Neuromuscular Disorders

Editorial Board

2012-06-01

Paroxysmal neuromyotonia: A new sporadic channelopathy

2012-02-06

Abstract: Neuromyotonia is a heterogeneous group of genetic and autoimmune channelopathies resulting in hyperexcitability of peripheral nerves. We report an unusual case of neuromyotonia, which to our knowledge has not been previously described. The patient developed intermittent attacks of severe painful muscle stiffness accompanied by sweating, myokymia and raised serum creatine kinase. Genetic analysis of KCNA1, KCNQ2 and SCN4A genes did not identify pathogenic mutation. Serum voltage-gated potassium channel antibody was also negative. He was successfully treated with acetazolamide and carbamazepine. This appears to be a new neuromuscular disease, “paroxysmal neuromyotonia”, the etiology of which is still unknown.

Cerebral and muscle MRI abnormalities in myotonic dystrophy

2012-01-30

Abstract: Pathophysiological mechanisms underlying the clinically devastating CNS features of myotonic dystrophy (DM) remain more enigmatic and controversial than do the muscle abnormalities of this common form of muscular dystrophy. To better define CNS and cranial muscle changes in DM, we used quantitative volumetric and diffusion tensor MRI methods to measure cerebral and masticatory muscle differences between controls (n=5) and adults with either congenital (n=5) or adult onset (n=5) myotonic dystrophy type 1 and myotonic dystrophy type 2 (n=5). Muscle volumes were diminished in DM1 and strongly correlated with reduced white matter integrity and gray matter volume. Moreover, correlation of reduced fractional anisotropy (white matter integrity) and gray matter volume in both DM1 and DM2 suggests that these abnormalities may share a common underlying pathophysiological mechanism. Further quantitative temporal and spatial characterization of these features will help delineate developmental and progressive neurological components of DM, and help determine the causative molecular and cellular mechanisms.

Skeletal muscle involvement in myotonic dystrophy type 2. A comparative muscle ultrasound study

2012-03-14

Abstract: This study determines the presence and extent of muscle changes in 31 myotonic dystrophy type 2 (DM2) patients detected by muscle ultrasound. Results were compared to 31 adult-onset myotonic dystrophy type 1 patients (DM1) and healthy controls. Furthermore, we tested the hypothesis that structural muscle changes correlate with age, quantitative muscle force and serum creatine kinase in both disorders. In DM2 all seven examined muscles (right masseter muscle, right and left biceps brachii, right and left forearm flexors, right rectus femoris, and left tibialis anterior muscle) showed increased mean echo intensities (p⩽0.001). Atrophy of the masseter muscle and rectus femoris were both found in 23% of DM2 patients. Muscle thickness was significantly more decreased in the elbow flexors in DM2 compared to DM1. Echo intensity sum score correlated positively with age in DM2 (r=0.57, p=0.001) and negatively with muscle force (r=0.36, p=0.048). We conclude that all tested muscles are affected and structurally abnormal in DM2 patients. Proximal arm muscles are more affected in DM2 compared to DM1, which corresponds to clinical findings.

Normal height and weight in a series of ambulant Duchenne muscular dystrophy patients using the 10day on/10day off prednisone regimen

2012-03-05

Abstract: Prednisone treatment delays the progressive course of Duchenne muscular dystrophy. The aim of this study was to determine the influence of the 10day on/10day off treatment on height and weight. We retrospectively reviewed the growth and weight charts of Duchenne patients born between 1988 and 2006 (patients between 4 and 9years old, being able to walk in the home situation). Forty-seven patients were eligible for further analysis and divided into two groups: 33 patients treated with prednisone and 14 non-prednisone treated patients. Results of a median follow-up of 57months (range 27–146) are described. By using linear mixed models this study demonstrates that height and body mass index in prednisone-treated patients with 10/10 regimen are not significantly different compared to untreated patients. We cautiously conclude that the alternating prednisone regimen has no apparent side effects on weight and height in the ambulatory phase of Duchenne muscular dystrophy.

Two common mutations (p.Gln832X and c.663+1G>C) account for about a third of the DYSF mutations in Korean patients with dysferlinopathy

2012-02-01

Abstract: Dysferlinopathy refers to autosomal recessive muscular dystrophies caused by mutations in dysferlin gene (DYSF). It includes two major distinct disorders, Miyoshi myopathy and limb-girdle muscular dystrophy type 2B. Twenty-three Korean patients were recruited. Full sequence analysis of DYSF detected 10 novel and 9 known mutations. The p.Gln832X showed the highest allele frequency (10/46) as a unique recurrent mutation among Korean population, and two common mutations (p.Gln832X and c.663+1G>C) accounted for 34.8% of the identified mutations. Korean DYSF mutations appeared to cluster in the N-terminal region. Notably, none of homozygous mutations was found in this study. Clinical features were similar to previous reports showing onset in early adulthood, high serum CK and inflammatory reactions on muscle pathology. In Miyoshi myopathy, gastrocnemius muscle was first affected on muscle CT scans, and anterior lower legs and thigh muscles were then affected with disease progression. Despite the genetic variety of DYSF mutations, clinical features were rather invariable among the patients.

Hereditary motor neuron disease in a large Norwegian family with a “H46R” substitution in the superoxide dismutase 1 gene

2012-04-04

Abstract: Mutant genes associated with Charcot Marie Tooth type 2, distal hereditary motor neuropathy and familial amyotrophic lateral sclerosis may cause overlapping clinical phenotypes. We performed whole genome linkage analysis, haplotype analysis, sequencing and detailed clinical and neurophysiological investigations in a large Norwegian kindred with a condition that clinically had been classified as Charcot Marie Tooth type 2. The mutation c.140A>G, p.His47Arg (alias p.His46Arg or H46R) in the superoxide dismutase 1 gene (SOD1) segregated with the disease. The patients present a hereditary motor neuropathy-like clinical picture and long survival (mean 29years). To our knowledge, this is the first extensive report describing a large non-Japanese kindred. The prognostic implications of the condition seen in this family have little in common with what is normally associated with sporadic amyotrophic lateral sclerosis and illustrates the complexity of the genetic etiology of lower motor neuron disease.

Relative frequency of congenital muscular dystrophy subtypes: Analysis of the UK diagnostic service 2001–2008

2012-04-05

Abstract: The Dubowitz Neuromuscular Centre is the UK National Commissioning Group referral centre for congenital muscular dystrophy (CMD). This retrospective review reports the diagnostic outcome of 214 UK patients referred to the centre for assessment of ‘possible CMD’ between 2001 and 2008 with a view to commenting on the variety of disorders seen and the relative frequency of CMD subtypes in this patient population. A genetic diagnosis was reached in 53 of 116 patients fulfilling a strict criteria for the diagnosis of CMD. Within this group the most common diagnoses were collagen VI related disorders (19%), dystroglycanopathy (12%) and merosin deficient congenital muscular dystrophy (10%). Among the patients referred as ‘possible CMD’ that did not meet our inclusion criteria, congenital myopathies and congenital myasthenic syndromes were the most common diagnoses. In this large study on CMD the diagnostic outcomes compared favourably with other CMD population studies, indicating the importance of an integrated clinical and pathological assessment of this group of patients.

Sniff nasal inspiratory pressure and sleep disordered breathing in childhood neuromuscular disorders

2012-03-05

Abstract: The ease of sniff nasal inspiratory pressure testing may extend application of respiratory muscle assessment to younger and cognitively-impaired children. We sought to quantify sniff nasal inspiratory pressure in childhood neuromuscular disorders, and to correlate this measure with conventional pulmonary function tests and overnight polysomnography. Thirty children (mean 9.7±3.8years, range 4.3–16.5years) with diagnosed neuromuscular disorders (Duchenne muscular dystrophy, spinal muscular atrophy, Becker muscular dystrophy, congenital myopathy, facioscapulohumeral muscular dystrophy, myotonic dystrophy, multi-minicore disease) underwent assessment. Thirty-seven percent displayed cognitive impairment. Those with neuromuscular disorders were then compared with 32 volunteer age- and gender-matched controls (mean 10.9±2.9years, range 6.6–17.2years) with normal respiratory function. Twenty-three children with neuromuscular disorders also underwent overnight polysomnography. Children with neuromuscular disorders demonstrated significantly impaired sniff nasal inspiratory pressure, maximal inspiratory pressure, FEV1 and FVC (p<0.05). A positive correlation was identified between daytime sniff nasal inspiratory pressure and maximal inspiratory pressure (r=0.58), FEV1 (r=0.55) and FVC (r=0.46), though not with polysomnography variables (respiratory disturbance index, nadir SpO2, peak CO2). Moderate prevalence of nocturnal hypoxia was observed, and 32% of children demonstrated sleep disordered breathing. Sniff nasal inspiratory pressure assessment was well tolerated, representing a promising surrogate measure for assessment of respiratory function in childhood neuromuscular disorders.

Rippling muscle disease and facioscapulohumeral dystrophy-like phenotype in a patient carrying a heterozygous CAV3 T78M mutation and a D4Z4 partial deletion: Further evidence for “double trouble” overlapping syndromes

2012-01-16

Abstract: We report the first case of a heterozygous T78M mutation in the caveolin-3 gene (CAV3) associated with rippling muscle disease and proximal myopathy. The patient displayed also bilateral winged scapula with limited abduction of upper arms and marked asymmetric atrophy of leg muscles shown by magnetic resonance imaging. Immunohistochemistry on the patient’s muscle biopsy demonstrated a reduction of caveolin-3 staining, compatible with the diagnosis of caveolinopathy. Interestingly, consistent with the possible diagnosis of FSHD, the patient carried a 35kb D4Z4 allele on chromosome 4q35. We discuss the hypothesis that the two genetic mutations may exert a synergistic effect in determining the phenotype observed in this patient.

Necklace fibers as histopathological marker in a patient with severe form of X-linked myotubular myopathy

2012-01-24

Abstract: X-linked myotubular myopathy due to mutations in the MTM1 gene is classically characterized by a severe neonatal phenotype and a typical muscle biopsy presenting globular and centrally located nuclei in muscle myofibers. Recently, four patients with mild late-onset form have been described, a male with a hemizygous mutation and three females with heterozygous mutations in the MTM1 gene. The muscle biopsies were performed at 13–35years of age and a new histological marker, the necklace fibers, was described. Here, we report two siblings with the pathogenic c.664 C>T mutation in the MTM1 gene, presenting a severe muscle weakness and respiratory impairment requiring ventilatory support since the first months of life until death, at the age of 36months and 5months. In the older brother the muscle biopsy, performed at the age of 30months, showed almost 100% of necklace fibers, which were not present in the younger one submitted to muscle biopsy at 5months of age. Our findings confirm the necklace fibers can be a histopathological finding of MTM1 myopathies, even in the severe neonatal form, and suggest that the necklace fibers appear or increase in number over time.

Fetal acetylcholine receptor inactivation syndrome and maternal myasthenia gravis: A case report

2012-02-10

Abstract: Fetal acetylcholine receptor inactivation syndrome is a rare condition occurring in newborns of myasthenic mothers, characterized by bulbar and facial weakness after recovery from the generalized muscle weakness. Antibodies against fetal subunit of acetylcholine receptor seem to have a pathogenetic role leading to long-lasting injury in vulnerable muscle groups. We report a girl, born to a myasthenic mother, who presented with this peculiar phenotype associated with high titers of antibodies specific to the fetal acetylcholine receptor. Although the infant had partial clinical improvement she died prematurely of aspiration pneumonia. We believe that this is a rare but possibly unrecognized condition that should be considered in newborns with persistent myasthenic features even in asymptomatic mothers, and clinicians should consider supportive intervention to avoid fatal complications.

Role of serotonergic system in the pathogenesis of fibrosis in canine idiopathic inflammatory myopathies

2012-03-09

Abstract: Idiopathic inflammatory myopathies are muscle diseases characterized by inflammation, necrosis, and fibrosis. The neurotransmitter serotonin (5-HT) has been shown to promote fibrosis in many tissues and organs by activating TGFβ-1 signaling. In this study, we evaluated the potential role of 5-HT in the pathogenesis of fibrosis in canine idiopathic inflammatory myopathies. Muscle biopsies from dogs affected by masticatory muscle myositis or polymyositis and from healthy dogs were processed for immunohistochemistry and Western blotting. The immunohistochemical analysis showed a strong expression of 5-HT in muscle tissues of affected dogs, whereas the amine was absent in the muscles of healthy dogs. Biochemical analysis showed increased expression levels of the selective 5-HT2A receptor in the muscle specimens of the most severely affected dogs versus controls. Further, increased phosphorylation levels of the TGFβ-1 signaling mediators SMAD2/3 and ERK1/2 were detected in tissue samples from affected dogs as compared to tissues from healthy dogs. Although further studies are needed, our findings highlight for the first time a potential role of 5-HT in the development of fibrosis in canine idiopathic inflammatory myopathies, thus supporting other evidence that 5-HT pro-fibrotic activity occurs via activation of TGFβ-1 signaling pathway.

Experimental validation of in silico predicted KCNA1, KCNA2, KCNA6 and KCNQ2 genes for association studies of peripheral nerve hyperexcitability syndrome in Jack Russell Terriers

Mario Van Poucke, An E. Vanhaesebrouck, Luc J. Peelman, Luc Van Ham — 2012-02-16

Abstract: KCNA1, KCNA2, KCNA6 and KCNQ2 are associated with peripheral nerve hyperexcitability in humans. In order to determine if these genes are also involved in Jack Russell Terriers with a similar syndrome characterized by myokymia and neuromyotonia, their predicted canine orthologs were first validated experimentally. They were found either incompletely or even incorrectly annotated, mainly due to gaps in the canine genomic sequence and insufficient transcript data. Canine KCNQ2 was found to contain 20 coding exons, of which three are not described in humans. It encodes for at least 14 different transcript variants in the frontal cortex of a single dog, of which only four are also described in humans. Mutation detection in Jack Russell Terriers diagnosed with peripheral nerve hyperexcitability revealed no pathogenetic relevant structural mutations. However, the four missense sequence variations and the 14 transcript variants of KCNQ2 will contribute to the study of the functional diversity of voltage-gated potassium channels.

186th ENMC International Workshop: Congenital myasthenic syndromes 24–26 June 2011, Naarden, The Netherlands

Amina Chaouch, David Beeson, Daniel Hantaï, Hanns Lochmüller — 2012-01-09

The ENMC hosted a group of 22 participants including parents, clinicians and scientists involved in the care or research of congenital myasthenic syndromes (CMS) patients. These represented different groups and centres from the United Kingdom, Germany, Spain, France, Bulgaria, Switzerland, and the United States. CMS are rare inherited disorders in which the safety margin of the neuromuscular transmission is compromised . Currently, full genetic testing for CMS is only available in 4 major centres (Rochester, Paris, Oxford, Munich) who have collectively diagnosed more than 1000 patients (). The objectives of the meeting were to provide an update on CMS both in the clinical and non-clinical domains and to promote more collaborative work.

ENMC Announcement

2012-06-01