Recessive RYR1 mutations cause unusual congenital myopathy with prominent nuclear internalization and large areas of myofibrillar disorganization.

AIMS: To report the clinical, pathological and genetic findings in a group of patients with a previously not described phenotype of congenital myopathy due to recessive mutations in the gene encoding the type 1 muscle ryanodine receptor channel (RYR1). METHODS: Seven unrelated patients shared a predominant axial and proximal weakness of varying severity, with onset during the neonatal period, associated with bilateral ptosis and ophthalmoparesis, and unusual muscle biopsy features at light and electron microscopic levels. RESULTS: Muscle biopsy histochemistry revealed a peculiar morphological pattern characterized by numerous internalized myonuclei in up to 51% of fibres and large areas of myofibrillar disorganization with undefined borders. Ultrastructurally, such areas frequently occupied the whole myofibre cross section and extended to a moderate number of sarcomeres in length. Molecular genetic investigations identified recessive mutations in the ryanodine receptor (RYR1) gene in six compound heterozygous patients and one homozygous patient. Nine mutations are novel and four have already been reported either as pathogenic recessive mutations or as changes affecting a residue associated with dominant malignant hyperthermia susceptibility. Only two mutations were located in the C-terminal transmembrane domain whereas the others were distributed throughout the cytoplasmic region of RyR1. CONCLUSION: Our data enlarge the spectrum of RYR1 mutations and highlight their clinical and morphological heterogeneity. A congenital myopathy featuring ptosis and external ophthalmoplegia, concomitant with the novel histopathological phenotype showing fibres with large, poorly delimited areas of myofibrillar disorganization and internal nuclei, is highly suggestive of an RYR1-related congenital myopathy.

Differentiating Emery-Dreifuss muscular dystrophy and collagen VI-related myopathies using a specific CT scanner pattern.

Bethlem myopathy and Ullrich congenital muscular dystrophy are part of the heterogeneous group of collagen VI-related muscle disorders. They are caused by mutations in collagen VI (ColVI) genes (COL6A1, COL6A2, and COL6A3) while LMNA mutations cause autosomal dominant Emery-Dreifuss muscular dystrophy. A muscular dystrophy pattern and contractures are found in all three conditions, making differential diagnosis difficult especially in young patients when cardiomyopathy is absent. We retrospectively assessed upper and lower limb muscle CT scans in 14 Bethlem/Ullrich patients and 13 Emery-Dreifuss patients with identified mutations. CT was able to differentiate Emery-Dreifuss muscular dystrophy from ColVI-related myopathies in selected thigh muscles and to a lesser extent calves muscles: rectus femoris fatty infiltration was selectively present in Bethlem/Ullrich patients while posterior thigh muscles infiltration was more prominently found in Emery-Dreifuss patients. A more severe fatty infiltration particularly in the leg posterior compartment was found in the Emery-Dreifuss group.

Four Caucasian patients with mutations in the fukutin gene and variable clinical phenotype.

Fukuyama congenital muscular dystrophy (FCMD) is frequent in Japan, due to a founder mutation of the fukutin gene (FKTN). Outside Japan, FKTN mutations have only been reported in a few patients with a wide spectrum of phenotypes from Walker-Warburg syndrome to limb-girdle muscular dystrophy (LGMD2M). We studied four new Caucasian patients from three unrelated families. All showed raised serum CK initially isolated in one case and muscular dystrophy. Immunohistochemical studies and haplotype analysis led us to search for mutations in FKTN. Two patients (two sisters) presented with congenital muscular dystrophy, mental retardation, and posterior fossa malformation including cysts, and brain atrophy at Brain MRI. The other two patients had normal intelligence and brain MRI. Sequencing of the FKTN gene identified three previously described mutations and two novel missense mutations. Outside Japan, fukutinopathies are associated with a large spectrum of phenotypes from isolated hyperCKaemia to severe CMD, showing a clear overlap with that of FKRP.

Arrhythmic sudden death in children.

Sudden death (SD) in childhood is rare, representing only 10% of paediatric mortality after one year of age. The individual risk is estimated between 1 in 20.000 and 1 in 50.000 per year. In case of a negative autopsy for cardiac morphologic anomalies, the most presumable cause remains a genetically-determined malignant primary ventricular arrhythmia. Rhythmic sudden cardiac death can be categorized as a complication of a cardiomyopathy (dilated or hypertrophic), or as a primary channelopathy without any structural heart disease. Primary ventricular arrhythmias include long QT syndrome, Brugada syndrome, short QT syndrome and Polymorphic Ventricular Tachycardia. The diagnosis of such syndromes relies upon specific ECG anomalies, personal history of family members, eventually echocardiography and drug challenge. For some of these diseases, morbid genes have been identified thus rendering possible the management of pre symptomatic or undiagnosed family members within specialized multidisciplinary teams. In case of sudden arrhythmic death in children, the parents and siblings must be examined Rescued sudden death exposes to a high risk of recurrence. In such patients, the automatic implantable defibrillator has dramatically improved survival.

Ex vivo correction of selenoprotein N deficiency in rigid spine muscular dystrophy caused by a mutation in the selenocysteine codon.

Premature termination of translation due to nonsense mutations is a frequent cause of inherited diseases. Therefore, many efforts were invested in the development of strategies or compounds to selectively suppress this default. Selenoproteins are interesting candidates considering the idiosyncrasy of the amino acid selenocysteine (Sec) insertion mechanism. Here, we focused our studies on SEPN1, a selenoprotein gene whose mutations entail genetic disorders resulting in different forms of muscular diseases. Selective correction of a nonsense mutation at the Sec codon (UGA to UAA) was undertaken with a corrector tRNA(Sec) that was engineered to harbor a compensatory mutation in the anticodon. We demonstrated that its expression restored synthesis of a full-length selenoprotein N both in HeLa cells and in skin fibroblasts from a patient carrying the mutated Sec codon. Readthrough of the UAA codon was effectively dependent on the Sec insertion machinery, therefore being highly selective for this gene and unlikely to generate off-target effects. In addition, we observed that expression of the corrector tRNA(Sec) stabilized the mutated SEPN1 transcript that was otherwise more subject to degradation. In conclusion, our data provide interesting evidence that premature termination of translation due to nonsense mutations is amenable to correction, in the context of the specialized selenoprotein synthesis mechanism.

Dynamin 2-related centronuclear myopathy: clinical, histological and genetic aspects of further patients and review of the literature.

Centronuclear myopathy (CNM) is a slowly progressive congenital myopathy with characteristic histopathological findings of chains of centrally located myonuclei in a large number of muscle fibers. Recently, different missense mutations in the dynamin 2 gene (DNM2, 19p13.2) have been shown to cause autosomal dominant CNM. We re-evaluated patients with a histopathological diagnosis of CNM and report on the clinical phenotype, the biopsy findings and the genetic results of these patients and review the current literature. Two of the three patients showed an unusually late disease onset (> 40 years). Interestingly, intramuscular nerve fascicles found in the muscle biopsy of a patient harboring the E368K DNM2 mutation contained nerve fibers with disproportionately thin myelin sheaths. Schwann cells of unmyelinated nerve fibers showed abnormal plasma membrane and basal lamina protrusions, indicating peripheral nerve involvement.

New POMT2 mutations causing congenital muscular dystrophy: identification of a founder mutation.

BACKGROUND: Dystroglycanopathies are a group of congenital muscular dystrophies (CMDs) with autosomal recessive inheritance, often associated with CNS and ocular involvement. They are characterized by the abnormal glycosylation of alpha-dystroglycan, and caused by mutations in at least six genes encoding enzymes: FKTN, POMGNT1, POMT1, POMT2, FKRP, and LARGE. POMT2 mutations have recently been identified in Walker-Warburg syndrome and in a milder muscle-eye-brain disease-like form. METHODS: We studied mentally retarded patients with CMD, analyzed POMT2 by sequencing the coding regions, and also performed a haplotype analysis in all patients and their family members carrying the new POMT2 mutation. RESULTS: We report three novel POMT2 mutations. One of these, p.Tyr666Cys, was homozygous in two unrelated patients and in a compound heterozygous state in others. All patients showed severe diffuse muscle weakness, microcephaly, severe mental retardation, and marked lordoscoliosis with hyperextended head. Elevated CK levels, cerebral cortical atrophy, and cerebellar vermis hypoplasia were constant findings. Mild cardiac abnormalities, focal white matter abnormalities, or partial corpus callosum hypoplasia were detected in single cases. Eye involvement was absent or mild. By genotype analysis, we defined a distinct 170kb haplotype encompassing POMT2 and shared by all the subjects harboring the mutation p.Tyr666Cys. CONCLUSIONS: Our results broaden the clinical spectrum associated with POMT2 mutations, which should be considered in patients with CMD associated with microcephaly, and severe mental retardation with or without ocular involvement.

[The Jervell and Lange-Nielsen syndrome. Natural history, molecular basis and clinical outcome]. / Syndrome de Jervell et Lange-Nielsen. Histoire naturelle, bases moléculaires et devenir clinique.

UNLABELLED: Data on the Jervell and Lange-Nielsen syndrome (JLN), the long QT syndrome (LQTS) variant associated with deafness and caused by homozygous or compound heterozygous mutations on the KCNQ1 or on the KCNE1 genes encoding the IKs current, are still largely based on case reports. We analyzed data from 186 JLN patients obtained from the literature (31%) and from individual physicians (69%). Most patients (86%) had cardiac events and 50% were symptomatic already by age 3. Their QTc was markedly prolonged (557 +/- 65 ms). Most of the arrhythmic events (95%) were triggered by emotions or exercise. Females are at lower risk for cardiac arrest and sudden death (CA/SD). A QTc>550 ms and history of syncope during the first year of life are independent predictors of subsequent CA/SD. Most mutations (90.5%) are on the KCNQ1 gene; mutations on the KCNE1 gene are associated with a more benign course. beta-blockers have only partial efficacy as 51% of the patients had events despite therapy and 29% had CA/SD. CONCLUSIONS: JLN syndrome is a most severe variant of LQTS, with a very early onset, major QTc prolongation, and is not well responsive to beta-blockers. Subgroups at relatively lower risk for CA/SD are identifiable and include females, patients with a QTc pound550 ms, without events in the first year of life, and with mutations on KCNE1. Early therapy with ICDs has to be considered.

Confirmation of associations between ion channel gene SNPs and QTc interval duration in healthy subjects.

Population-based association studies have identified several polymorphic variants in genes encoding ion channel subunits associated with the electrocardiographic heart-rate-corrected QT (QTc) length in healthy populations of Caucasian origin (KCNH2 rs1,805,123 (K897 T) and rs3,815,459, SCN5A rs1,805,126 (D1,819D), 1,141-3 C>A, rs1,805,124 (H558R), and IVS24+116 G>A, KCNQ1 rs757,092, KCNE1 IVS2-128 G>A and rs1,805,127 (G38S), and KCNE2 rs2,234,916 (T8A)). However, few of these results have been replicated in independent populations. We tested the association of SNPs KCNQ1 rs757,092, KCNH2 rs3,815,459, SCN5A IVS24+116 G>A, KCNE1 IVS2-128 G>A and KCNE2 rs2,234,916 with QTc length in two groups of 200 subjects presenting the shortest and the longest QTc from a cohort of 2,008 healthy subjects. All polymorphisms were in Hardy-Weinberg equilibrium in both groups. The minor allele SCN5A IVS24+116 A was more frequent in the group of subjects with the shortest QTc, whereas the minor alleles KCNQ1 rs757,092 G and KCNH2 rs3,815,459 A were more frequent in the group with the longest QTc. There was no significant difference for KCNE1 IVS2-128 G>A and KCNE2 rs2,234,916 between the two groups. Haplotype analysis showed a twofold increased risk of QTc lengthening for carriers of the haplotype, combining alleles C and A of the two common KCNE1 SNPs, IVS2-129 C>T (rs2,236,609) and rs1,805,127 (G38S), respectively. In conclusion, our study confirms the reported associations between QTc length and KCNQ1 rs757,092 and KCNH2 rs3,815,459.

Muscle imaging in dominant core myopathies linked or unlinked to the ryanodine receptor 1 gene.

OBJECTIVE: To characterize the muscle involvement of patients with central core disease (CCD) caused by mutations in the ryanodine receptor 1 gene (RYR1) and to compare these findings with those from patients with core myopathies unlinked to the RYR1 gene. METHODS: We performed a systematic muscular imaging assessment in 11 patients with an RYR1 gene mutation and compared these findings with those of 5 patients from two unrelated families with autosomal dominant core myopathies not linked to RYR1, ACTA1, or MYH7 gene loci. RESULTS: All patients with RYR1 CCD had a characteristic pattern with predominant involvement of the gluteus maximus, adductor magnus, sartorius, vastus intermediolateralis, soleus, and lateral gastrocnemius muscles. In contrast, muscle CT in the first family not linked to RYR1 showed predominant affection of the gluteus minimus and hamstring muscles, whereas the second family presented with predominant involvement of the gluteus minimus, vastus intermediolateralis, tibialis anterior, and medial gastrocnemius muscles. In addition to muscle imaging data, we present detailed information on the clinical and pathologic findings of these novel phenotypes of core myopathies not linked to RYR1. CONCLUSIONS: Our data suggest genetic heterogeneity in autosomal dominant core myopathies and the existence of additional unidentified genes.

[Molecular genetics of cardiac arrhythmias]. / Génétique moléculaire des arythmies cardiaques.

INTRODUCTION: Recent progress in molecular biology led to the identification of the genes involved in various cardiac arrhythmias causing syncope and sudden death in young people. EXEGESIS: This article briefly describes the clinical features and the genes associated with the congenital long QT syndrome, the short QT syndrome, Brugada's syndrome, catecholaminergic polymorphic ventricular tachycardias and arrhythmogenic right ventricular dysplasia. CONCLUSION: Identification of genetic variations that cause cardiac tachyarrhythmias can help to identify at risk-patients and to propose clinical follow-up and preventive therapy. Further studies are needed to discover other cardiac genetic disorders and to understand cellular mechanisms involved in these diseases.

Novel mutations in LAMA2 gene responsible for a severe phenotype of congenital muscular dystrophy in two Tunisian families.

Congenital muscular dystrophies are a group of common genetically determined disorders often transmitted with a recessive mode of inheritance. In recent years, several deficiencies of proteins from the muscle membrane, extra cellular matrix, sarcomere, muscle cytosol and the nucleus have been described to cause CMD. The occidental type of CMD (MDC1A) in which the primary defect is a deficiency in laminin alpha2 chain (merosin) encoded by LAMA2 gene, accounts for 30-40% of cases. The clinical course of CMD with complete laminin alpha2 chain deficiency may be variable but most often; severe forms characterized by hypotonia at birth, profound muscle weakness, marked delay in motor milestones are observed. Since the identification of the first LAMA2 gene mutations leading to merosin deficiency in 1995, several mutations have subsequently been reported in many exons of this gene without any "hotspot" region. In this work, we report two novel homozygous mutations c.8005delT and c.8244+1G>A in the LAMA2 gene in four Tunisian patients with a severe MDC1A phenotype belonging to two unrelated consanguineous families.

Catecholaminergic polymorphic ventricular tachycardia: RYR2 mutations, bradycardia, and follow up of the patients.

BACKGROUND: The aim of the study was to assess underlying genetic cause(s), clinical features, and response to therapy in catecholaminergic polymorphic ventricular tachycardia (CPVT) probands. METHODS AND RESULTS: We identified 13 missense mutations in the cardiac ryanodine receptor (RYR2) in 12 probands with CPVT. Twelve were new, of which two are de novo mutations. A further 11 patients were silent gene carriers, suggesting that some mutations are associated with low penetrance. A marked resting sinus bradycardia off drugs was observed in all carriers. On beta blocker treatment, 98% of the RYR2 mutation carriers remained symptom free with a median follow up of 2 (range: 2-37) years. CONCLUSION: CPVT patients with RYR2 mutation have bradycardia regardless of the site of the mutation, which could direct molecular diagnosis in (young) patients without structural heart disease presenting with syncopal events and a slow heart rate but with normal QTc at resting ECG. Treatment with beta blockers has been very effective in our CPVT patients during initial or short term follow up. Given the risk of sudden death and the efficacy of beta blocker therapy, the identification of large numbers of RYR2 mutations thus calls for genetic screening, early diagnosis, and subsequent preventive strategies.

[Catecholinergic ventricular tachycardia in children]. / Tachycardies ventriculaires catécholergiques chez l'enfant.

Catecholinergic ventricular tachycardia is an adrenergic induced polymorphic ventricular arrhythmia. It occurs in infancy and is responsible for syncope and sudden death in the absence of any morphological cardiac abnormality. Without treatment the mortality in catecholinergic ventricular tachycardia is very high. We report genetic and clinical data from 25 cases of catecholinergic ventricular tachycardia referred with syncope (n=19) or resuscitated sudden death during exercise (n=6). A family history from the 25 families identified 41 apparent subjects considered as being clinically affected, with an average age of 30 +/- 10 years (11 to 62 years). Analysis of the RyR2 gene showed mutations in 13 of the 25 cases and in 39 of apparent subjects. With betablocker treatment (nadolol: 1.6 +/- 0.15 mg/kg), 96% of patients remained asymptomatic over an average follow-up of between 7.5 +/- 1.5 years, although some of them continued to display polymorphic ventricular extrasystoles on exercise. Nevertheless, 12% of the cases suffered sudden death or further syncope during follow-up. An automatic defibrillator was implanted in 2 patients who had a RyR2 mutation. High dose betablockers are effective in preventing serious rhythm disturbance in children. In adolescence, implanting an automatic defibrillator should be discussed in cases with a history of syncope or resuscitated sudden death. We confirm the importance of genetic studies in these families at high risk of sudden death.

Two patients with 'Dropped head syndrome' due to mutations in LMNA or SEPN1 genes.

Dropped head syndrome is characterized by severe weakness of neck extensor muscles with sparing of the flexors. It is a prominent sign in several neuromuscular conditions, but it may also be an isolated feature with uncertain aetiology. We report two children in whom prominent weakness of neck extensor muscles is associated with mutations in lamin A/C (LMNA) and selenoprotein N1 (SEPN1) genes, respectively. This report expands the underlying causes of the dropped head syndrome which may be the presenting feature of a congenital muscular dystrophy.

Giant axonal neuropathy: clinical and genetic study in six cases.

BACKGROUND: Giant axonal neuropathy (GAN) is a severe recessive disorder characterised by variable combination of progressive sensory motor neuropathy, central nervous system (CNS) involvement, and "frizzly" hair. The disease is caused by GAN gene mutations on chromosome 16q24.1. AIMS: To search for GAN gene mutations in Turkish patients with GAN and characterise the phenotype associated with them. METHODS: Linkage and mutation analyses were performed in six affected patients from three consanguineous families. These patients were also investigated by cranial magnetic resonance imaging (MRI) and electroencephalography (EEG). Electromyography (EMG) was performed in heterozygous carriers from family 1 and family 3. RESULTS: Linkage to 16q24.1 was confirmed by haplotype analysis. GAN mutations were identified in all families. Family 1 had the R293X mutation, previously reported in another Turkish family. Families 2 and 3, originating from close geographical areas, shared a novel mutation, 1502+1G>T, at the donor splice site of exon 9. All patients displayed a common phenotype, including peripheral neuropathy, cerebellar ataxia, and frizzly hair. Cranial MRI showed diffuse white matter abnormalities in two patients from family 1 and the patient from family 3, and minimal white matter involvement in the patient from family 2. EMG of a heterozygous R293X mutation carrier showed signs of mild axonal neuropathy, whereas a 1502+1G>T mutation carrier had normal EMG. EEG abnormalities were found in three patients. CONCLUSION: These findings highlight the association of CNS involvement, in particular white matter abnormalities, with peripheral neuropathy in GAN. The phenotypical consequences of both mutations (when homozygous) were similar.

Clinical and histopathological aspects of central core disease associated and non-associated with RYR1 locus.

We analysed the clinical, histochemical, ultrastructural and genetic data of patients affected by central core disease (CCD) studied during the last 20 years. From a total series of 86 CCD-families, we have identified 46 CCD families with RYR1 mutations (16 autosomal dominant, 8 autosomal recessive, 17 sporadic cases and 5 de novo mutations). Out of the other 40 CCD families, the RyR1 gene was entirely excluded in 7 families, by cDNA sequencing or linkage analysis, indicating a genetic heterogeneity of CCD.