Nonsense-mediated mRNA decay due to a CACNA1C splicing mutation in a patient with Brugada syndrome.

BACKGROUND: Brugada syndrome (BrS) is an inherited cardiac arrhythmia associated with sudden death due to ventricular fibrillation. Mutations in genes related to the cardiac L-type calcium channel have been reported to be causative of BrS. Generally, the messenger RNA (mRNA) that contains a nonsense mutation is rapidly degraded via its decay pathway, which is known as nonsense-mediated mRNA decay (NMD). Previously, we reported a male patient with BrS who carried c.1896G>A (the first nucleotide of CACNA1C exon 14), which caused a synonymous mutation, p.R632R.

OBJECTIVE: To examine how the synonymous CACNA1C mutation p.R632R produces the phenotype of BrS, with a special emphasis on the splicing error and NMD processes.

METHODS: We extracted mRNA from leukocytes of the proband and his 2 children and performed reverse transcription polymerase chain reaction. Complementary DNAs were checked by using direct sequencing and quantitative analysis.

RESULTS: The subsequent sequence electropherogram of the complementary DNAs did not show the substitution of the nucleotide identified in the genomic DNA of the proband. In the mRNA quantification analysis, we confirmed that reduction in the CACNA1C expression level was suspected to be caused by NMD.

CONCLUSIONS: Mutant mRNA with a c.1896G>A substitution may be diminished by NMD, and the resultant decrease in CACNA1C message leads to a novel mechanism for inducing BrS that is distinct from that reported previously.