Stéphanie Chatel

Common variants at SCN5A-SCN10A and HEY2 are associated with Brugada syndrome, a rare disease with high risk of sudden cardiac death

Brugada syndrome is a rare cardiac arrhythmia disorder, causally related to SCN5A mutations in around 20% of cases. Through a genome-wide association study of 312 individuals with Brugada syndrome and 1,115 controls, we detected 2 significant association signals at the SCN10A locus (rs10428132) and near the HEY2 gene (rs9388451). Independent replication confirmed both signals (meta-analyses: rs10428132, P = 1.0 × 10−68; rs9388451, P = 5.1 × 10−17) and identified one additional signal in SCN5A (at 3p21; rs11708996, P = 1.0 × 10−14). The cumulative effect of the three loci on disease susceptibility was unexpectedly large (Ptrend = 6.1 × 10−81). The association signals at SCN5A-SCN10A demonstrate that genetic polymorphisms modulating cardiac conduction can also influence susceptibility to cardiac arrhythmia. The implication of association with HEY2, supported by new evidence that Hey2 regulates cardiac electrical activity, shows that Brugada syndrome may originate from altered transcriptional programming during cardiac development. Altogether, our findings indicate that common genetic variation can have a strong impact on the predisposition to rare diseases.

Molecular Genetics and Functional Anomalies in a Series of 248 Brugada Cases with 11 Mutations in the TRPM4 Channel

Brugada syndrome (BrS) is a condition defined by ST-segment alteration in right precordial leads and a risk of sudden death. Because BrS is often associated with right bundle branch block and the TRPM4 gene is involved in conduction blocks, we screened TRPM4 for anomalies in BrS cases. The DNA of 248 BrS cases with no SCN5A mutations were screened for TRPM4 mutations. Among this cohort, 20 patients had 11 TRPM4 mutations. Two mutations were previously associated with cardiac conduction blocks and 9 were new mutations (5 absent from ∼14′000 control alleles and 4 statistically more prevalent in this BrS cohort than in control alleles). In addition to Brugada, three patients had a bifascicular block and 2 had a complete right bundle branch block. Functional and biochemical studies of 4 selected mutants revealed that these mutations resulted in either a decreased expression (p.Pro779Arg and p.Lys914X) or an increased expression (p.Thr873Ile and p.Leu1075Pro) of TRPM4 channel. TRPM4 mutations account for about 6% of BrS. Consequences of these mutations are diverse on channel electrophysiological and cellular expression. Because of its effect on the resting membrane potential, reduction or increase of TRPM4 channel function may both reduce the availability of sodium channel and thus lead to BrS.

Testing the burden of rare variation in arrhythmia-susceptibility genes provides new insights into molecular diagnosis for Brugada syndrome

The Brugada syndrome (BrS) is a rare heritable cardiac arrhythmia disorder associated with ventricular fibrillation and sudden cardiac death. Mutations in the SCN5A gene have been causally related to BrS in 20-30% of cases. Twenty other genes have been described as involved in BrS, but their overall contribution to disease prevalence is still unclear. This study aims to estimate the burden of rare coding variation in arrhythmia-susceptibility genes among a large group of patients with BrS. We have developed a custom kit to capture and sequence the coding regions of 45 previously reported arrhythmia-susceptibility genes and applied this kit to 167 index cases presenting with a Brugada pattern on the electrocardiogram as well as 167 individuals aged over 65-year old and showing no history of cardiac arrhythmia. By applying burden tests, a significant enrichment in rare coding variation (with a minor allele frequency below 0.1%) was observed only for SCN5A, with rare coding variants carried by 20.4% of cases with BrS versus 2.4% of control individuals (P = 1.4 × 10(-7)). No significant enrichment was observed for any other arrhythmia-susceptibility gene, including SCN10A and CACNA1C. These results indicate that, except for SCN5A, rare coding variation in previously reported arrhythmia-susceptibility genes do not contribute significantly to the occurrence of BrS in a population with European ancestry. Extreme caution should thus be taken when interpreting genetic variation in molecular diagnostic setting, since rare coding variants were observed in a similar extent among cases versus controls, for most previously reported BrS-susceptibility genes.

Identification of Large Families in Early Repolarization Syndrome

OBJECTIVES The aim of this study was to identify families affected by early repolarization syndrome (ERS) and to determine the mode of transmission of the disease. BACKGROUND Early repolarization (ER) has recently been linked to idiopathic ventricular fibrillation. Familial inheritance of the disease has been suggested but not demonstrated. METHODS We screened relatives of 4 families affected by ERS. ER was defined as a distinct J-wave in at least 2 consecutive leads and a 1-mm amplitude above baseline. The Valsalva maneuver was performed in affected and unaffected family members to decrease heart rate and thus increase or reveal an ER pattern. RESULTS Twenty-two sudden cardiac deaths occurred in the 4 families including 10 before 35 years of age. In the 4 families, the prevalence of ER was 56%, 34%, 61%, and 33% of, respectively, 30, 82, 29, and 30 screened relatives. In these families, transmission of an ER pattern is compatible with an autosomal dominant mode of inheritance. All probands were screened for genes identified in ERS, and no mutation was found. The Valsalva maneuver was performed in 80 relatives, resulting in increased J-wave amplitude for 17 of 20 affected patients and revealing an ER pattern in 17 relatives in whom 5 are obligate transmitters of an ER pattern. CONCLUSIONS ERS can be inherited through autosomal dominant transmission and should be considered a real inherited arrhythmia syndrome. Familial investigation can be facilitated by using the Valsalva maneuver to reveal the electrocardiographic pattern in family members. The prognosis value of this test remains to be assessed.

Prevalence and prognostic role of various conduction disturbances in patients with the Brugada syndrome.

Prevalence and prognostic value of conduction disturbances in patients with the Brugada syndrome (BrS) remains poorly known. Electrocardiograms (ECGs) from 325 patients with BrS (47 ± 13 years, 258 men) with spontaneous (n = 143) or drug-induced (n = 182) type 1 ECG were retrospectively reviewed. Two hundred twenty-six patients (70%) were asymptomatic, 73 patients (22%) presented with unexplained syncope, and 26 patients (8%) presented with sudden death or implantable cardioverter-defibrillator appropriated therapies at diagnosis or during a mean follow-up of 48 ± 34 months. P-wave duration of ≥120 ms was present in 129 patients (40%), first degree atrioventricular block (AVB) in 113 (35%), right bundle branch block (BBB) in 90 (28%), and fascicular block in 52 (16%). Increased P-wave duration, first degree AVB, and right BBB were more often present in patients after drug challenge than in patients with spontaneous type 1 ST elevation. Left BBB was present in 3 patients. SCN5A mutation carriers had longer P-wave duration and longer PR and HV intervals. In multivariate analysis, first degree AVB was independently associated with sudden death or implantable cardioverter-defibrillator appropriated therapies (odds ratio 2.41, 95% confidence interval 1.01 to 5.73, p = 0.046) together with the presence of syncope and spontaneous type 1 ST elevation. In conclusion, conduction disturbances are frequent and sometimes diffuse in patients with BrS. First degree AVB is independently linked to outcome and may be proposed to be used for individual risk stratification.

Increased Tpeak-Tend interval is highly and independently related to arrhythmic events in Brugada syndrome

BACKGROUND Risk stratification in Brugada syndrome (BS) remains controversial. The time interval between the peak and the end of the T wave (Tpe interval), a marker of transmural dispersion of repolarization, has been linked to malignant ventricular arrhythmias in various settings but leads to discordant results in BS. OBJECTIVE We study the correlation of the Tpe interval with arrhythmic events in a large cohort of patients with BS. METHODS A total of 325 consecutive patients with BS (mean age 47±13 years, 259 men-80%) with spontaneous (n=143, 44%) or drug-induced (n=182, 56%) type 1 electrocardiogram were retrospectively included. 235 were asymptomatic (70%), 80 presented with unexplained syncope (22%), and 10 presented with sudden death (SD) or appropriate implantable cardioverter-defibrillator therapy (AT) (8%) at diagnosis or over a mean follow-up of 48 ± 34 months. The Tpe interval was calculated as the difference between the QT interval and the QT peak interval as measured in each of the precordial leads. RESULTS The Tpe interval from lead V1 to lead V4, maximum value of the Tpe interval (max Tpe), and Tpe dispersion in all precordial leads were significantly higher in patients with SD/AT or in patients with syncope than in asymptomatic patients (P < .001). A max Tpe of ≥100 ms was present in 47 of 226 asymptomatic patients (21%), in 48 of 73 patients with syncope (66%), and in 22 of 26 patients with SD/AT (85%) (P < .0001). In multivariate analysis, a max Tpe of ≥100 ms was independently related to arrhythmic events (odds ratio 9.61; 95% confidence interval 3.13-29.41; P < .0001). CONCLUSION The Tpe interval in the precordial leads is highly related to malignant ventricular arrhythmias in this large cohort of patients with BS. This simple electrocardiographic parameter could be used to refine risk stratification.

Prevalence, characteristics, and prognosis role of type 1 ST elevation in the peripheral ECG leads in patients with Brugada syndrome

BACKGROUND Despite isolated reports of Brugada syndrome (BrS) in the inferior or lateral leads, the prevalence and prognostic value of ST elevation in the peripheral electrocardiographic (ECG) leads in patients with BrS remain poorly known. OBJECTIVE To study the prevalence, characteristics, and prognostic value of type 1 ST elevation and ST depression in the peripheral ECG leads in a large cohort of patients with BrS. METHODS ECGs from 323 patients with BrS (age 47 ± 13 years; 257 men) with spontaneous (n = 141) or drug-induced (n = 182) type 1 ECG were retrospectively reviewed. Two hundred twenty-five (70%) patients were asymptomatic, 72 (22%) patients presented with unexplained syncope, and 26 (8%) patients presented with sudden death (12 patients) or appropriated implantable cardioverter-defibrillator therapies (14 patients) at diagnosis or over a mean follow-up of 48 ± 34 months. RESULTS Thirty (9%) patients presented with type 1 ST elevation in at least 1 peripheral lead (22 patients in the aVR leads, 2 in the inferior leads, 5 in both aVR and inferior leads, and 1 in the aVR and VL leads). Patients with type 1 ST elevation in the peripheral leads more often had mutations in the SCN5A gene, were more often inducible, had slower heart rate, and higher J-wave amplitude in the right precordial leads. Twenty-seven percent (8 of 30) of the patients with type 1 ST elevation in the peripheral leads experimented sudden death/appropriate implantable cardioverter-defibrillator therapy, whereas it occurred in only 6% (18 of 293) of other patients (P < .0001). In multivariate analysis, type 1 ECG in the peripheral leads was independently associated with malignant arrhythmic events (odds ratio 4.58; 95% confidence interval 1.7-12.32; P = .0025). CONCLUSIONS Type 1 ST elevation in the peripheral ECG leads can be seen in 10% of the patients with BrS and is an independent predictor for a malignant arrhythmic event.

Parental Electrocardiographic Screening Identifies a High Degree of Inheritance for Congenital and Childhood Nonimmune Isolated Atrioventricular Block

Background— The origin of congenital or childhood nonimmune isolated atrioventricular (AV) block remains unknown. We hypothesized that this conduction abnormality in the young may be a heritable disease. Methods and Results— A multicenter retrospective study (13 French referral centers, from 1980–2009) included 141 children with AV block diagnosed in utero, at birth, or before 15 years of age without structural heart abnormalities and without maternal antibodies. Parents and matched control subjects were investigated for family history and for ECG screening. In parents, a family history of sudden death or progressive cardiac conduction defect was found in 1.4% and 11.1%, respectively. Screening ECGs from 130 parents (mean age 42.0±6.8 years, 57 couples) were compared with those of 130 matched healthy control subjects. All parents were asymptomatic and in sinus rhythm, except for 1 with undetected complete AV block. Conduction abnormalities were more frequent in parents than in control subjects, found in 50.8% versus 4.6%, respectively (P<0.001). A long PR interval was found in 18.5% of the parents but never in control subjects (P<0.0001). Complete or incomplete right bundle-branch block was observed in 39.2% of the parents and 1.5% of the control subjects (P<0.0001). Complete or incomplete left bundle-branch block was found in 15.4% of the parents and 3.1% of the control subjects (P<0.0006). Estimated heritability for isolated conduction disturbances was 91% (95% confidence interval, 80%–100%). SCN5A mutation screening identified 2 mutations in 2 patients among 97 children. Conclusions— ECG screening in parents of children affected by idiopathic AV block revealed a high prevalence of conduction abnormalities. These results support the hypothesis of an inheritable trait in congenital and childhood nonimmune isolated AV block.

Biallelic Variants in UBA5 Reveal that Disruption of the UFM1 Cascade Can Result in Early-Onset Encephalopathy

Via whole-exome sequencing, we identified rare autosomal-recessive variants in UBA5 in five children from four unrelated families affected with a similar pattern of severe intellectual deficiency, microcephaly, movement disorders, and/or early-onset intractable epilepsy. UBA5 encodes the E1-activating enzyme of ubiquitin-fold modifier 1 (UFM1), a recently identified ubiquitin-like protein. Biochemical studies of mutant UBA5 proteins and studies in fibroblasts from affected individuals revealed that UBA5 mutations impair the process of ufmylation, resulting in an abnormal endoplasmic reticulum structure. In Caenorhabditis elegans, knockout of uba-5 and of human orthologous genes in the UFM1 cascade alter cholinergic, but not glutamatergic, neurotransmission. In addition, uba5 silencing in zebrafish decreased motility while inducing abnormal movements suggestive of seizures. These clinical, biochemical, and experimental findings support our finding of UBA5 mutations as a pathophysiological cause for early-onset encephalopathies due to abnormal protein ufmylation.

Variants of Transient Receptor Potential Melastatin Member 4 in Childhood Atrioventricular Block

Background Transient receptor potential melastatin member 4 (TRPM4) is a nonselective cation channel. TRPM4 mutations have been linked to cardiac conduction disease and Brugada syndrome. The mechanisms underlying TRPM4‐dependent conduction slowing are not fully understood. The aim of this study was to characterize TRPM4 genetic variants found in patients with congenital or childhood atrioventricular block. Methods and Results Ninety‐one patients with congenital or childhood atrioventricular block were screened for candidate genes. Five rare TRPM4 genetic variants were identified and investigated. The variants were expressed heterologously in HEK293 cells. Two of the variants, A432T and A432T/G582S, showed decreased expression of the protein at the cell membrane; inversely, the G582S variant showed increased expression. Further functional characterization of these variants using whole‐cell patch‐clamp configuration showed a loss of function and a gain of function, respectively. We hypothesized that the observed decrease in expression was caused by a folding and trafficking defect. This was supported by the observation that incubation of these variants at lower temperature partially rescued their expression and function. Previous studies have suggested that altered SUMOylation of TRPM4 may cause a gain of function; however, we did not find any evidence that supports SUMOylation as being directly involved for the gain‐of‐function variant. Conclusions This study underpins the role of TRPM4 in the cardiac conduction system. The loss‐of‐function variants A432T/G582S found in 2 unrelated patients with atrioventricular block are most likely caused by misfolding‐dependent altered trafficking. The ability to rescue this variant with lower temperature may provide a novel use of pharmacological chaperones in treatment strategies.