SCN3B is supported as a candidate gene for Brugada syndrome with an overall Limited gene-disease association. The supplied evidence is most consistent with an autosomal dominant susceptibility model for SCN3B-associated Brugada syndrome, but the human evidence remains based on a small number of unrelated probands and limited segregation data PMID:19606473, PMID:20031595, PMID:23257389, PMID:38450374, PMID:39761910.
Human genetic support for SCN3B in Brugada syndrome includes a white male with drug-provoked type 1 Brugada ECG carrying c.29T>C (p.Leu10Pro), identified after sequencing known Brugada syndrome genes and reported absent from 296 controls PMID:20031595. A Japanese/Korean SCN5A-negative cohort found c.328G>A (p.Val110Ile) in 3 of 178 Japanese probands and not in 480 controls, providing the strongest recurrence signal for SCN3B in the supplied dataset PMID:23257389. Additional single-patient reports described c.260C>T (p.Pro87Leu) in a Chinese Brugada syndrome pedigree and c.412_414del (p.Thr138del) in a 54-year-old man with spontaneous type 1 Brugada ECG, palpitations, and vertigo/dizziness PMID:38450374, PMID:39761910.
Reported SCN3B variant classes are predominantly rare missense changes and one in-frame single-codon deletion: c.29T>C (p.Leu10Pro), c.260C>T (p.Pro87Leu), c.328G>A (p.Val110Ile), and c.412_414del (p.Thr138del) PMID:20031595, PMID:23257389, PMID:38450374, PMID:39761910. SCN3B c.328G>A (p.Val110Ile) appears recurrent in Japanese patients, whereas other SCN3B variants were each reported once in the supplied Brugada syndrome evidence PMID:23257389. The SCN3B gene has also had other variants mentioned in broader population or sudden death studies, including c.58A>G (p.Ser20Gly), c.583G>A (p.Ala195Thr), and c.29T>C (p.Leu10Pro), but in those contexts the data either did not establish Brugada syndrome causality or treated the variants as uncertain PMID:27711072, PMID:24529773, PMID:25757662.
The Brugada syndrome phenotype linked to SCN3B in the supplied evidence centers on spontaneous or provoked type 1 Brugada ECG and ventricular arrhythmia risk, with some SCN3B-positive individuals presenting with palpitations, vertigo/dizziness, or ventricular arrhythmia-related manifestations PMID:20031595, PMID:23257389, PMID:39761910. The SCN3B gene was discussed in a mutation update noting that Brugada syndrome overall usually shows autosomal dominant inheritance with reduced penetrance and variable expressivity, but the SCN3B-specific pedigrees and segregation information were not robustly detailed in the supplied dataset PMID:19606473.
Functional data for SCN3B are a relative strength of this association. SCN3B c.29T>C (p.Leu10Pro) caused an 82.6% reduction in peak sodium current, altered inactivation/reactivation, and impaired trafficking of Nav1.5 to the cell surface in heterologous cells PMID:20031595. SCN3B c.328G>A (p.Val110Ile) reduced sodium current and decreased cell-surface Nav1.5 expression PMID:23257389. SCN3B c.260C>T (p.Pro87Leu) reduced peak sodium current by about 60% and decreased membrane localization of both SCN3B and SCN5A, and SCN3B c.412_414del (p.Thr138del) reduced peak current and channel availability with heterozygous-like accelerated fast inactivation, despite preserved surface expression and interaction with Nav1.5 PMID:38450374, PMID:39761910. Across these studies, SCN3B functional findings are concordant with a loss-of-function effect on the cardiac sodium channel complex.
Important limitations weaken the clinical validity of SCN3B for Brugada syndrome. A Dutch cohort of 38 SCN5A-negative Brugada syndrome probands found no SCN3B mutations, arguing that SCN3B is unlikely to be a major causal gene in that population PMID:17556197. A Danish/Iranian screening study of 42 Brugada syndrome patients found no SCN3B mutations and specifically noted that exome frequency data made prior SCN3B associations less likely PMID:22284586. A population-based study further reported that some previously cataloged Brugada syndrome variants, including SCN3B c.58A>G (p.Ser20Gly) and c.328G>A (p.Val110Ile), were observed in the general population without type 1 Brugada ECG or excess arrhythmic outcomes, highlighting variant-level and gene-level uncertainty PMID:27711072. No conflicting evidence was provided that fully refutes SCN3B, but the available data do indicate incomplete replication and uncertain penetrance.
In aggregate, the SCN3B gene has plausible disease biology, several rare variants with concordant sodium-channel loss-of-function effects, and a small number of Brugada syndrome probands across independent reports PMID:20031595, PMID:23257389, PMID:38450374, PMID:39761910. However, SCN3B lacks strong segregation evidence in the supplied material, includes variants later seen in population datasets, and has negative cohort studies that argue against SCN3B as a frequent monogenic cause of Brugada syndrome PMID:17556197, PMID:22284586, PMID:27711072. Key take-home: SCN3B is a biologically credible but still limited-evidence Brugada syndrome gene, so SCN3B variants should be interpreted cautiously and generally require strong variant-level evidence and phenotype correlation before use in clinical decision-making.
Gene–Disease AssociationLimitedA small number of unrelated Brugada syndrome probands with SCN3B variants and supportive in vitro loss-of-function data, but minimal segregation and several negative or cautionary cohort/population studies. Genetic EvidenceLimitedSingle-case reports plus one recurrent Japanese variant in 3 probands support SCN3B, but segregation is lacking and broader cohort studies did not consistently replicate the association. Functional EvidenceModerateMultiple independent SCN3B variants reduce sodium current and/or impair Nav1.5 trafficking in heterologous systems, supporting a consistent loss-of-function mechanism. |