Analysis of a Family with Brugada Syndrome and Sudden Cardiac Death Caused by a Novel Mutation of SCN5A

Abstract

Background: Brugada syndrome is a hereditary cardiac disease associated with mutations in ion channel genes. The clinical features include ventricular fibrillation, syncope, and sudden cardiac death. A family with Brugada syndrome with sudden cardiac death was analyzed to locate the associated mutation in the SCN5A gene.

Methods and results: Three generations of a Han Chinese family with Brugada syndrome were recruited in the study; their clinical phenotype data were collected and DNA samples extracted from the peripheral blood. Next-generation sequencing was carried out in the proband, and candidate genes and mutations were screened using the full exon capture technique. The family members who participated in the survey were tested for possible mutations using Sanger sequencing. Six family members were diagnosed with Brugada syndrome, including four asymptomatic patients. A newly discovered heterozygous mutation in the proband was located in exon 25 of SCN5A (NM_000335.5) at c.4313dup(p.Trp1439ValfsTer32). Among the surviving family members, only those with a Brugada wave on their electrocardiogram carried the c.4313dup(p.Trp1439ValfsTer32) variant. Bioinformatics prediction revealed that the frameshift of the c.4313dup (p.Trp1439ValfsTer32) mutant led to a coding change of 32 amino acids, followed by a stop codon, resulting in a truncated protein product.

Conclusion: The newly discovered mutation site c.4313dup(p.Trp1439ValfsTer32) in exon 25 of SCN5A may be the molecular genetic basis of the family with Brugada syndrome.

Figure 1

(a) Family map: black carries SCN5A (NM_000335.5) at c.4313dup (p.Trp1439ValfsTer32) mutation, the arrow is the proband, squares indicate males, and circles indicate females. (b) The proband (II1) 24 h ambulatory ECG: sinus rhythm; frequent ventricular extrasystole; intermittent first-degree atrioventricular block; intermittent abnormal ventricular repolarization (brugada wave in lead V1); continuous heart rate deceleration suggests moderate risk. (c) Sanger sequence diagram: c.4313dup (p.Trp1439ValfsTer32) mutant appeared in exon 25 of SCN5A gene. (d) Corresponding wild-type (WT).

Figure 2

(a) Routine ECG manifestations of I1: sinus rhythm; complete right bundle branch block (RBBB); ST segment elevation (V1, V2), Brugada-like changes; (b) routine ECG manifestations of II2: sinus rhythm; brugada wave; (c) routine ECG manifestations of II3: sinus rhythm; the V1 and V2 leads showed Brugada wave-like changes; (d) routine ECG manifestations of III 2: sinus rhythm; the V1 and V2 leads showed Brugada wave-like changes; (e) routine ECG manifestations of III4: sinus bradycardia; incomplete RBBB? brugada syndrome? ST segment elevation (II, III, and aVF).

Figure 3

SCN5A mRNA expression analysis using real-time qPCR. (a‒f) The SCN5A amplification and dissolution curves. (g, h) The SCN5A expression differences of WT members (n = 5) and p.Trp1439ValfsTer32 carriers (n = 10).

Figure 4

Tertiary structure of SCN5A WT and SCN5A c.4313dup (p.Trp1439ValfsTer32) mutant predicted using AlphaFold (https://alphafold.ebi.ac.uk/entry/Q14524) and shown in UCSF Chimera. (a) The blue region in SCN5A WT indicates the frameshift region resulting in 577 amino acids' deletion in p.Trp1439ValfsTer32 mutant. (b) The red region in SCN5A c.4313dup (p.Trp1439ValfsTer32) mutant (right) shows additional 32 amino acids caused by the frameshift.