Fatal neonatal hypertrophic cardiomyopathy caused by compound heterozygous truncating MYBPC3 mutation

Novel pathogenic variant of MYBPC3 responsible for hypertrophic cardiomyopathy

OBJECTIVES

This study aims to investigate the pathogenic gene variant in a family with hypertrophic cardiomyopathy by using whole-exome sequencing and to explore the relationship between the gene variant and clinical phenotype.

METHODS

Peripheral blood was collected from a family with hypertrophic cardiomyopathy, and deoxyribonucleic acid was extracted. The possible pathogenic genes were detected by whole-exome sequencing, and the variant was verified by Sanger sequencing. Functional change in the variant was predicted by bioinformatics software. Clinical data of the family members are analysed simultaneously.

RESULTS

The proband carries a novel heterozygous nonsense variant of MYBPC3:c.2731G > T (p.E911X). The analysis of amino acid conservation suggests that the variation is highly conserved. The three-dimensional protein structure shows that the variant in MYBPC3 results in the incompleteness of the fibronectintype-III2 (p872-967) domain and deletion of Ig-like C2-type 6 (p971-1065) and fibronectin type-III 3 and Ig-like C2-type 7 (p1181-1274) domains, in which p1253-1268 is predicted to have a transmembrane helix structure. Clinical data indicate that the phenotypes of variant carriers with hypertrophic cardiomyopathy are diverse, suggesting the functional damages to the protein of MYBPC3.

CONCLUSION

The phenotypes of variant carriers with hypertrophic cardiomyopathy caused by the novel variant in MYBPC3: c.2731G > T (p.E911X) exhibit variable severity and clinical manifestations. Whole-exome sequencing can be used to comprehensive screen hypertrophic cardiomyopathy genes and provide a strong basis for early screening and accurate diagnosis and treatment of hypertrophic cardiomyopathy in children.

Targeting the population for gene therapy with MYBPC3

Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited myocardial disease characterized by unexplained left ventricular hypertrophy, diastolic dysfunction and myocardial disarray. Clinical heterogeneity is wide, ranging from asymptomatic individuals to heart failure, arrhythmias and sudden death. HCM is often caused by mutations in genes encoding components of the sarcomere. Among them, MYBPC3, encoding cardiac myosin-myosin binding protein C is the most frequently mutated gene. Three quarter of pathogenic or likely pathogenic mutations in MYBPC3 are truncating and the resulting protein was not detected in HCM myectomy samples. The overall prognosis of the patients is excellent if managed with contemporary therapy, but still remains a significant disease-related health burden, and carriers with double heterozygous, compound heterozygous and homozygous mutations often display a more severe clinical phenotype than single heterozygotes. We propose these individuals as a good target population for MYBPC3 gene therapy.