Hervé Le Marec

Absence of triadin, a protein of the calcium release complex, is responsible for cardiac arrhythmia with sudden death in human

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease so far related to mutations in the cardiac ryanodine receptor (RYR2) or the cardiac calsequestrin (CASQ2) genes. Because mutations in RYR2 or in CASQ2 are not retrieved in all CPVT cases, we searched for mutations in the physiological protein partners of RyR2 and CSQ2 in a large cohort of CPVT patients with no detected mutation in these two genes. Based on a candidate gene approach, we focused our investigations on triadin and junctin, two proteins that link RyR2 and CSQ2. Mutations in the triadin (TRDN) and in the junctin (ASPH) genes were searched in a cohort of 97 CPVT patients. We identified three mutations in triadin which cosegregated with the disease on a recessive mode of transmission in two families, but no mutation was found in junctin. Two TRDN mutations, a 4 bp deletion and a nonsense mutation, resulted in premature stop codons; the third mutation, a p.T59R missense mutation, was further studied. Expression of the p.T59R mutant in COS-7 cells resulted in intracellular retention and degradation of the mutant protein. This was confirmed after in vivo expression of the mutant triadin in triadin knock-out mice by viral transduction. In this work, we identified TRDN as a new gene responsible for an autosomal recessive form of CPVT. The mutations identified in the two families lead to the absence of the protein, thereby demonstrating the importance of triadin for the normal function of the cardiac calcium release complex in humans.

Beta 3‐adrenoceptor stimulation induces vasorelaxation mediated essentially by endothelium‐derived nitric oxide in rat thoracic aorta

The relaxant effects of isoprenaline may result from activation of another β‐adrenoceptor subtype in addition to β1 and β2. This study evaluated the role of a third β‐adrenoceptor subtype, β3, in β‐adrenoceptor‐induced relaxation of rat thoracic aorta by isoprenaline. Isoprenaline produced a concentration‐dependent relaxation of phenylephrine pre‐contracted rings of the thoracic aorta (pD2=7.46±0.15; Emax=85.9±3.4%), which was partially attenuated by endothelium removal (Emax=66.5±6.3%) and administration of the nitric oxide (NO) synthase inhibitor, L‐NG‐monomethyl arginine (L‐NMMA) (Emax=61.3±7.9%). In the presence of nadolol, a β1‐ and β2‐adrenoceptor antagonist, isoprenaline‐induced relaxation persisted (Emax=55.6±5.3%), but occurred at higher concentrations (pD2=6.71±0.10) than in the absence of nadolol and lasted longer. Similar relaxant effects were obtained with two β3‐adrenoceptor agonists: SR 58611 (a preferential β3‐adrenoceptor agonist), and CGP 12177 (a partial β3‐adrenoceptor with β1‐ and β2‐adrenoceptor antagonistic properties). SR 58611 caused concentration‐dependent relaxation (pD2=5.24±0.07; Emax=59.5±3.7%), which was not modified by pre‐treatment with nadolol but antagonized by SR 59230A, a β3‐adrenoceptor antagonist. The relaxation induced by SR 58611 was associated with a 1.7 fold increase in tissue cyclic GMP content. Both relaxation and the cyclic GMP increase induced by SR 58611 were greatly reduced by endothelium removal and in the presence of L‐NMMA. We conclude that in the rat thoracic aorta, β3‐adrenoceptors are mainly located on endothelial cells, and act in conjuction with β1‐ and β2‐adrenoceptors to mediate relaxation through activation of an NO synthase pathway and subsequent increase in cyclic GMP levels.

Dysfunction in ankyrin-B-dependent ion channel and transporter targeting causes human sinus node disease.

The identification of nearly a dozen ion channel genes involved in the genesis of human atrial and ventricular arrhythmias has been critical for the diagnosis and treatment of fatal cardiovascular diseases. In contrast, very little is known about the genetic and molecular mechanisms underlying human sinus node dysfunction (SND). Here, we report a genetic and molecular mechanism for human SND. We mapped two families with highly penetrant and severe SND to the human ANK2 (ankyrin-B/AnkB) locus. Mice heterozygous for AnkB phenocopy human SND displayed severe bradycardia and rate variability. AnkB is essential for normal membrane organization of sinoatrial node cell channels and transporters, and AnkB is required for physiological cardiac pacing. Finally, dysfunction in AnkB-based trafficking pathways causes abnormal sinoatrial node (SAN) electrical activity and SND. Together, our findings associate abnormal channel targeting with human SND and highlight the critical role of local membrane organization for sinoatrial node excitability.

Progressive Cardiac Conduction Defect is the Prevailing Phenotype in Carriers of a Brugada Syndrome SCN5A Mutation

Introduction: Loss‐of‐function mutations in the SCN5A gene encoding the cardiac sodium channel are responsible for Brugada syndrome (BS) and also for progressive cardiac conduction disease (inherited Lenègre disease). In an attempt to clarify the frontier between these two entities, we have characterized cardiac conduction defect and its evolution with aging in a cohort of 78 patients carrying a SCN5A mutation linked to Brugada syndrome.

Identification of Large Families in Early Repolarization Syndrome

OBJECTIVESnThe aim of this study was to identify families affected by early repolarization syndrome (ERS) and to determine the mode of transmission of the disease.nnnBACKGROUNDnEarly repolarization (ER) has recently been linked to idiopathic ventricular fibrillation. Familial inheritance of the disease has been suggested but not demonstrated.nnnMETHODSnWe 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.nnnRESULTSnTwenty-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.nnnCONCLUSIONSnERS 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.

Na+ channel mutation leading to loss of function and non-progressive cardiac conduction defects

BACKGROUNDnWe previously described a Dutch family in which congenital cardiac conduction disorder has clinically been identified. The ECG of the index patient showed a first-degree AV block associated with extensive ventricular conduction delay. Sequencing of the SCN5A locus coding for the human cardiac Na+ channel revealed a single nucleotide deletion at position 5280, resulting in a frame-shift in the sequence coding for the pore region of domain IV and a premature stop codon at the C-terminus.nnnMETHODS AND RESULTSnWild type and mutant Na+ channel proteins were expressed in Xenopus laevis oocytes and in mammalian cells. Voltage clamp experiments demonstrated the presence of fast activating and inactivating inward currents in cells expressing the wild type channel alone or in combination with the beta1 subinut (SCN1B). In contrast, cells expressing the mutant channels did not show any activation of inward current with or without the beta1 subunit. Culturing transfected cells at 25 degrees C did not restore the Na+ channel activity of the mutant protein. Transient expression of WT and mutant Na+ channels in the form of GFP fusion proteins in COS-7 cells indicated protein expression in the cytosol. But in contrast to WT channels were not associated with the plasma membrane.nnnCONCLUSIONSnThe SCN5A/5280delG mutation results in the translation into non-function channel proteins that do not reach the plasma membrane. This could explain the cardiac conduction defects in patients carrying the mutation.

Monomorphic Ventricular Tachycardia Due to Brugada Syndrome Successfully Treated by Hydroquinidine Therapy in a 3‐Year‐Old Child

Mutations in the SCN5A gene can cause Brugada syndrome, a genetically inherited form of idiopathic ventricular fibrillation. We describe the case of a 3‐year‐old child with a structurally normal heart presenting with monomorphic ventricular tachycardia. Her electrocardiogram suggested a Brugada syndrome and the diagnosis was confirmed by the identification of a Brugada syndrome in her mother and in two other family members. Genetic study led to the identification of a c.2516T→C SCN5A mutation. The child was treated with quinidine therapy without recurrence of arrhythmic events for a time period of 16 months.

Clinical characteristics of a familial inherited Myxomatous valvular dystrophy mapped to Xq28

OBJECTIVESnThe purpose of this study was to describe the phenotypic characteristics of an inherited myxomatous valvular dystrophy mapped to Xq28.nnnBACKGROUNDnMyxomatous valve dystrophies are a frequent cause of valvular diseases, the most common being idiopathic mitral valve prolapse. They form a group of heterogeneous diseases difficult to subclassify. The first mapping of the gene for a myxoid valvular dystrophy to Xq28 allowed investigation of the phenotype of affected members in a large family and characterization of the disease.nnnMETHODSnAmong the 318 members in the pedigree, 89 agreed to participate in this study. Phenotypic characteristics were investigated using clinical examination, transthoracic echocardiography and biological analysis (F.VIII activity). Genetic status was based on haplotype analysis.nnnRESULTSnAmong 46 males, 9 were hemizygous to the mutant allele and had an obvious mitral and/or aortic myxomatous valve defect, and 4 had undergone valvular surgery. All had typical mitral valve prolapse associated in six cases with moderate to severe aortic regurgitation. The valve defect cosegregated with mild hemophilia A (F.VIII activity = 0.32 +/- 0.05). The 37 remaining males had normal valves and normal F.VIII activity. Heterozygous women were identified on the basis of their haplotypes. Among the 17 women heterozygous to the mutant allele, moderate mitral regurgitation was present in 8, associated with mild mitral valve prolapse in 1 and aortic regurgitation in 3, whereas 2 women had isolated mild aortic regurgitant murmur. In heterozygotes, the penetrance value was 0.60 but increased with age.nnnCONCLUSIONnX-linked myxomatous valvular disease is characterized by mitral valve dystrophy frequently associated with degeneration of the aortic valves affecting males and, to a lower severity, females. The first localization of a gene for myxomatous valvular diseases is the first step for the subclassification of these diseases.

Filamin-A-Related Myxomatous Mitral Valve Dystrophy: Genetic, Echocardiographic and Functional Aspects

Myxomatous dystrophy of the cardiac valves is a heterogeneous group of disorders, including syndromic diseases such as Marfan syndrome and isolated valvular diseases. Mitral valve prolapse, the most common form of this disease, is presumed to affect approximately 2% to 3% of the population and remains one of the most common causes of valvular surgery. During the past years, important effort has been made to better understand the pathophysiological basis of mitral valve prolapse. Autosomal-dominant transmission is the usual inheritance with reduced penetrance and variable expressivity. Three loci have been mapped to chromosomes 16p11-p12, 11p15.4 and 13q31-32, but the underlying genetic defects are not currently known. An X-linked recessive form has been originally described by Monteleone and Fagan in 1969. Starting from one large French family and three smaller other families in which MVP was transmitted with an X-linked pattern, we have been able to identify three filamin A mutations p.Gly288Arg and p.Val711Asp and a 1,944-bp genomic deletion coding for exons 16 to 19. In this review, we describe the genetic, echocardiographic and functional aspects of the filamin-A-related myxomatous mitral valve dystrophy.

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

AIMSnThe natural history of congenital or childhood non-immune, isolated atrioventricular (AV) block is poorly defined.nnnMETHODS AND RESULTSnWe 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%).nnnCONCLUSIONnIn this large multicentre study, the long-term outcome of congenital or childhood non-immune, isolated AV block was favourable, regardless of the patients age at the time of diagnosis. No patient died or developed DCM, and pacemaker-related complications were few.