Progressive Atrial Conduction Defects Associated With Bone Malformation Caused by a Connexin-45 Mutation.

BACKGROUND: Inherited cardiac conduction disease is a rare bradyarrhythmia associated with mutations in various genes that affect action potential propagation. It is often characterized by isolated conduction disturbance of the His-Purkinje system, but it is rarely described as a syndromic form. OBJECTIVES: The authors sought to identify the genetic defect in families with a novel bradyarrhythmia syndrome associated with bone malformation. METHODS: The authors genetically screened 15 European cases with genotype-negative de novo atrioventricular (AV) block and their parents by trio whole-exome sequencing, plus 31 Japanese cases with genotype-negative familial AV block or sick sinus syndrome by targeted exon sequencing of 457 susceptibility genes. Functional consequences of the mutation were evaluated using an in vitro cell expression system and in vivo knockout mice. RESULTS: The authors identified a connexin-45 (Cx45) mutation (p.R75H) in 2 unrelated families (a de novo French case and a 3-generation Japanese family) who presented with progressive AV block, which resulted in atrial standstill without ventricular conduction abnormalities. Affected individuals shared a common extracardiac phenotype: a brachyfacial pattern, finger deformity, and dental dysplasia. Mutant Cx45 expressed in Neuro-2a cells showed normal hemichannel assembly and plaque formation. However, Lucifer yellow dye transfer and gap junction conductance between cell pairs were severely impaired, which suggested that mutant Cx45 impedes gap junction communication in a dominant-negative manner. Tamoxifen-induced, cardiac-specific Cx45 knockout mice showed sinus node dysfunction and atrial arrhythmia, recapitulating the intra-atrial disturbance. CONCLUSIONS: Altogether, the authors showed that Cx45 mutant p.R75H is responsible for a novel disease entity of progressive atrial conduction system defects associated with craniofacial and dentodigital malformation.

The QUIDAM study: Hydroquinidine therapy for the management of Brugada syndrome patients at high arrhythmic risk.

BACKGROUND: Although the implantable cardioverter-defibrillator (ICD) remains the main therapy for Brugada syndrome (BrS), it does not reduce life-threatening ventricular arrhythmia. Based on pathophysiologic mechanisms, hydroquinidine (HQ) has been suggested for effective prevention of arrhythmia. OBJECTIVE: The purpose of this study was to provide evidence-based data supporting HQ use to prevent life-threatening ventricular arrhythmia in high-risk patients with BrS. METHODS: We performed a prospective multicenter randomized (HQ vs placebo) double-blind study with two 18-month crossover phases in patients with BrS and implanted with an ICD. RESULTS: Among the 50 patients enrolled (mean age 47.0 ± 11.4 years, 42 [84%] male), 26 (52%) fully completed both phases. Thirty-four (68%) presented HQ-related side effects, mainly gastrointestinal, which led to discontinuation of the therapy in 13 (26%). HQ lengthened the QTc interval (409 ± 32 ms vs 433 ± 37 ms; P = .027) and increased repolarization dispersion as evaluated by Tpe max in precordial leads (89 ± 15 ms vs 108 ± 27 ms; P <.0001) with no significant changes in J-point elevation. During the 36-month follow-up, 1 appropriate ICD shock (0.97% event per year), 1 self-terminating ventricular fibrillation, and 1 inappropriate ICD shock occurred under placebo therapy. No arrhythmic events were reported under HQ therapy. CONCLUSION: Although HQ seems to be effective in preventing life-threatening ventricular arrhythmia, it could not be an alternative for ICD implantation. Its frequent side effects greatly reduce its probable compliance and therefore do not reveal a significant effect. HQ increases repolarization dispersal with no changes in BrS pattern, which could indicate a more complex action of HQ than its Ito blocking effect alone.

Targeted resequencing identifies TRPM4 as a major gene predisposing to progressive familial heart block type I.

BACKGROUND: Progressive cardiac conduction disease (PCCD) is one of the most common cardiac conduction disturbances. It has been causally related to rare mutations in several genes including SCN5A, SCN1B, TRPM4, LMNA and GJA5. METHODS AND RESULTS: In this study, by applying targeted next-generation sequencing (NGS) in 95 unrelated patients with PCCD, we have identified 13 rare variants in the TRPM4 gene, two of which are currently absent from public databases. This gene encodes a cardiac calcium-activated cationic channel which precise role and importance in cardiac conduction and disease is still debated. One novel variant, TRPM4-p.I376T, is carried by the proband of a large French 4-generation pedigree. Systematic familial screening showed that a total of 13 family members carry the mutation, including 10 out of the 11 tested affected individuals versus only 1 out of the 21 unaffected ones. Functional and biochemical analyses were performed using HEK293 cells, in whole-cell patch-clamp configuration and Western blotting. TRPM4-p.I376T results in an increased current density concomitant to an augmented TRPM4 channel expression at the cell surface. CONCLUSIONS: This study is the first extensive NGS-based screening of TRPM4 coding variants in patients with PCCD. It reports the third largest pedigree diagnosed with isolated Progressive Familial Heart Block type I and confirms that this subtype of PCCD is caused by mutation-induced gain-of-expression and function of the TRPM4 ion channel.

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.

Identification of a strong genetic background for progressive cardiac conduction defect by epidemiological approach.

INTRODUCTION: Progressive cardiac conduction defect (PCCD) is a frequent disease attributed to degeneration and fibrosis of the His bundle. Over the past years, gene defects have been identified demonstrating that PCCD could be a genetic disease. The aim of this study was to show a familial aggregation for PCCD using a genetic epidemiological approach to improve in fine genetic knowledge of the transmission of the disease. METHODS AND RESULTS: Using the French social security number, the authors have been able to determine the city of birth of the 6667 patients implanted with a pacemaker (PM) for PCCD between 1995 and 2005 in the western part of France. The authors then mapped the frequency of PM implantations for PCCD. A large heterogeneity of the frequency of the disease has been observed, with a frequency of 0.21% in the major city (Nantes) ranging up to 2.28% in specific parishes. Familial studies performed in the parishes with the highest frequency of the disease allowed the authors to identify five large families with PCCD. Clinical investigations demonstrated phenotype heterogeneity between families. Three patterns have been differentiated. CONCLUSIONS: This study demonstrates a disparate geographical repartition of the frequency of PM implantation in the area of the authors at least in part related to a hereditary factor. The identification of five large families affected by PCCD using epidemiological approach underlines the existence of a major genetic background in PCCD.

Characteristics and long-term outcome of non-immune isolated atrioventricular block diagnosed in utero or early childhood: a multicentre study.

AIMS: The natural history of congenital or childhood non-immune, isolated atrioventricular (AV) block is poorly defined. METHODS AND RESULTS: We retrospectively studied 141 children with isolated, non-immune AV block diagnosed in utero, or up to 15 years of age, at 13 French medical centres, between 1980 and 2009. Patients with structural heart disease or maternal antibodies were excluded. Atrioventricular block was asymptomatic in 119 (84.4%) and complete in 100 (70.9%) patients. There was progression to complete AV block in 29/41 (70.7%) patients with incomplete AV block over 2.8 ± 3.4 years (1-155 months), but all patients with incomplete AV block may not have been included in the study. Narrow QRS complex was present in 18 of 26 patients (69.2%) with congenital, and 106 of 115 (92.2%) with childhood AV block. Pacemakers were implanted in 112 children (79.4%), during the first year of life in 18 (16.1%) and before 10 years of age in 90 (80.4%). The mean interval between diagnosis of AV block and pacemaker implants was 2.6 ± 3.9 years (0-300 months). The pacing indication was prophylactic in 70 children (62.5%). During a mean follow-up of 11.6 ± 6.7 years (1-32 years), no patient died or developed dilated cardiomyopathy (DCM). The long-term follow-up was uncomplicated in 127 children (90.1%). CONCLUSION: In this large multicentre study, the long-term outcome of congenital or childhood non-immune, isolated AV block was favourable, regardless of the patient's age at the time of diagnosis. No patient died or developed DCM, and pacemaker-related complications were few.

Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii: Part I. Model development and parameter identification.

Chlamydomonas reinhardtii is a green microalga capable of turning its metabolism towards H2 production under specific conditions. However this H2 production, narrowly linked to the photosynthetic process, results from complex metabolic reactions highly dependent on the environmental conditions of the cells. A kinetic model has been developed to relate culture evolution from standard photosynthetic growth to H2 producing cells. It represents transition in sulfur-deprived conditions, known to lead to H2 production in Chlamydomonas reinhardtii, and the two main processes then induced which are an over-accumulation of intracellular starch and a progressive reduction of PSII activity for anoxia achievement. Because these phenomena are directly linked to the photosynthetic growth, two kinetic models were associated, the first (one) introducing light dependency (Haldane type model associated to a radiative light transfer model), the second (one) making growth a function of available sulfur amount under extracellular and intracellular forms (Droop formulation). The model parameters identification was realized from experimental data obtained with especially designed experiments and a sensitivity analysis of the model to its parameters was also conducted. Model behavior was finally studied showing interdependency between light transfer conditions, photosynthetic growth, sulfate uptake, photosynthetic activity and O2 release, during transition from oxygenic growth to anoxic H2 production conditions.

Hydrogen production by Chlamydomonas reinhardtii: an elaborate interplay of electron sources and sinks.

The unicellular green alga Chlamydomonas reinhardtii possesses a [FeFe]-hydrogenase HydA1 (EC 1.12.7.2), which is coupled to the photosynthetic electron transport chain. Large amounts of H2 are produced in a light-dependent reaction for several days when C. reinhardtii cells are deprived of sulfur. Under these conditions, the cells drastically change their physiology from aerobic photosynthetic growth to an anaerobic resting state. The understanding of the underlying physiological processes is not only important for getting further insights into the adaptability of photosynthesis, but will help to optimize the biotechnological application of algae as H2 producers. Two of the still most disputed questions regarding H2 generation by C. reinhardtii concern the electron source for H2 evolution and the competition of the hydrogenase with alternative electron sinks. We analyzed the H2 metabolism of S-depleted C. reinhardtii cultures utilizing a special mass spectrometer setup and investigated the influence of photosystem II (PSII)- or ribulosebisphosphate-carboxylase/oxygenase (Rubisco)-deficiency. We show that electrons for H2-production are provided both by PSII activity and by a non-photochemical plastoquinone reduction pathway, which is dependent on previous PSII activity. In a Rubisco-deficient strain, which produces H2 also in the presence of sulfur, H2 generation seems to be the only significant electron sink for PSII activity and rescues this strain at least partially from a light-sensitive phenotype. The latter indicates that the down-regulation of assimilatory pathways in S-deprived C. reinhardtii cells is one of the important prerequisites for a sustained H2 evolution.

Autotrophic and mixotrophic hydrogen photoproduction in sulfur-deprived chlamydomonas cells.

In Chlamydomonas reinhardtii cells, H2 photoproduction can be induced in conditions of sulfur deprivation in the presence of acetate. The decrease in photosystem II (PSII) activity induced by sulfur deprivation leads to anoxia, respiration becoming higher than photosynthesis, thereby allowing H2 production. Two different electron transfer pathways, one PSII dependent and the other PSII independent, have been proposed to account for H2 photoproduction. In this study, we investigated the contribution of both pathways as well as the acetate requirement for H2 production in conditions of sulfur deficiency. By using 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), a PSII inhibitor, which was added at different times after the beginning of sulfur deprivation, we show that PSII-independent H2 photoproduction depends on previously accumulated starch resulting from previous photosynthetic activity. Starch accumulation was observed in response to sulfur deprivation in mixotrophic conditions (presence of acetate) but also in photoautotrophic conditions. However, no H2 production was measured in photoautotrophy if PSII was not inhibited by DCMU, due to the fact that anoxia was not reached. When DCMU was added at optimal starch accumulation, significant H2 production was measured. H2 production was enhanced in autotrophic conditions by removing O2 using N2 bubbling, thereby showing that substantial H2 production can be achieved in the absence of acetate by using the PSII-independent pathway. Based on these data, we discuss the possibilities of designing autotrophic protocols for algal H2 photoproduction.