 DCM samples were collected. Genomic DNA was extracted following rapid nonenzymatic method as described by Lahiri and Nurnberger (1991), and the extracted DNA was later subjected to polymerase chain reaction (PCR) based single stranded conformation polymorphism (SSCP) analysis to identify single nucleotide polymorphism (SNP)s/mutations associated with the diseased phenotypes. RESULTS AND CONCLUSION: Similar variations were observed in β-MYH7 exons 7, 12, 19 and 20 in both HCM and DCM. This could be attributed to impaired energy compromise, or to dose effect of the mutant protein, or to even environmental factors/modifier gene effects wherein an HCM could progress to a DCM phenotype affecting both right and left ventricles, leading to heart failure.

Epidemiology and genetics of hypertrophic cardiomyopathy.

Background: Hypertrophic cardiomyopathy (HCM) is a heart muscle disorder and is known to be inherited as an autosomal dominant trait. Mutations in several sarcomeric, cytoskeletal and mitochondrial genes have been reported in HCM. Though many cases of HCM are being identified, there is limited data regarding the epidemiology and genetics of HCM in India. Aim: Therefore the present study is envisaged at identifying the epidemiological variables in HCM and fitting a probability model assuming dominant mode of inheritance in HCM, which may in turn shed light on the heterogeneity of this complex disorder. Materials AND Methods: The 127 HCM cases were divided into subtypes based on pattern of hypertrophy. Chi square analysis, odds ratio, probability, relative frequency, penetrance and heritability estimates were calculated apart from epidemiological variables. Results: The HCM subtypes revealed the heterogeneous nature of the condition suggesting that the genes/mutations involved in their pathogenesis are different and this is supported by distinctive differences observed in their probability, heritability and penetrance estimates apart from epidemiological variables. An increased male preponderance was observed with the sex ratio being 3.7:1. The age at onset was found to be more than a decade early in familial cases (30 ± 10 yrs) compared to non familial cases (44 ± 14 yrs). Chi square analysis revealed obstructive HCM to be following autosomal dominant mode of inheritance where as non-obstructive HCM was significantly deviating. The level of deviation was significantly high for the middle onset group compared to early and late onset groups, therefore this group may be considered as an admixture wherein genes/gene modifiers and environmental variables may be contributing to the heterogeneity and this is further supported by odds ratio. Conclusions: The study thus brings out the complexity of HCM and suggests that modes of inheritance other than autosomal dominant may be encountered in a subset of HCM especially in asymmetric septal hypertrophy, apical, concentric and mid cavity obstruction subsets and hence a mixed model of inheritance is the best fit for such complex disorders.