Spectrum and prevalence of mutations involving BrS1- through BrS12-susceptibility genes in a cohort of unrelated patients referred for Brugada Syndrome genetic testing: Implications for genetic testing.

Objectives The aim of this study was to provide the spectrum and prevalence of mutations in the 12 Brugada syndrome (BrS)-susceptibility genes discovered to date in a single large cohort of unrelated BrS patients. Background BrS is a potentially lethal heritable arrhythmia syndrome diagnosed electrocardiographically by coved-type ST-segment elevation in the right precordial leads (V-1 to V-3; type 1 Brugada electrocardiographic [ECG] pattern) and the presence of a personal/family history of cardiac events. Methods Using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing, comprehensive mutational analysis of BrS1-through BrS12-susceptibility genes was performed in 129 unrelated patients with possible/probable BrS (46 with clinically diagnosed BrS [ECG pattern plus personal/family history of a cardiac event] and 83 with a type 1 BrS ECG pattern only). Results Overall, 27 patients (21%) had a putative pathogenic mutation, absent in 1,400 Caucasian reference alleles, including 21 patients with an SCN5A mutation, 2 with a CACNB2B mutation, and 1 each with a KCNJ8 mutation, a KCND3 mutation, an SCN1Bb mutation, and an HCN4 mutation. The overall mutation yield was 23% in the type 1 BrS ECG pattern-only patients versus 17% in the clinically diagnosed BrS patients and was significantly greater among young men <20 years of age with clinically diagnosed BrS and among patients who had a prolonged PQ interval. Conclusions We identified putative pathogenic mutations in similar to 20% of our BrS cohort, with BrS genes 2 through 12 accounting for <5%. Importantly, the yield was similar between patients with only a type 1 BrS ECG pattern and those with clinically established BrS. The yield approaches 40% for SCN5A-mediated BrS (BrS1) when the PQ interval exceeds 200 ms. Calcium channel-mediated BrS is extremely unlikely in the absence of a short QT interval

Characterization of <em>SEMA3A</em>-encoded semaphorin as a naturally occurring Kv4.3 protein inhibitor and its contribution to Brugada syndrome.

RATIONALE: Semaphorin 3A (SEMA3A)-encoded semaphorin is a chemorepellent that disrupts neural patterning in the nervous and cardiac systems. In addition, SEMA3A has an amino acid motif that is analogous to hanatoxin, an inhibitor of voltage-gated K channels. SEMA3A-knockout mice exhibit an abnormal ECG pattern and are prone to ventricular arrhythmias and sudden cardiac death. OBJECTIVE:: Our aim was to determine whether SEMA3A is a naturally occurring protein inhibitor of Kv4.3 (Ito) channels and its potential contribution to Brugada syndrome. METHODS AND RESULTS:: Kv4.3, Nav1.5, Cav1.2, or Kv4.2 were coexpressed or perfused with SEMA3A in HEK293 cells, and electrophysiological properties were examined via whole-cell patch clamp technique. SEMA3A selectively altered Kv4.3 by significantly reducing peak current density without perturbing Kv4.3 cell surface protein expression. SEMA3A also reduced Ito current density in cardiomyocytes derived from human-induced pluripotent stem cells. Disruption of a putative toxin binding domain on Kv4.3 was used to assess physical interactions between SEMA3A and Kv4.3. These findings in combination with coimmunoprecipitations of SEMA3A and Kv4.3 revealed a potential direct binding interaction between these proteins. Comprehensive mutational analysis of SEMA3A was performed on 198 unrelated SCN5A genotype-negative patients with Brugada syndrome, and 2 rare SEMA3A missense mutations were identified. The SEMA3A mutations disrupted SEMA3A&#39;s ability to inhibit Kv4.3 channels, resulting in a significant gain of Kv4.3 current compared with wild-type SEMA3A. CONCLUSIONS:: This study is the first to demonstrate SEMA3A as a naturally occurring protein that selectively inhibits Kv4.3 and SEMA3A as a possible Brugada syndrome susceptibility gene through a Kv4.3 gain-of-function mechanism

Variants in the 3&#39; untranslated region of the <em>KCNQ1</em>-encoded K_v7.1 potassium channel modify disease severity in patients with type 1 long QT syndrome in an allele-specific manner.

Aims Heterozygous mutations in KCNQ1 cause type 1 long QT syndrome (LQT1), a disease characterized by prolonged heart rate-corrected QT interval (QTc) and life-threatening arrhythmias. It is unknown why disease penetrance and expressivity is so variable between individuals hosting identical mutations. We aimed to study whether this can be explained by single nucleotide polymorphisms (SNPs) in KCNQ1&#39;s 3&#39; untranslated region (3&#39;UTR). Methods and results This study was performed in 84 LQT1 patients from the Academic Medical Center in Amsterdam and validated in 84 LQT1 patients from the Mayo Clinic in Rochester. All patients were genotyped for SNPs in KCNQ1&#39;s 3&#39;UTR, and six SNPs were found. Single nucleotide polymorphisms rs2519184, rs8234, and rs10798 were associated in an allele-specific manner with QTc and symptom occurrence. Patients with the derived SNP variants on their mutated KCNQ1 allele had shorter QTc and fewer symptoms, while the opposite was also true: patients with the derived SNP variants on their normal KCNQ1 allele had significantly longer QTc and more symptoms. Luciferase reporter assays showed that the expression of KCNQ1&#39;s 3&#39;UTR with the derived SNP variants was lower than the expression of the 3&#39;UTR with the ancestral SNP variants. Conclusion Our data indicate that 3&#39;UTR SNPs potently modify disease severity in LQT1. The allele-specific effects of the SNPs on disease severity and gene expression strongly suggest that they are functional variants that directly alter the expression of the allele on which they reside, and thereby influence the balance between proteins stemming from either the normal or the mutant KCNQ1 allele