Functional Characterization of a Novel MYBPC3 Splice-Altering Variant Identified in a Chinese Patient with Hypertrophic Cardiomyopathy

Background: Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous myocardial disorder in which variants in MYBPC3 represent a major genetic cause, although the functional significance of newly identified splice-region variants often remains uncertain. Methods: We investigated a previously unreported heterozygous MYBPC3 variant, NM_000256.3: c.2414-6_2421del, identified by whole-exome sequencing in a Chinese male patient with HCM and cardiac dysfunction. Adenoviral vectors expressing wild-type (Ad-WT) or mutant (Ad-MUT) MYBPC3 were used to establish cardiomyocyte models. Results: Compared with Ad-WT cells, Ad-MUT cells showed increased ANP and BNP expression, enhanced ERK phosphorylation, and cytoskeletal alterations assessed by phalloidin staining, indicating a hypertrophic cellular response. Three region-specific RT-qPCR assays demonstrated reduced MYBPC3 transcript abundance in Ad-MUT cells, with a greater reduction in the exon 25–26-spanning amplicon, suggesting altered RNA processing involving the variant-adjacent region. Cycloheximide treatment increased the abundance of mutant-associated transcripts, supporting their degradation through nonsense-mediated mRNA decay. Conclusions: MYBPC3 c.2414-6_2421del disrupts transcript processing and promotes nonsense-mediated mRNA decay (NMD)-associated transcript depletion, accompanied by cardiomyocyte hypertrophic remodeling. These findings provide functional evidence relevant to the interpretation of this previously unreported variant in HCM.