Recent advances in genetics and treatment of hypertrophic cardiomyopathy

Screening of MYH7 gene mutation sites in hypertrophic cardiomyopathy and its significance

BACKGROUND

There have been few reports of mutations in the beta-myosin heavy chain (MYH7) gene in hypertrophic cardiomyopathy (HCM), which is associated with sudden cardiac death caused by HCM. This study aimed to screen the mutation sites in the sarcomeric gene MYH7 in Chinese patients with HCM. We also planned to analyze the pathogenicity of the mutation site as well as its significance in clinical and forensic medicine.

METHODS

From January 2006 to June 2017, autopsy cases were collected from the Department of Pathology, the Affiliated Hospital of Qingdao University. The experiment was to detect MYH7 gene status in formalin-fixed paraffin-embedded tissues from 18 independent autopsy cases who suffered HCM related sudden death (fatal HCM) and 20 cases without cardiomyopathy. Common mutation exon fragments of MYH7 gene were amplified by polymerase chain reaction. The end-of-deoxygenation method and gene cloning method were further performed to analyze the mutation sites. Homologous comparison among mutant sites was conducted using BLAST online database.

RESULTS

The 1336th nucleotide of MYH7 gene at exon 14 was converted from T to G in one HCM case, resulting in the conversion of threonine (Thr) at position 446 to proline (Pro). In another case, the 1402th nucleotide at exon 14 was converted from T to C, resulting in the conversion of phenylalanine (Phe) at position 468 to leucine (Leu). Homologous comparison results showed that the two amino acid residues of Thr446 and Phe468 are highly conserved among different species.

CONCLUSIONS

Our results showed fatal HCM harbored mutations of Thr446Pro and Phe468Leu in the MYH7 gene. It is significant for clinical and forensic medicine to further explore the functions and detailed mechanisms of these mutations.

Antifibrotic effects of antioxidant N-acetylcysteine in a mouse model of human hypertrophic cardiomyopathy mutation

OBJECTIVES

The objective was to determine the effects of antioxidant N-acetylcysteine (NAC) on reversal and attenuation of established interstitial fibrosis in the cardiac troponin T (cTnT) mouse model of human hypertrophic cardiomyopathy (HCM) mutation.

BACKGROUND

Interstitial fibrosis is a characteristic pathological feature of HCM and a risk factor for sudden cardiac death. The cTnT-Q92 transgenic mice, generated by cardiac-restricted expression of human HCM mutation, show a two- to four-fold increase in interstitial fibrosis.

METHODS

We randomized the cTnT-Q92 mice to treatment with a placebo or NAC (250, 500, or 1,000 mg/kg/day) and included non-transgenic mice as controls (N = 5 to 13 per group). We performed echocardiography before and 24 weeks after therapy, followed by histologic and molecular characterization.

RESULTS

There were no significant differences in the baseline characteristics of the groups. Treatment with NAC reduced myocardial concentrations of malondialdehyde and 4-hydroxy-2(E)-nonenal, markers of oxidative stress, by 40%. Collagen volume fractions comprised 1.94 +/- 0.76% of the myocardium in non-transgenic, 6.2 +/- 1.65% in the placebo, and 1.56 +/- 0.98% in the NAC (1,000 mg/kg/day) groups (p < 0.001). Expression levels of Col1a1 and Col1a2 were also reduced significantly, as were levels of phosphorylated but not total p44/42, p38, and c-Jun NH2-terminal kinase. Levels of oxidized mitochondrial and nuclear DNA were not significantly different.

CONCLUSIONS

Treatment with NAC reduced myocardial oxidative stress, stress-responsive signaling kinases, and fibrosis in a mouse model of HCM. The potential beneficial effects of NAC in reversal of cardiac phenotype in human HCM, the most common cause of sudden cardiac death in the young, merits investigation.