Atrioventricular nodal reentrant tachycardia (AVNRT) may coexist with Brugada syndrome (BrS).
The present study was designed to determine the prevalence of drug-induced type 1 Brugada ECG pattern ...(concealed BrS) in patients presenting with clinical spontaneous AVNRT and to investigate their electrocardiographic, electrophysiological, and genetic characteristics.
Ninety-six consecutive patients without any sign of BrS on baseline electrocardiogram undergoing electrophysiological study and ablation for symptomatic, drug-resistant AVNRT and 66 control subjects underwent an ajmaline challenge to unmask BrS. Genetic screening was performed in 17 patients displaying both AVNRT and BrS.
A concealed BrS electrocardiogram was uncovered in 26 of 96 patients with AVNRT (27.1%) and in 3 of 66 control subjects (4.5%) (P ≤ .001). Patients with concealed BrS were predominantly female patients (n=23 88.5% vs n=44 62.9%, P = .015), had higher prevalence of chest pain (n=10 38.5% vs n=13 18.6%, p=0.042), migraine headaches (n=10 38.5% vs n=10 14.2%, p=0.008), and drug-induced initiation and/or worsening of duration and/or frequency of AVNRT (n=4 15.4% vs n=1 1.4%, p=0.006) as compared to patients with AVNRT without BrS. Genetic screening identified 19 mutations or rare variants in 13 genes in 13 of 17 patients with both AVNRT and BrS (yield = 76.5%). Ten of these 13 genotype-positive patients (76.9%) harbored genetic variants known or suspected to cause a loss of function of cardiac sodium channel current (SCN5A, SCN10A, SCN1B, GPD1L, PKP2, and HEY2).
Our results suggest that spontaneous AVNRT and concealed BrS co-occur, particularly in female patients, and that genetic variants that reduce sodium channel current may provide a mechanistic link between AVNRT and BrS and predispose to expression of both phenotypes.
Cardiac ion channelopathies are responsible for an ever-increasing number and diversity of familial cardiac arrhythmia syndromes. We describe a new clinical entity that consists of an ST-segment ...elevation in the right precordial ECG leads, a shorter-than-normal QT interval, and a history of sudden cardiac death.
Eighty-two consecutive probands with Brugada syndrome were screened for ion channel gene mutations with direct sequencing. Site-directed mutagenesis was performed, and CHO-K1 cells were cotransfected with cDNAs encoding wild-type or mutant CACNB2b (Ca(v beta2b)), CACNA2D1 (Ca(v alpha2delta1)), and CACNA1C tagged with enhanced yellow fluorescent protein (Ca(v)1.2). Whole-cell patch-clamp studies were performed after 48 to 72 hours. Three probands displaying ST-segment elevation and corrected QT intervals < or = 360 ms had mutations in genes encoding the cardiac L-type calcium channel. Corrected QT ranged from 330 to 370 ms among probands and clinically affected family members. Rate adaptation of QT interval was reduced. Quinidine normalized the QT interval and prevented stimulation-induced ventricular tachycardia. Genetic and heterologous expression studies revealed loss-of-function missense mutations in CACNA1C (A39V and G490R) and CACNB2 (S481L) encoding the alpha1- and beta2b-subunits of the L-type calcium channel. Confocal microscopy revealed a defect in trafficking of A39V Ca(v)1.2 channels but normal trafficking of channels containing G490R Ca(v)1.2 or S481L Ca(v beta2b)-subunits.
This is the first report of loss-of-function mutations in genes encoding the cardiac L-type calcium channel to be associated with a familial sudden cardiac death syndrome in which a Brugada syndrome phenotype is combined with shorter-than-normal QT intervals.
L-type calcium channel (LTCC) mutations have been associated with Brugada syndrome (BrS), short QT (SQT) syndrome, and Timothy syndrome (LQT8). Little is known about the extent to which LTCC ...mutations contribute to the J-wave syndromes associated with sudden cardiac death.
The purpose of this study was to identify mutations in the α1, β2, and α2δ subunits of LTCC (Ca(v)1.2) among 205 probands diagnosed with BrS, idiopathic ventricular fibrillation (IVF), and early repolarization syndrome (ERS). CACNA1C, CACNB2b, and CACNA2D1 genes of 162 probands with BrS and BrS+SQT, 19 with IVF, and 24 with ERS were screened by direct sequencing.
Overall, 23 distinct mutations were identified. A total of 12.3%, 5.2%, and 16% of BrS/BrS+SQT, IVF, and ERS probands displayed mutations in α1, β2, and α2δ subunits of LTCC, respectively. When rare polymorphisms were included, the yield increased to 17.9%, 21%, and 29.1% for BrS/BrS+SQT, IVF, and ERS probands, respectively. Functional expression of two CACNA1C mutations associated with BrS and BrS+SQT led to loss of function in calcium channel current. BrS probands displaying a normal QTc had additional variations known to prolong the QT interval.
The study results indicate that mutations in the LTCCs are detected in a high percentage of probands with J-wave syndromes associated with inherited cardiac arrhythmias, suggesting that genetic screening of Ca(v) genes may be a valuable diagnostic tool in identifying individuals at risk. These results are the first to identify CACNA2D1 as a novel BrS susceptibility gene and CACNA1C, CACNB2, and CACNA2D1 as possible novel ERS susceptibility genes.
Adenosine triphosphate (ATP)-sensitive potassium cardiac channels consist of inward-rectifying channel subunits Kir6.1 or Kir6.2 (encoded by KCNJ8 or KCNJ11) and the sulfonylurea receptor subunits ...SUR2A (encoded by ABCC9).
To examine the association of mutations in KCNJ8 with Brugada syndrome (BrS) and early repolarization syndrome (ERS) and to elucidate the mechanism underlying the gain of function of ATP-sensitive potassium channel current.
Direct sequencing of KCNJ8 and other candidate genes was performed on 204 BrS and ERS probands and family members. Whole-cell and inside-out patch-clamp methods were used to study mutated channels expressed in TSA201 cells.
The same missense mutation, p.Ser422Leu (c.1265C>T) in KCNJ8, was identified in 3 BrS and 1 ERS probands but was absent in 430 alleles from ethnically matched healthy controls. Additional genetic variants included CACNB2b-D601E. Whole-cell patch-clamp studies showed a 2-fold gain of function of glibenclamide-sensitive ATP-sensitive potassium channel current when KCNJ8-S422L was coexpressed with SUR2A-wild type. Inside-out patch-clamp evaluation yielded a significantly greater half maximal inhibitory concentration for ATP in the mutant channels (785.5 ± 2 vs 38.4 ± 3 μM; n = 5; P <.01), pointing to incomplete closing of the ATP-sensitive potassium channels under normoxic conditions. Patients with a CACNB2b-D601E polymorphism displayed longer QT/corrected QT intervals, likely owing to their effect to induce an increase in L-type calcium channel current (I(Ca-L)).
Our results support the hypothesis that KCNJ8 is a susceptibility gene for BrS and ERS and point to S422L as a possible hotspot mutation. Our findings suggest that the S422L-induced gain of function in ATP-sensitive potassium channel current is due to reduced sensitivity to intracellular ATP.
Abstract Recent studies have demonstrated an association between mutations in CACNA1c or CACNB2b and Brugada syndrome (BrS). Previously described mutations all caused a loss of function secondary to ...a reduction of peak calcium current ( ICa ). We describe a novel CACNB2b mutation associated with BrS in which loss of function is caused by accelerated inactivation of ICa . The proband, a 32 year old male, displayed a Type I ST segment elevation in two right precordial ECG leads following a procainamide challenge. EP study was positive with induction of polymorphic VT/VF. Interrogation of implanted ICD revealed brief episodes of very rapid ventricular tachycardia. He was also diagnosed with vasovagal syncope. Genomic DNA was isolated from lymphocytes. All exons and intron borders of 15 ion channel genes were amplified and sequenced. The only mutation uncovered was a missense mutation (T11I) in CACNB2b . We expressed WT or T11I CACNB2b in TSA201 cells co-transfected with WT CACNA1c and CACNA2d . Patch clamp analysis showed no significant difference between WT and T11I in peak ICa density, steady-state inactivation or recovery from inactivation. However, both fast and slow decays of ICa were significantly faster in mutant channels between 0 and + 20 mV. Action potential voltage clamp experiments showed that total charge was reduced by almost half compared to WT. We report the first BrS mutation in CaCNB2b resulting in accelerated inactivation of L-type calcium channel current. Our results suggest that the faster current decay results in a loss-of-function responsible for the Brugada phenotype.
Mutations in the
SCN5A
gene, encoding the cardiac voltage-gated sodium channel Na
V
1.5, are associated with inherited cardiac arrhythmia and conduction disease. Ca
2+
-dependent mechanisms and the ...involvement of β-subunit (Na
V
β) in Na
V
1.5 regulation are not fully understood. A patient with severe sinus-bradycardia and cardiac conduction-disease was genetically evaluated and compound heterozygosity in the
SCN5A
gene was found. Mutations were identified in the cytoplasmic DIII-IV linker (K1493del) and the C-terminus (A1924T) of Na
V
1.5, both are putative CaM-binding domains. These mutants were functionally studied in human embryonic kidney (HEK) cells and HL-1 cells using whole-cell patch clamp technique. Calmodulin (CaM) interaction and cell-surface expression of heterologously expressed Na
V
1.5 mutants were studied by pull-down and biotinylation assays. The mutation K1493del rendered Na
V
1.5 non-conductive. Na
V
1.5
K1493del
altered the gating properties of co-expressed functional Na
V
1.5, in a Ca
2+
and Na
V
β1-dependent manner. Na
V
1.5
A1924T
impaired Na
V
β1-dependent gating regulation. Ca
2+
-dependent CaM-interaction with Na
V
1.5 was blunted in Na
V
1.5
K1493del
. Electrical charge substitution at position 1493 did not affect CaM-interaction and channel functionality. Arrhythmia and conduction-disease -associated mutations revealed Ca
2+
-dependent gating regulation of Na
V
1.5 channels. Our results highlight the role of Na
V
1.5 DIII-IV linker in the CaM-binding complex and channel function, and suggest that the Ca
2+
-sensing machinery of Na
V
1.5 involves Na
V
β1.
Background
Phenotypic overlap of type 3 long QT syndrome (LQT3), Brugada syndrome (BrS), cardiac conduction disease (CCD), and sinus node dysfunction (SND) is observed with SCN5A mutations. ...SCN5A‐E1784K is the most common mutation associated with BrS and LQTS3. The present study examines the genotype–phenotype relationship in a large family carrying SCN5A‐E1784K and SCN5A‐H558R polymorphism.
Methods and Results
Clinical work‐up, follow‐up, and genetic analysis were performed in 35 family members. Seventeen were SCN5A‐E1784K positive. They also displayed QTc prolongation, and either BrS, CCD, or both. One carrier exhibited SND. The presence of SCN5A‐H558R did not significantly alter the phenotype of SCN5A‐E1784K carriers. Fourteen SCN5A‐E1784K patients underwent implantable cardioverter‐defibrillator (ICD) implantation; 4 developed VF and received appropriate ICD shocks after 8±3 months of follow‐up. One patient without ICD also developed VF after 6.7 years. These 5 cases carried both SCN5A‐E1784K and SCN5A‐H558R. Functional characterization was achieved by expressing SCN5A variants in TSA201 cells. Peak (INa,P) or late (INa,L) sodium currents were recorded using whole‐cell patch‐clamp techniques. Co‐expression of SCN5A‐E1784K and SCN5A‐WT reduced INa,P to 70.03% of WT, shifted steady‐state inactivation by −11.03 mV, and increased INa,L from 0.14% to 1.86% of INa,P. Similar changes were observed when SCN5A‐E1784K was co‐expressed with SCN5A‐H558R.
Conclusions
We demonstrate a strong genotype‐phenotype correlation with complete penetrance for BrS, LQTS, or CCD in the largest family harboring SCN5A‐E1784K mutation described so far. Phenotype of LQTS is present during all decades of life, whereas CCD develops with increasing age. Phenotypic overlap may explain the high event rate in carriers.
Cardiac sodium channel β-subunit mutations have been associated with several inherited cardiac arrhythmia syndromes.
To identify and characterize variations in SCN1Bb associated with Brugada syndrome ...(BrS) and sudden infant death syndrome (SIDS).
All known exons and intron borders of the BrS-susceptibility genes were amplified and sequenced in both directions. Wild type (WT) and mutant genes were expressed in TSA201 cells and studied using co-immunoprecipitation and whole-cell patch-clamp techniques.
Patient 1 was a 44-year-old man with an ajmaline-induced type 1 ST-segment elevation in V1 and V2 supporting the diagnosis of BrS. Patient 2 was a 62-year-old woman displaying a coved-type BrS electrocardiogram who developed cardiac arrest during fever. Patient 3 was a 4-month-old female SIDS case. A R214Q variant was detected in exon 3A of SCN1Bb (Na(v)1B) in all three probands, but not in any other gene previously associated with BrS or SIDS. R214Q was identified in 4 of 807 ethnically-matched healthy controls (0.50%). Co-expression of SCN5A/WT + SCN1Bb/R214Q resulted in peak sodium channel current (I(Na)) 56.5% smaller compared to SCN5A/WT + SCN1Bb/WT (n = 11-12, P<0.05). Co-expression of KCND3/WT + SCN1Bb/R214Q induced a Kv4.3 current (transient outward potassium current, I(to)) 70.6% greater compared with KCND3/WT + SCN1Bb/WT (n = 10-11, P<0.01). Co-immunoprecipitation indicated structural association between Na(v)β1B and Na(v)1.5 and K(v)4.3.
Our results suggest that R214Q variation in SCN1Bb is a functional polymorphism that may serve as a modifier of the substrate responsible for BrS or SIDS phenotypes via a combined loss of function of sodium channel current and gain of function of transient outward potassium current.
The Brugada syndrome is an arrhythmogenic disease caused in part by mutations in the cardiac sodium channel gene, SCN5A. The electrocardiographic pattern characteristic of the syndrome is dynamic and ...is often absent in affected individuals. Sodium channel blockers are effective in unmasking carriers of the disease. However, the value of the test remains controversial.
We studied 147 individuals representing 4 large families with SCN5A mutations. Of these, 104 were determined to be at possible risk for Brugada syndrome and underwent both electrocardiographic and genetic evaluation. Twenty-four individuals displayed an ECG diagnostic of Brugada syndrome at baseline. Of the remaining, 71 received intravenous ajmaline. Of the 35 genetic carriers who received ajmaline, 28 had a positive test and 7 a negative ajmaline test. The sensitivity, specificity, and positive and negative predictive values of the drug challenge were 80% (28:35), 94.4% (34:36), 93.3% (28:30), and 82.9% (34:41), respectively. Penetrance of the disease phenotype increased from 32.7% to 78.6% with the use of sodium channel blockers. In the absence of ST-segment elevation under baseline conditions, a prolonged P-R interval, but not incomplete right bundle-branch block or early repolarization patterns, indicates a high probability of an SCN5A mutation carrier.
In families with Brugada syndrome, the data suggest that ajmaline testing is valuable in the diagnosis of SCN5A carriers. In the absence of ST-segment elevation at baseline, family members with first-degree atrioventricular block should be suspected of carrying the mutation. An ajmaline test is often the key to making the proper diagnosis in these patients.
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