A study of the SCN5A gene in a cohort of 76 patients with Brugada syndrome

We aim to study the SCN5A gene in a cohort of Brugada syndrome (BS) patients and evaluate the genotype–phenotype correlation. BS is caused by mutations in up to 10 different genes, SCN5A being the most frequently involved. Large genomic rearrangements in SCN5A have been associated with conduction disease, but its prevalence in BS is unknown. Seventy‐six non‐related patients with BS were studied. Clinical characteristics and family risk profile were recorded. Direct sequencing and multiplex ligation‐dependent probe amplification (MLPA) of the SCN5A gene for identification of mutations and larger rearrangements were performed, respectively. Eight patients (10.5%) had point mutations (R27H, E901K, G1743R (detected in three families), V728I, N1443S and E1152X). Patients with mutations had a trend toward a higher proportion of spontaneous type I Brugada electrocardiogram (ECG) (87.5% vs 52.9%, p = 0.06) and had evidence of familial disease (62.5%, vs 23.5%, p = 0.03). The symptoms and risk profile of the carriers were not different from wild‐type probands. There were non‐significant differences in the prevalence of type I ECG, syncope and history of arrhythmia in carriers of selected polymorphisms. None of the patients had any deletion/duplication in the SCN5A gene. In conclusion, 10.5% of our patients had mutations in the SCN5A gene. Patients with mutations seemed to have more spontaneous type I ECG, but no differences in syncope or arrhythmic events compared with patients without mutations. Larger studies are needed to evaluate the role of polymorphisms in the SCN5A in the expression of the phenotype and prognosis. Large rearrangements were not identified in the SCN5A gene using the MLPA technique.     

Sodium channel gene (SCN5A) mutations in 44 index patients with Brugada syndrome: different incidences in familial and sporadic disease

The Brugada syndrome (BS) is a distinct form of idiopathic ventricular fibrillation and may cause sudden cardiac death in healthy young individuals. In the surface ECG, BS can be recognized by an atypical right bundle branch block and ST-segment elevation in the right precordial leads. Mutations in the cardiac sodium channel gene SCN5A are only known to cause BS. In a multi-center effort, we have collected clinical data on 44 unrelated index patients and family members and performed a complete genetic analysis of SCN5A. In 37% the disease was familial, whereas in the majority it was sporadic (63%). Five novel SCN5A mutations (2602delC, resulting in: E867X; 2581_2582del TT: F861fs951X; 2673G>A: E1225K; 4435_4437delAAG: K1479del; and 5425C>A: S1812X) were found and were randomly located in SCN5A. Mutation frequencies (SCN5A+) differed significantly between familial (38%) and sporadic disease (0%) (p=0.001). Disease penetrance was complete in the SCN5A+ adult patients, but incomplete in SCN5A+ children (17%). Genetic testing of SCN5A is especially useful in familial disease to identify individuals at cardiac risk. In sporadic cases, however, a genetic basis and the value of mutation screening has to be further determined. These results are in line with a possibly genetic and clinical heterogeneity of BS.     

Novel mutations in domain I of SCN5A cause Brugada syndrome

Brugada syndrome, an autosomal dominantly inherited form of ventricular fibrillation characterized by ST-segment elevation in leads V1-V3 and right bundle-branch block on surface electrocardiogram, is caused by mutations in the cardiac sodium channel gene SCN5A. Patients with Brugada syndrome were studied using single-strand conformation polymorphism analysis, denaturing high-performance liquid chromatography, and DNA sequencing of SCN5A. Mutations were identified in SCN5A in two families and one sporadic case. In one family, a missense mutation leading to a glycine to valine substitution (G351V) in the pore region between the DIS5 and DIS6 transmembrane segments was detected. Biophysical analysis demonstrated that this mutation caused significant current reduction. In the other family, a 20-bp deletion of the exon 5 splice acceptor site was identified; as exon 5 encodes part of the intracellular loop between DIS2 and DIS3, this portion of the channel is disrupted. In the sporadic patient, a missense mutation resulting in the substitution of lysine by glutamic acid (K126E) in the intracellular loop at the boundary with DIS1 was identified. These three new SCN5A mutations in Brugada syndrome patients are all located within domain I of SCN5A, a region not previously considered important in the development of ventricular arrhythmias.     

Usefulness of patient's history and non-invasive electrocardiographic parameters in prediction of ajmaline test results in patients with suspected Brugada syndrome

Introduction

The aim of the work was to assess the usefulness of patient''s history and non-invasive electrocardiographic parameters in the prediction of ajmaline test results in patients with suspected Brugada syndrome.

Material and methods

The study involved a group of 59 patients (37 men) at average age of 31.6 ±12.2 years with suspected concealed form of Brugada syndrome. Pharmacological provocation with intravenous ajmaline administration was performed. The patients were divided into two groups depending on ajmaline test results. Individual and total predictive value for ajmaline test was based on the analysis of medical anamnesis and non-invasive electrocardiographic examination.

Results

The analysis carried out within the work indicated a special predictive value of 2 parameters which constituted the study inclusion criteria – family history of Brugada syndrome (28.6% vs. 3.8%; p = 0.0477) and occurrence of saddleback electrocardiographic changes in ECG curve (42.9% vs. 0.0%; p = 0.0002). Non-invasive electrocardiographic parameters which showed significant predictive value for ajmaline test were as follows: dispersion of QTc interval (prior to the provocation test 54.43 ±24.77 ms vs. 32.70 ±12.98 ms; p = 0.0005 and during daytime activity 46.81 ±27.16 ms vs. 32.07 ±13.19 ms; p = 0.0198), corrected QT intervals, Tpeak-Tend intervals in particular leads, QTpeak intervals, dispersion of Tpeak-Tend interval assessed from precordial leads (V1–V6) (42.86 ±13.80 ms vs. 26.54 ±11.70 ms; p = 0.001) and J-point elevation in V2 and V3 leads.

Conclusions

Both interview and non-invasive electrocardiographic parameters which reflect cardiomyocyte repolarization disorders are of high predictive value in anticipating ajmaline pharmacological provocation results in patients with suspected Brugada syndrome.     

Genetic and biophysical basis of sudden unexplained nocturnal death syndrome (SUNDS), a disease allelic to Brugada syndrome

Sudden unexplained nocturnal death syndrome (SUNDS), a disorder found in southeast Asia, is characterized by an abnormal electrocardiogram with ST-segment elevation in leads V1-V3 and sudden death due to ventricular fibrillation, identical to that seen in Brugada syndrome. We screened patients with SUNDS for mutations in SCN5A, the gene known to cause Brugada syndrome, as well as genes encoding ion channels associated with the long-QT syndrome. Ten families were enrolled, and screened for mutations using single-strand DNA conformation polymorphism analysis, denaturing high-performance liquid chromatography and DNA sequencing. Mutations were identified in SCN5A in three families. One mutation, R367H, lies in the first P segment of the pore-lining region between the DIS5 and DIS6 transmembrane segments of SCN5A. A second mutation, A735V, lies in the first transmembrane segment of domain II (DIIS1) close to the first extracellular loop between DIIS1 and DIIS2, whereas the third mutation, R1192Q, lies in domain III. Analysis of these mutations in Xenopus oocytes showed that the R367H mutant channel did not express any current and the likely effect of this mutation is to depress peak current due to the loss of one functional allele. The A735V mutant expressed currents with steady state activation voltage shifted to more positive potentials. The R1192Q mutation accelerated the inactivation of the sodium channel current. Both mutations resulted in reduced sodium channel current (I(Na)) at a time corresponding to the end of phase 1 of the action potential, as described previously in the Brugada syndrome. Based upon these observations we suggest that SUNDS and Brugada syndrome are phenotypically, genetically and functionally the same disorder.     

Genetic analysis of the cardiac sodium channel gene SCN5A in Koreans with Brugada syndrome

The SCN5A gene encodes the alpha subunit of the human cardiac voltage-gated sodium channel. Mutations in SCN5A are responsible for Brugada syndrome, an inherited cardiac disease that leads to idiopathic ventricular fibrillation (IVF) and sudden death. In this study, we screened nine individuals from a single family and 12 sporadic patients who were clinically diagnosed with Brugada syndrome. Using PCR-SSCP, DHPLC, and DNA sequencing analysis, we identified a novel single missense mutation associated with Brugada syndrome in the family and detected a C5607T polymorphism in Korean subjects. A single nucleotide substitution of G to A at nucleotide position 3934 changed the coding sense of exon 21 of the SCN5A from glycine to serine (G1262S) in segment 2 of domain III (DIII-S2). Four individuals in the family carried the identical mutation in the SCN5A gene, but none of the 12 sporadic patients did. This mutation was not found in 150 unrelated normal individuals. This finding is the first report of a novel mutation in SCN5A associated with Brugada syndrome in Koreans.     

Identifying patterns of spatial current dispersion that characterise and separate the brugada syndrome and complete right-bundle branch block

The aim of the study was to detect patterns of spatial-current distribution in the late QRS and early ST-segments that distinguish Brugada-syndrome cases from complete right-bundle branch block (CRBBB). Magnetocardiograms (MCGs) were recorded from Brugada-syndrome patients (n=6), CRBBB patients (n=4) and the members of a control group (n=33). The current distributions at six time points from Q-onset were estimated by producing current-arrow maps (CAMs). The angle of the current arrow of maximum amplitude at each time point was calculated. In the Brugada cases, the characteristic ST elevation was seen above the upper right chest, and abnormal currents appeared to be present in the right-ventricular outflow tract (RVOT). The angles of the abnormal arrows were −78°±51° at 100ms and −50°±61° at 110ms. In the cases of CRBBB, wide S- and R-waves were recorded above the upper right and lower right chest, respectively. The angles of the abnormal arrows for CRBBB were 152°±19° at 100ms, 159°±20° at 110ms, and 157°±19° at 120ms. The findings suggest that an abnormal current from the RVOT to the upper left chest may be a feature of the Brugada syndrome, and that the direction of this current is completely different from that seen in CRBBB.     

Brugada syndrome: clinical and genetic findings

Brugada syndrome is a rare, inherited cardiac disease leading to ventricular fibrillation and sudden cardiac death in structurally normal hearts. Clinical diagnosis requires a Brugada type I electrocardiographic pattern in combination with other clinical features. The most effective approach to unmasking this diagnostic pattern is the use of ajmaline and flecainide tests, and the most effective intervention to reducing the risk of death is the implantation of a cardioverter defibrillator. To date, 18 genes have been associated with the disease, with the voltage-gated sodium channel α type V gene (SCN5A) being the most common one to date. However, only 30–35% of diagnosed cases are attributable to pathogenic variants in known genes, emphasizing the need for further genetic studies. Despite recent advances in clinical diagnoses and genetic testing, risk stratification and clinical management of patients with Brugada syndrome remain challenging.     

TRPM4 mutations to cause autosomal recessive and not autosomal dominant Brugada type 1 syndrome

Cardiac channelopathies, mainly Long QT and Brugada syndromes, are genetic disorders for which genotype/phenotypes relationships remains to be improved. To provide new insights into the Brugada syndrome pathophysiology, a mutational study was performed on a 64-year-old man presented with isolated exertional dyspnea (NYHA class: II-III), hypertension, chronic kidney disease, coronary disease, an electrocardiogram suggesting a Brugada type 1-like pattern with ST-segment elevation in leads V1-V2. Molecular diagnosis study was performed using molecular strategy based on the sequencing of a panel of 19 Brugada-associated genes. The proband was carrier of 2 TRPM4 null alleles [IVS9+1G > A and p. Trp525X] resulting in the absence of functional hTRPM4 proteins. Due to this unexpected genotype, meta-analysis of previously reported TRPM4 variations associated with cardiac pathologies was performed using ACMG guidelines. All were detected in a heterozygous status. This additional meta-analysis indicated that most of them could not be considered definitely as pathogen. In conclusion, our study reports, for the first time, identification of compound heterozygous TRPM4 null mutations in a proband with, at an arrhythmogenic level, only a Brugada type 1-like electrocardiogram. By combining the genotype/phenotype relationship of this case and analysis of previously reported TRPM4 variations, we suggest that loss-of-function TRPM4 variations, in a heterozygous status, could not be considered as pathogenic or likely pathogenic mutations in cardiac channelopathies such as Long QT syndrome or Brugada syndrome.     

SCN4A variants and Brugada syndrome: phenotypic and genotypic overlap between cardiac and skeletal muscle sodium channelopathies

SCN5A mutations involving the α-subunit of the cardiac voltage-gated muscle sodium channel (NaV1.5) result in different cardiac channelopathies with an autosomal-dominant inheritance such as Brugada syndrome. On the other hand, mutations in SCN4A encoding the α-subunit of the skeletal voltage-gated sodium channel (NaV1.4) cause non-dystrophic myotonia and/or periodic paralysis. In this study, we investigated whether cardiac arrhythmias or channelopathies such as Brugada syndrome can be part of the clinical phenotype associated with SCN4A variants and whether patients with Brugada syndrome present with non-dystrophic myotonia or periodic paralysis and related gene mutations. We therefore screened seven families with different SCN4A variants and non-dystrophic myotonia phenotypes for Brugada syndrome and performed a neurological, neurophysiological and genetic work-up in 107 Brugada families. In the families with an SCN4A-associated non-dystrophic myotonia, three patients had a clinical diagnosis of Brugada syndrome, whereas we found a remarkably high prevalence of myotonic features involving different genes in the families with Brugada syndrome. One Brugada family carried an SCN4A variant that is predicted to probably affect function, one family suffered from a not genetically confirmed non-dystrophic myotonia, one family was diagnosed with myotonic dystrophy (DMPK gene) and one family had a Thomsen disease myotonia congenita (CLCN1 variant that affects function). Our findings and data suggest a possible involvement of SCN4A variants in the pathophysiological mechanism underlying the development of a spontaneous or drug-induced type 1 electrocardiographic pattern and the occurrence of malignant arrhythmias in some patients with Brugada syndrome.     

Brugada综合征亚型相关致病基因的研究进展

Brugada综合征是常染色体显性遗传病,全球发病率约万分之五.目前发现9种致病基因与该病存在关联.在发现的约100个基因突变位点中,96个基因突变位于SCN5A基因,这些突变可以解释20%-25%的BrS病因.本综述依据目前研究进展分别将Brugada综合征9种亚型致病基因介绍如下.     

Non-SCN5A Related Brugada Syndromes: Verification of Normal Splicing and Trafficking of SCN5A Without Exonic Mutations

Recently, it has been reported that under 20% of Brugada syndrome cases are linked to SCN5A mutations. The purpose of this study was to clarify whether abnormalities other than exonic mutations, such as splicing disorders, decreased mRNA expression levels, or membrane transport abnormalities of SCN5A, play a role in the pathogenesis of Brugada syndrome.
We analyzed all SCN5A exons and splice sites using genomic DNA from 23 Brugada syndrome patients. We also analyzed the mRNA obtained from RV cardiomyocytes using real time PCR and sequencing, to study the expression levels and splicing patterns of SCN5A . The localization of SCN5A was examined by immunofluorescence analysis.
A de novo heterozygous G to A transversion in a 5' splice junction of the intron between exons 21 and 22 was detected in 1 patient. In the mRNA analysis of Brugada syndrome patients without a mutation of SCN5A no splicing abnormalities were detected, and the SCN5A mRNA levels were similar to those of normal controls. Immunofluorescence analyses revealed that SCN5A is located on the surface membrane not only in the RV cardiomyocytes of normal controls but also in those with Brugada syndrome.
We can confirm that some Brugada syndrome patients without exonic mutations in SCN5A had no other SCN5A abnormalities, including any involving the location of the SCN5A protein. These results suggest the involvement of other proteins in the pathogenesis in Brugada syndrome.     

Genetics can contribute to the prognosis of Brugada syndrome: a pilot model for risk stratification

Brugada syndrome is an inherited arrhythmogenic disorder leading to sudden death predominantly in the 3–4 decade. To date the only reliable treatment is the implantation of a cardioverter defibrillator; however, better criteria for risk stratification are needed, especially for asymptomatic subjects. Brugada syndrome genetic bases have been only partially understood, accounting for <30% of patients, and have been poorly correlated with prognosis, preventing inclusion of genetic data in current guidelines. We designed an observational study to identify genetic markers for risk stratification of Brugada patients by exploratory statistical analysis. The presence of genetic variants, identified by SCN5A gene analysis and genotyping of 73 candidate polymorphisms, was correlated with the occurrence of major arrhythmic events in a cohort of 92 Brugada patients by allelic association and survival analysis. In all, 18 mutations were identified in the SCN5A gene, including 5 novel, and statistical analysis indicated that mutation carriers had a significantly increased risk of major arrhythmic events (P=0.024). In addition, we established association of five polymorphisms with major arrhythmic events occurrence and consequently elaborated a pilot risk stratification algorithm by calculating a weighted genetic risk score, including the associated polymorphisms and the presence of SCN5A mutation as function of their odds ratio. This study correlates for the first time the presence of genetic variants with increased arrhythmic risk in Brugada patients, representing a first step towards the design of a new risk stratification model.     

The genetic basis of Brugada syndrome: A mutation update

Brugada syndrome (BrS) is a condition characterized by a distinct ST‐segment elevation in the right precordial leads of the electrocardiogram and, clinically, by an increased risk of cardiac arrhythmia and sudden death. The condition predominantly exhibits an autosomal dominant pattern of inheritance with an average prevalence of 5:10,000 worldwide. Currently, more than 100 mutations in seven genes have been associated with BrS. Loss‐of‐function mutations in SCN5A, which encodes the α‐subunit of the Na_v1.5 sodium ion channel conducting the depolarizing I_Na current, causes 15–20% of BrS cases. A few mutations have been described in GPD1L, which encodes glycerol‐3‐phosphate dehydrogenase‐1 like protein; CACNA1C, which encodes the α‐subunit of the Ca_v1.2 ion channel conducting the depolarizing I_L,Ca current; CACNB2, which encodes the stimulating β2‐subunit of the Ca_v1.2 ion channel; SCN1B and SCN3B, which, in the heart, encodes β‐subunits of the Na_v1.5 sodium ion channel, and KCNE3, which encodes the ancillary inhibitory β‐subunit of several potassium channels including the Kv4.3 ion channel conducting the repolarizing potassium I_to current. BrS exhibits variable expressivity, reduced penetrance, and “mixed phenotypes,” where families contain members with BrS as well as long QT syndrome, atrial fibrillation, short QT syndrome, conduction disease, or structural heart disease, have also been described. Hum Mutat 30:1–11, 2009. © 2009 Wiley‐Liss, Inc.     

FGFR2 mutation associated with clinical manifestations consistent with Antley-Bixler syndrome

The Antley-Bixler syndrome (ABS) is a rare syndrome with synostosis of cranial sutures and elbow joints as minimal diagnostic criteria. The inheritance has been suggested to be autosomal recessive based on two families with sib recurrence with both sexes being affected, and two cases born to consanguineous parents. We report the first case of ABS associated with an apparent dominant de novo mutation in the fibroblast growth factor receptor 2 (FGFR2) gene. The patient was found to be heterozygous for a C→G transversion at nucleotide 1064, which predicts a Ser351Cys amino acid substitution in the IgIII domain of FGFR2. Apart from the craniosynostosis and elbow ankylosis, our patient also presented with severe spinal dysraphism, the first report of such a finding in association with ABS. This suggests that FGFR2 is expressed as early as the fourth week of embryogenesis when somite formation occurs. We propose that the Antley-Bixler syndrome is an autosomal dominant condition with possible gonadal mosaicism. Alternatively, there may be two types of ABS: an autosomal dominant form and an autosomal recessive form. In light of our findings, FGFR mutations should be looked for in other craniosynostosis patients with elbow synostosis. Am. J. Med. Genet. 77:219–224, 1998. © 1998 Wiley-Liss, Inc.     

Chromosomal aberrations in Bloom syndrome patients with myeloid malignancies.

Bloom syndrome (BS) predisposes affected individuals to a wide variety of neoplasms including hematological malignancies. Thus far, cytogenetic findings in hematological neoplasms have been reported in only a few BS patients. We present the karyotypic findings in a BS patient diagnosed with acute myeloid leukemia (AML), FAB subtype M1, and a review of the literature, showing the preferential occurrence of total or partial loss of chromosome 7 in BS patients with AML or myelodysplastic syndromes (MDS).     

EMBASE search strategies for identifying methodologically sound diagnostic studies for use by clinicians and researchers

Background

The recurrence of cardiac events in patients with idiopathic ventricular fibrillation (VF) excluding patients with the Brugada syndrome is unclear since this entity remains present in previous studies.

Methods

Since 1992, 18 patients (72% male) with idiopathic VF out of 455 ICD implants were treated with an implantable cardioverter defibrillator (ICD). The mean age at first ICD implantation was 42 ± 14 years. Brugada syndrome, as well as other primary electrical diseases (e.g. long QT), were systematically excluded in all patients by the absence of the typical electrocardiogram (ST elevation in the right precordial leads) at rest and/or after pharmacological tests (ajmaline, flecainide, or procainamide). Recurrence of cardiac events was prospectively assessed.

Results

During a mean follow-up period of 41 ± 27 months, VF recurrence with appropriate shock occurred in 7 patients (39%) covering a total of 27 shocks. The median time to first appropriate shock was 12 ± 9 months. There were no deaths. In the electrophysiological study, 39% of patients were inducible, but inducibility failed to predict subsequent arrhythmic events. Forty-four percent of patients suffered 21 inappropriate shocks, which were caused by sinus tachycardia, atrial arrhythmias or lead malfunction.

Conclusion

Idiopathic ventricular fibrillation patients have a high recurrence rate of potentially fatal ventricular arrhythmias, excluding patients with the Brugada syndrome or other known causes. ICD prevents sudden cardiac death but inappropriate shocks remained a major issue in this young and active population.     

ST changes in relation to heart rate during bicycle exercise in patients with coronary artery disease

Exercise test on cycle ergometer and coronary angiography were performed on 190 patients with chest pain. Volunteers with a normal thallium scintigraphy (n = 47) served as controls. The load started at 20 W and increased at a rate of 10 W min-1 until exhaustion or symptoms. Conventional 12-lead ECGs were recorded by means of computer before, during and after exercise. Minimum ST amplitude 60 ms after the STJ point (ST60) at end of work with a cut-off level of -1.10 mm had a sensitivity of 69% (52/75) and a specificity of 89% (37/42) when individuals with a normal resting ECG were considered. ST80 and sum of ST60 in left ventricular leads had slightly lower values of sensitivity and specificity. Changes in ST60 during exercise discriminated less well between the groups. Final heart rate during exercise (less than 148 min-1) had a sensitivity of 88% (53/60) and a specificity of 89% (42/47). The change in heart rate during exercise (less than 66 min-1) had a sensitivity of 50/60 (only patients without beta-blockers were considered). The best discrimination was obtained by defining a test score (TS) according to the linear equation TS = 2.95-0.23 x HRE-0.301 X ST60 where a positive value indicates a positive test and a negative value a negative test. Sensitivity and specificity were 21/23 (91%) and 40/42 (95%), respectively. The test score was also calculated in those patients having significant coronary disease and an abnormal resting ECG (no bundle branch block, no beta-blockers) and this yielded a sensitivity of 30/34.     

Detection of HSV-1 DNA in patients with Beh?et's syndrome and in patients with recurrent oral ulcers by the polymerase chain reaction

The polymerase chain reaction was used to detect HSV-1 DNA in genomic DNA extracted from peripheral blood leucocytes, in patients with Beh?et's syndrome (BS), patients with recurrent oral ulcers and normal healthy controls. A 211-bp HSV-1 DNA fragment was found in a significant number of patients with BS (p less than 0.02). Serum anti-HSV-1 antibodies were also found in a higher proportion of patients with BS (p less than 0.02) than in healthy controls. However, virus-specific DNA was not detected in biopsy samples taken from oral ulcers in patients with BS.