Highlights
– Cohort-scale automated patch-clamp (APC) testing of 252 SCN5A missense/in-frame variants in a Brugada syndrome (BrS) cohort enabled reclassification of 110/225 variants of uncertain significance (VUS), mostly to likely pathogenic.
– Functional loss-of-function (LoF) severity correlated with anatomical localization (transmembrane pore regions), case enrichment, and penetrance; the most severe LoF variants (Z ≤ -6) had a ~24.5% penetrance and an odds ratio ~501 for BrS.
– A ClinGen/ACMG-calibrated multisite APC assay showed high inter-site concordance (R2=0.86 for peak INa) and produced odds-of-pathogenicity values supporting strong PS3/BS3 evidence for abnormal/normal function.
Background and clinical need
Brugada syndrome is an inherited arrhythmia syndrome associated with elevated risk of ventricular fibrillation and sudden cardiac death, typically manifesting as ST-segment elevation in the right precordial leads. Pathogenic loss-of-function variants in SCN5A, encoding the cardiac sodium channel NaV1.5, are the most widely recognized genetic contributors and explain roughly 20% of clinically ascertained BrS cases. However, variant interpretation is a major bottleneck: many missense variants are rare, display incomplete penetrance, and lack clear functional or segregation evidence. As a result, the majority of SCN5A missense variants in public databases (for example, ClinVar) remain classified as variants of uncertain significance (VUS), limiting their utility for diagnosis, cascade testing, and clinical decision-making.
Study designs and methods
Two complementary studies addressed these gaps using high-throughput automated patch-clamp (APC) functional assays calibrated to clinical variant-interpretation standards.
1) A cohort-scale APC study tested all 252 SCN5A missense and in-frame indel variants identified in a previously published BrS cohort of 3,335 patients. Each variant was assayed to generate an electrophysiological Z-score reflecting deviation from benign controls; thresholds were mapped to ACMG/AMP functional criteria (e.g., BS3_moderate for normal, PS3_strong for LoF). Functional data were integrated with population frequency (gnomAD), hotspot annotation, case-count enrichment, protein truncation/length changes, and in silico predictions to re-evaluate variant pathogenicity and estimate penetrance and odds ratios for BrS.
2) A multisite validation study independently ran an APC-based SCN5A-BrS assay at two centers (Vanderbilt University Medical Center and Victor Chang Cardiac Research Institute). The assay was calibrated using 49 high-confidence control variants and ClinGen Sequence Variant Interpretation (SVI) recommendations. Inter-site reproducibility was assessed (peak INa density R2=0.86). Odds-of-pathogenicity values were derived to support ClinGen-level evidence (PS3/BS3). The validated assay was then applied to several clinical VUS observed in families with BrS and related arrhythmia phenotypes.
Key results
Scale and functional outcomes. Of 252 tested variants, 146 (58%) were functionally abnormal (defined as Z ≤ -2) and 100 showed severe loss-of-function (Z ≤ -4). Abnormal variants clustered predominantly within transmembrane domains, especially pore-forming regions—consistent with channel gating and conductance impairments as primary disease mechanisms.
Reclassification impact. Integrating APC functional evidence with other ACMG criteria allowed reclassification of 110 of 225 previously VUS: 104 to likely pathogenic and 6 to likely benign. This represents a substantial reduction in diagnostic uncertainty for SCN5A in BrS cases and is likely to affect clinical management, family counseling, and cascade testing.
Penetrance and case enrichment. Quantitative relationships between functional severity and clinical effect emerged. Variants with extreme functional deficits (Z ≤ -6) had an estimated penetrance for BrS of 24.5% (95% CI 15.9%–37.7%) and an estimated odds ratio of ~501 for disease enrichment compared with population databases (gnomAD). Less severe functional changes showed correspondingly lower penetrance and odds ratios, demonstrating a graded, biologically plausible relationship between NaV1.5 dysfunction and clinical manifestation.
Multisite validation. The independent multisite assay validation showed strong correlation for key electrophysiologic parameters (e.g., peak INa density R2=0.86) and accurately separated known benign and pathogenic control variants (24/25 benign and 23/24 pathogenic concordant). Derived odds-of-pathogenicity values were 0.042 for normal function and 24.0 for abnormal function, supporting assignment of strong ACMG functional evidence codes (BS3 and PS3, respectively).
Clinical examples. In the multisite study, application of the calibrated assay to four clinical VUS identified loss-of-function for three variants, enabling their reclassification to likely pathogenic. These case-level changes illustrate how functional data can directly change patient-level genetic diagnosis and facilitate targeted family testing.
Expert commentary and interpretation
These studies collectively demonstrate that high-throughput, calibrated functional assays can supply clinical-grade evidence that meaningfully alters variant interpretation in SCN5A. Key strengths include cohort-scale coverage (testing all observed missense/in-frame variants in a large BrS cohort), ClinGen/ACMG-aligned calibration, and independent multisite validation confirming reproducibility.
From a mechanistic standpoint the concentration of pathogenic variants in transmembrane and pore regions is concordant with the expectation that structural perturbation of conduction pathways yields pronounced reductions in peak INa. The graded relationship between functional deficit and penetrance strengthens causal inference and provides a framework for probabilistic counseling: not all LoF variants carry equal risk.
Clinical impact is immediate. Reclassifying VUS to likely pathogenic enables cascade genetic testing, focused surveillance, and targeted risk-reduction strategies (for example, avoidance of sodium-channel blocking drugs and tailored lifestyle advice). Conversely, identifying normal-function ‘bystander’ variants reduces unnecessary anxiety and downstream interventions in carriers.
Limitations and caveats
Important limitations must be acknowledged. In vitro APC systems, although high-throughput and standardized, may not fully recapitulate cardiac cellular context: heterozygous expression, interacting accessory subunits (e.g., β-subunits), post-translational modifications, cellular trafficking, and tissue-specific regulatory mechanisms may modify variant effects in vivo. APC assays are typically performed at room temperature and in heterologous cell lines; temperature and cellular milieu can influence gating and kinetics.
Population databases have uneven ancestral representation; gnomAD-based frequency comparisons and penetrance estimates may mis-estimate risk in underrepresented groups. Incomplete clinical phenotyping and variable environmental modifiers also constrain direct genotype–phenotype mapping. Finally, some SCN5A variants can produce overlapping phenotypes (dilated cardiomyopathy, long QT, conduction disease), complicating single-phenotype penetrance estimates.
Clinical and research implications
For clinical laboratories and variant curation panels, these data support incorporation of well-calibrated APC functional evidence as strong ACMG-level criteria (PS3) when abnormal and BS3 when normal, provided assay validation steps are followed (controls, reproducibility, and calibration to ClinGen SVI guidance). The multisite validation demonstrates feasibility for decentralized clinical use and cross-center data pooling.
For clinicians, the findings provide a more granular framework for counseling: variant-specific functional severity now informs risk estimates and testing strategies for relatives. For patients with a newly reclassified likely pathogenic SCN5A variant, cascade testing can identify at-risk relatives who may require ECG screening, lifestyle counseling, or electrophysiology follow-up. Conversely, identification of normal-function variants can limit unnecessary interventions.
For researchers, remaining priorities include: performing heterozygous co-expression and cardiomyocyte (iPSC-derived) studies to refine context-dependent effects; expanding assays to capture trafficking and late/persistent current changes; and prospective genotype-driven cohorts to measure longitudinal clinical penetrance and modifier effects. Integration of high-throughput functional data into public resources (ClinVar, ClinGen) and variant effect maps will accelerate interpretation by the community.
Conclusions
High-throughput automated patch-clamp assays, when rigorously calibrated and validated across sites, provide robust, clinically actionable functional evidence for SCN5A variants. Cohort-scale functional phenotyping markedly reduces the burden of VUS in Brugada syndrome, quantifies a dose–response relationship between loss-of-function severity and penetrance, and supports stronger evidence-based genetic diagnosis, counseling, and cascade testing. Continued efforts to integrate functional datasets with clinical registries, ancestry-aware population data, and cell-type–specific models will further refine risk prediction and precision management in BrS.
Selected references
– O’Neill MJ, Ma JG, Aldridge JL, et al. Automated patch clamp data improve variant classification and penetrance stratification for SCN5A–Brugada syndrome. Eur Heart J. 2025 Nov 18:ehaf874. doi:10.1093/eurheartj/ehaf874. PMID: 41251004.
– Ma JG, O’Neill MJ, Richardson E, et al. Multisite Validation of a Functional Assay to Adjudicate SCN5A Brugada Syndrome–Associated Variants. Circ Genom Precis Med. 2024;17(4):e004569. doi:10.1161/CIRCGEN.124.004569. PMID: 38953211; PMCID: PMC11335442.
– Richards S, Aziz N, Bale S, et al. Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the ACMG and AMP. Genet Med. 2015;17(5):405–424.
– ClinGen Sequence Variant Interpretation Working Group recommendations (SVI) for functional assay interpretation and odds-of-pathogenicity calibration.
Funding and trial registration
Primary funding sources and study registration details are reported in the original publications (see references above).