Ephedrine treatment in congenital myasthenic syndrome due to mutations in DOK7

β2-Adrenoceptor agonists as novel, safe and potentially effective therapies for Amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a chronic and progressive neuromuscular disease for which no cure exists and better treatment options are desperately needed. We hypothesize that currently approved β2-adrenoceptor agonists may effectively treat the symptoms and possibly slow the progression of ALS. Although β2-agonists are primarily used to treat asthma, pharmacologic data from animal models of neuromuscular diseases suggest that these agents may have pharmacologic effects of benefit in treating ALS. These include inhibiting protein degradation, stimulating protein synthesis, inducing neurotrophic factor synthesis and release, positively modulating microglial and systemic immune function, maintaining the structural and functional integrity of motor endplates, and improving energy metabolism. Moreover, stimulation of β2-adrenoceptors can activate a range of downstream signaling events in many different cell types that could account for the diverse array of effects of these agents. The evidence supporting the possible therapeutic benefits of β2-agonists is briefly reviewed, followed by a more detailed review of clinical trials testing the efficacy of β-agonists in a variety of human neuromuscular maladies. The weight of evidence of the potential benefits from treating these diseases supports the hypothesis that β2-agonists may be efficacious in ALS. Finally, ways to monitor and manage the side effects that may arise with chronic administration of β2-agonists are evaluated. In sum, effective, safe and orally-active β2-agonists may provide a novel and convenient means to reduce the symptoms of ALS and possibly delay disease progression, affording a unique opportunity to repurpose these approved drugs for treating ALS, and rapidly transforming the management of this serious, unmet medical need.

Ephedrine as add-on therapy for patients with myasthenia gravis: protocol for a series of randomised, placebo-controlled n-of-1 trials

INTRODUCTION

Myasthenia gravis (MG), a rare neuromuscular disease, is often initially treated using acetylcholinesterase inhibitors. Patients who do not respond adequately depend on the use of corticosteroids or other immunosuppressive medication, but these may have serious side effects. Clinical observations suggest that ephedrine can diminish, postpone or even prevent the need for immunosuppressive therapy when added to acetylcholinesterase inhibitors or low-dose prednisone. In the Netherlands, ephedrine is not licensed for MG nor is reimbursement guaranteed. MG is a rare condition, and ephedrine might be indicated only in a subset of patients. Thus, randomised controlled trials comparing large groups are difficult to conduct. We, therefore, aim to aggregate data from a small series of n-of-1 trials (also known as single patient trials) to assess the effect of ephedrine as add-on treatment for MG.

METHODS AND ANALYSIS

Single-centre, placebo-controlled, double-blind, randomised, multiple crossover n-of-1 studies in 4 adult patients with generalised MG who show inadequate improvement on pyridostigmine and/or immunosuppressive drugs. Each n-of-1 trial has 3 cycles of two 5-day intervention periods.

TREATMENT

25 mg ephedrine or placebo, twice daily.

MAIN OUTCOME MEASURE

Quantitative Myasthenia Gravis (QMG) test.

STATISTICAL ANALYSIS

fixed effects linear model for QMG for all patients combined.

SECONDARY OUTCOME MEASURES

Clinical: effects on MG-Composite and MG-Activities of Daily Living (MG-ADL) scales; QMG at individual level; adverse events. Acceptability of trial design: number of patients eligible and enrolled; number of treatment cycles completed; patients' and caregivers' experiences.

ETHICS AND DISSEMINATION

This study was approved by the Medical Ethics Committee of Leiden University Medical Center, No. P14.108. Results of the trial will be reported in a peer-reviewed publication. Regulatory stakeholders will comment on the suitability of the trial for market authorisation and reimbursement purposes.

TRIAL REGISTRATION NUMBER

This study is registered under EudraCT number 2014-001355-23, protocol no. 40960, V.1.0, registration date 27 March 2014.

Ephedrine for myasthenia gravis, neonatal myasthenia and the congenital myasthenic syndromes

BACKGROUND

Myasthenia is a condition in which neuromuscular transmission is affected by antibodies against neuromuscular junction components (autoimmune myasthenia gravis, MG; and neonatal myasthenia gravis, NMG) or by defects in genes for neuromuscular junction proteins (congenital myasthenic syndromes, CMSs). Clinically, some individuals seem to benefit from treatment with ephedrine, but its effects and adverse effects have not been systematically evaluated.

OBJECTIVES

To assess the effects and adverse effects of ephedrine in people with autoimmune MG, transient neonatal MG, and the congenital myasthenic syndromes.

SEARCH METHODS

On 17 November 2014, we searched the Cochrane Neuromuscular Disease Group Specialized Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE. We also searched reference lists of articles, conference proceedings of relevant conferences, and prospective trial registers. In addition, we contacted manufacturers and researchers in the field.

SELECTION CRITERIA

We considered randomised controlled trials (RCTs) and quasi-RCTs comparing ephedrine as a single or add-on treatment with any other active treatment, placebo, or no treatment in adults or children with autoimmune MG, NMG, or CMSs.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study design and quality, and extracted data. We contacted study authors for additional information. We collected information on adverse effects from included articles, and contacted authors.

MAIN RESULTS

We found no RCTs or quasi-RCTs, and therefore could not establish the effect of ephedrine on MG, NMG and CMSs. We describe the results of 53 non-randomised studies narratively in the Discussion section, including observations of endurance, muscle strength and quality of life. Effects may differ depending on the type of myasthenia. Thirty-seven studies were in participants with CMS, five in participants with MG, and in 11 the precise form of myasthenia was unknown. We found no studies for NMG. Reported adverse effects included tachycardia, sleep disturbances, nervousness, and withdrawal symptoms.

AUTHORS' CONCLUSIONS

There was no evidence available from RCTs or quasi-RCTs, but some observations from non-randomised studies are available. There is a need for more evidence from suitable forms of prospective RCTs, such as series of n-of-one RCTs, that use appropriate and validated outcome measures.

Inherited disorders of the neuromuscular junction: an update

Congenital myasthenic syndromes (CMSs) are a group of heterogeneous inherited disorders caused by mutations in genes affecting the function and structure of the neuromuscular junction. This review updates the reader on established and novel subtypes of congenital myasthenia, and the treatment strategies for these increasingly heterogeneous disorders. The discovery of mutations associated with the N-glycosylation pathway and in the family of serine peptidases has shown that causative genes encoding ubiquitously expressed molecules can produce defects at the human neuromuscular junction. By contrast, mutations in lipoprotein-like receptor 4 (LRP4), a long-time candidate gene for congenital myasthenia, and a novel phenotype of myasthenia with distal weakness and atrophy due to mutations in AGRN have now been described. In addition, a pathogenic splicing mutation in a nonfunctional exon of CHRNA1 has been reported emphasizing the importance of analysing nonfunctional exons in genetic analysis. The benefit of salbutamol and ephedrine alone or combined with pyridostigmine or 3,4-DAP is increasingly being reported for particular subtypes of CMS.

A conceptual framework for evaluating impairments in myasthenia gravis

Background

Myasthenia gravis is characterized by weakness and fatigability of different muscle groups, including ocular, bulbar and the limbs. Therefore, a measure of disease severity at the impairment level in myasthenia needs to reflect all the relevant impairments, as well as their variations with activity and fatigue. We conducted a qualitative study of patients with myasthenia, to explore their experiences and related impairments, aimed at developing a conceptual framework of disease severity at the impairment level in myasthenia gravis.

Methods

Twenty patients representing the spectrum of disease participated in semi-structured interviews. Interviews were recorded and the transcripts were analyzed by content analysis using an inductive approach with line-by-line open coding. Themes were generated from these codes.

Results

Two main themes were identified: the severity of the impairments and fatigability (i.e., triggering or worsening of an impairment with activity). The impairments were further classified within body regions (ocular, bulbar and axial/limbs). Fatigability was described as a phenomenon affecting the whole body but also affecting specific impairments, and was associated with fluctuation of the symptoms. Patients were concerned that clinical examination at a single point in time might not reflect their true clinical state due to fatigability and fluctuations in severity.

Conclusions

This conceptual framework reflects the relevance of both severity and fatigability in understanding impairment-based disease severity in myasthenia. This framework could inform the development of impairment measures in myasthenia gravis.

Effects of the ß2-adrenoceptor agonist, albuterol, in a mouse model of anti-MuSK myasthenia gravis

The β2-adrenergic receptor agonist, albuterol, has been reported beneficial in treating several forms of congenital myasthenia. Here, for the first time, we examined the potential benefit of albuterol in a mouse model of anti-Muscle Specific Kinase (MuSK) myasthenia gravis. Mice received 15 daily injections of IgG from anti-MuSK positive patients, which resulted in whole-body weakness. At neuromuscular junctions in the tibialis anterior and diaphragm muscles the autoantibodies caused loss of postsynaptic acetylcholine receptors, and reduced the amplitudes of the endplate potential and spontaneous miniature endplate potential in the diaphragm muscle. Treatment with albuterol (8 mg/kg/day) during the two-week anti-MuSK injection series reduced the degree of weakness and weight loss, compared to vehicle-treated mice. However, the compound muscle action potential recorded from the gastrocnemius muscle displayed a decremental response in anti-MuSK-injected mice whether treated with albuterol or vehicle. Ongoing albuterol treatment did not increase endplate potential amplitudes compared to vehicle-treated mice nor did it prevent the loss of acetylcholine receptors from motor endplates. On the other hand, albuterol treatment significantly reduced the degree of fragmentation of endplate acetylcholine receptor clusters and increased the extent to which the remaining receptor clusters were covered by synaptophysin-stained nerve terminals. The results provide the first evidence that short-term albuterol treatment can ameliorate weakness in a robust mouse model of anti-MuSK myasthenia gravis. The results also demonstrate that it is possible for albuterol treatment to reduce whole-body weakness without necessarily reversing myasthenic impairment to the structure and function of the neuromuscular junction.

[Beneficial effects of 3,4-diaminopyridine in a 26-year-old woman with DOK7 congenital myasthenic syndrome who was originally diagnosed with facioscapulohumeral dystrophy]

We report a 26-year-old woman who had respiratory dysfunction and muscle weakness at birth and was diagnosed with facioscapulohumeral dystrophy at the age of 5. The extent of muscle weakness fluctuated daily or weekly and deteriorated in menstrual periods. At the age of 12, she noted improvements in symptoms when taking procaterol hydrochloride and began to take it regularly. After that, her condition stabilized. At the age of 26, she visited our hospital presenting with ptosis, muscle weakness in the face, trunk, and proximal limbs, and easy fatigability. Serum CK was normal; anti-acetylcholine receptor and anti-muscle specific tyrosine kinase antibodies were negative. A repetitive stimulation test in the trapezius muscle showed a waning phenomenon. Gene analysis for congenital myasthenic syndrome (CMS) revealed a new mutation in the DOK7 gene; the diagnosis of CMS was confirmed. Her symptoms worsened with ambenonium chloride but improved with 3,4-diaminopyridine. Our findings suggest that daily or weekly fluctuation and worsening with a menses in muscle weakness is an important diagnostic feature of CMS.

Alterations of cAMP-dependent signaling in dystrophic skeletal muscle

Autonomic regulation processes in striated muscles are largely mediated by cAMP/PKA-signaling. In order to achieve specificity of signaling its spatial-temporal compartmentation plays a critical role. We discuss here how specificity of cAMP/PKA-signaling can be achieved in skeletal muscle by spatio-temporal compartmentation. While a microdomain containing PKA type I in the region of the neuromuscular junction (NMJ) is important for postsynaptic, activity-dependent stabilization of the nicotinic acetylcholine receptor (AChR), PKA type I and II microdomains in the sarcomeric part of skeletal muscle are likely to play different roles, including the regulation of muscle homeostasis. These microdomains are due to specific A-kinase anchoring proteins, like rapsyn and myospryn. Importantly, recent evidence indicates that compartmentation of the cAMP/PKA-dependent signaling pathway and pharmacological activation of cAMP production are aberrant in different skeletal muscles disorders. Thus, we discuss here their potential as targets for palliative treatment of certain forms of dystrophy and myasthenia. Under physiological conditions, the neuropeptide, α-calcitonin-related peptide, as well as catecholamines are the most-mentioned natural triggers for activating cAMP/PKA signaling in skeletal muscle. While the precise domains and functions of these first messengers are still under investigation, agonists of β₂-adrenoceptors clearly exhibit anabolic activity under normal conditions and reduce protein degradation during atrophic periods. Past and recent studies suggest direct sympathetic innervation of skeletal muscle fibers. In summary, the organization and roles of cAMP-dependent signaling in skeletal muscle are increasingly understood, revealing crucial functions in processes like nerve-muscle interaction and muscle trophicity.

Clinical features of congenital myasthenic syndrome due to mutations in DPAGT1

BACKGROUND

A newly defined congenital myasthenic syndrome (CMS) caused by DPAGT1 mutations has recently been reported. While many other CMS-associated proteins have discrete roles localised to the neuromuscular junction, DPAGT1 is ubiquitously expressed, modifying many proteins, and as such is an unexpected cause of isolated neuromuscular involvement.

METHODS

We present detailed clinical characteristics of five patients with CMS caused by DPAGT1 mutations.

RESULTS

Patients have prominent limb girdle weakness and minimal craniobulbar symptoms. Tubular aggregates on muscle biopsy are characteristic but may not be apparent on early biopsies. Typical myasthenic features such as pyridostigmine and 3, 4- diaminopyridine responsiveness, and decrement on repetitive nerve stimulation are present.

CONCLUSIONS

These patients mimic myopathic disorders and are likely to be under-diagnosed. The descriptions here should facilitate recognition of this disorder. In particular minimal craniobulbar involvement and tubular aggregates on muscle biopsy help to distinguish DPAGT1 CMS from the majority of other forms of CMS. Patients with DPAGT1 CMS share similar clinical features with patients who have CMS caused by mutations in GFPT1, another recently identified CMS subtype.

[Congenital myasthenic syndromes: difficulties in the diagnosis, course and prognosis, and therapy--The French National Congenital Myasthenic Syndrome Network experience]

Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders caused by genetic defects affecting neuromuscular transmission and leading to muscle weakness accentuated by exertion. Three different aspects have been investigated by members of the national French CMS Network: the difficulties in making a proper diagnosis; the course and long-term prognosis; and the response to therapy, especially for CMS that do not respond to cholinesterase inhibitors. CMS diagnosis is late in most cases because of confusion with other entities such as: congenital myopathies, due to the frequent presentation in patients of myopathies such as permanent muscle weakness, atrophy and scoliosis, and the abnormalities of internal structure, diameter and distribution of fibers (type I predominance, type II atrophy) seen on biopsy; seronegative autoimmune myasthenia gravis, when CMS is of late onset; and metabolic myopathy, with the presence of lipidosis in muscle. The long-term prognosis of CMS was studied in a series of 79 patients recruited with the following gene mutations: CHRNA; CHRNE; DOK7; COLQ; RAPSN; AGRN; and MUSK. Disease-course patterns (progressive worsening, exacerbation, stability, improvement) could be variable throughout life in a given patient. DOK7 patients had the most severe disease course with progressive worsening: of the eight wheelchair-bound and ventilated patients, six had mutations of this gene. Pregnancy was a frequent cause of exacerbation. Anticholinesterase agents are the first-line therapy for CMS patients, except for cases of slow-channel CMS, COLQ and DOK7. In our experience, 3,4-DAP was a useful complement for several patients harboring CMS with AChR loss or RAPSN gene mutations. Ephedrine was given to 18 patients (eight DOK7, five COLQ, four AGRN and one RAPSN). Tolerability was good. Therapeutic responses were encouraging even in the most severely affected patients, particularly with DOK7 and COLQ. Salbutamol was a good alternative in one patient who was allergic to ephedrine.

A mouse model of the slow channel myasthenic syndrome: Neuromuscular physiology and effects of ephedrine treatment

In the slow channel congenital myasthenic syndrome mutations in genes encoding the muscle acetylcholine receptor give rise to prolonged ion channel activations. The resulting cation overload in the postsynaptic region leads to damage of synaptic structures, impaired neuromuscular transmission and fatigable muscle weakness. Previously we identified and characterised in detail the properties of the slow channel syndrome mutation εL221F. Here, using this mutation, we generate a transgenic mouse model for the slow channel syndrome that expresses mutant human ε-subunits harbouring an EGFP tag within the M3-M4 cytoplasmic region, driven by a ~1500 bp region of the CHRNB promoter. Fluorescent mutant acetylcholine receptors are assembled, cluster at the motor endplates and give rise to a disease model that mirrors the human condition. Mice demonstrate mild fatigable muscle weakness, prolonged endplate and miniature endplate potentials, and variable degeneration of the postsynaptic membrane. We use our model to investigate ephedrine as a potential treatment. Mice were assessed before and after six weeks on oral ephedrine (serum ephedrine concentration 89 ± 3 ng/ml) using an inverted screen test and in vivo electromyography. Treated mice demonstrated modest benefit for screen hang time, and in measures of compound muscle action potentials and mean jitter that did not reach statistical significance. Ephedrine and salbutamol show clear benefit when used in the treatment of DOK7 or COLQ congenital myasthenic syndromes. Our results highlight only a modest potential benefit of these β2-adrenergic receptor agonists for the treatment of the slow channel syndrome.

Salbutamol therapy in congenital myasthenic syndrome due to DOK7 mutation

INTRODUCTION

Salbutamol is a selective B2-adrenergic agonist, which has previously been described to be associated with partial improvement of myasthenia gravis and congenital myasthenic syndromes (CMS). In this study, we analyzed the effect of salbutamol in five patients with Dok-7 CMS.

METHODS

We studied 5 patients (2 male and 3 female), with a mean age of 27±11.06 years, who harbored c.1124_1127dupTGCC, p.G64R and/or p.S45L mutations in DOK7 gene. Salbutamol was given at a dose of 2mg three times daily (6 mg/day) to all patients. The response was assessed by QMG score at baseline, 3, 6, 9 and 12 months; ADL-MG score and 6 minute walk test at baseline and after 12 months during follow-up clinic visits. Side effect profile of salbutamol was also evaluated.

RESULTS

We noted an increasingly positive response as measured by the QMG score after 3 months of salbutamol treatment. Improvement in specific subcomponents of the QMG score such as leg outstretched in 45° supine was most marked. In ADL-MG scores and 6 minute walk test, comparison between baseline and after 12 months revealed a clear beneficial response. Salbutamol was well tolerated in all patients.

CONCLUSIONS

Salbutamol is an effective treatment in Dok-7 CMS. This study provides class IV evidence that salbutamol given at a dose 6 mg/day improves function as measured by the QMG score, ADL-MG score and 6 minute walk test.

Performance of individual items of the quantitative myasthenia gravis score

We evaluated the quantitative myasthenia gravis score to determine which items better discriminate among patients and are most responsive to treatment. Current scoring ranges were compared to updated normative data when appropriate. Data from a previous study of intravenous immunoglobulin versus placebo in myasthenia gravis were analyzed. Each item of the quantitative myasthenia gravis score was analyzed for distribution, responsiveness and inter-item correlations. Items on swallowing, speaking and vital capacity had marked floor effects as did grip strength based on current normative data. The timed measures were responsive to treatment but diplopia, vital capacity and grip strength were not. Ocular items were not correlated with bulbar and generalized items (p>0.05), suggesting multi-dimensionality. Contralateral arm and leg tests were highly correlated (r>0.9, p<0.001), indicating redundancy. In summary, we found that the bulbar items and grip strength did not perform well. Timed items from the Quantitative Myasthenia Gravis Score, representing fatigability, are responsive to change and we propose new ranges based on updated normative data.

Synaptic dysfunction in congenital myasthenic syndromes

Congenital myasthenic syndromes (CMS) are hereditary disorders of neuromuscular transmission characterized by fatigable muscle weakness. The number of cases recognized is increasing with improved diagnosis. To date we have identified over 300 different mutations present in over 350 unrelated kinships. The underlying genetic defects are diverse, involving a series of different genes with a variety of different phenotypes. The type of treatment and its effectiveness will depend on the underlying pathogenic mechanism. We aim to define the molecular mechanism for each mutation identified and feed this information back to the clinic as a basis to tailor patient treatment. Here, we describe some of the methods that can be used to define if a DNA sequence variant is pathogenic with reference to variants in DOK7. We highlight a new mechanism for disruption of AChR function, where a mutation in the AChR ɛ-subunit gene causes reduced ion channel conductance and discuss new methods for identifying gene mutations. The study of these disorders is proving highly informative for understanding the diverse molecular mechanisms that can underlie synaptic dysfunction.

Slow channel congenital myasthenic syndrome responsive to a combination of fluoxetine and salbutamol

INTRODUCTION

Slow channel congenital myasthenic syndrome is a dominant disorder characterized by prolonged acetylcholine receptor ion-channel activation.

METHODS

Molecular genetic techniques, electrophysiology, and binding studies in human embryonic kidney (HEK) 293 cells determined mutant function and expression levels. Patient response to treatment was measured by quantitative myasthenic gravis and Medical Research Council grade strength scores.

RESULTS

We report an unusual case due to heteroallelic mutations in CHRNE. The slow channel mutation, p.εS278del, is accompanied by a severe low-expression mutation, p.εR217L, on the second allele. Expression studies and cosegregation of p.εS278del with the disorder in the patient's offspring demonstrate robust expression of the p.εS278del mutation. The patient showed modest benefits from standard treatment with fluoxetine, but there was dramatic improvement when salbutamol was combined with fluoxetine.

CONCLUSIONS

This case suggests that salbutamol, which is beneficial in some other congenital myasthenic syndromes, might also be considered in addition to fluoxetine in slow channel syndrome.

Salbutamol benefits children with congenital myasthenic syndrome due to DOK7 mutations

Congenital myasthenic syndromes due to DOK7 mutations cause fatigable limb girdle weakness. Treatment with ephedrine improves muscle strength. Salbutamol, a β(2)-adrenergic receptor agonist with fewer side effects and more readily available, has been effective in adult and anecdotal childhood cases. This study reports the effects of salbutamol on motor function in childhood DOK7 congenital myasthenic syndrome. Nine children (age range 5.9-15.1years) were treated with oral salbutamol, 2-4mg TDS. The effect on timed tests of motor function, pre- and up to 28months post-treatment, was audited retrospectively. All 9 reported functional benefit within 1month, with progressive improvement to a plateau at 12-18months. Within the first month, all 3 non-ambulant children resumed walking with assistance. Although improvements were seen in some timed tests (timed 10m, arm raise time, 6min walk time) this did not fully reflect the observed functional benefits in daily living activities. No major side effects were reported. We conclude that oral salbutamol treatment significantly improves strength in children with DOK7 congenital myasthenic syndrome and is well tolerated. Outcome measures need to be refined further, both to accurately reflect functional abilities in children and to document progress and treatment response.

Neuromuscular junction acetylcholinesterase deficiency responsive to albuterol

Congenital myasthenic syndrome caused by endplate acetylcholinesterase deficiency constitutes a rare autosomal recessive disease. We describe a child with early-onset ptosis, complete ophthalmoplegia, facial and proximal muscle weakness, easy fatigability, a decremental electromyographic response, and a repetitive compound muscle action potential not improved by anti-acetylcholinesterase medication. Mutation analysis of the collagenic tail of endplate acetylcholinesterase (COLQ) that encodes the collagenic structural subunit of acetylcholinesterase revealed two canonic splice-site mutations: a previously identified IVS15 + 1G>A mutation and a novel IVS2 - 1G>A mutation. Treatment with albuterol resulted in progressive improvement of muscle strength, exercise tolerance, and ophthalmoplegia. Further studies are needed of the efficacy of albuterol in different types of congenital myasthenic syndrome and the physiologic basis of its beneficial effects.

Can a rare form of myasthenia gravis shed additional light on disease mechanisms?

A healthy 43-year-old physician developed gradually progressive and fluctuating fatigable muscle weakness involving ocular, limb, bulbar and respiratory muscles, with episodic acute respiratory failure, eventually necessitating intermittent non-invasive respiratory support (NIV). A mild short episode occurred 15 years earlier with complete resolution. Electromyography (EMG) studies and acetylcholine receptor (AchR) antibodies were repeatedly non-diagnostic. The diagnosis of myasthenia gravis (MG) was finally confirmed by direct measurement of diaphragmatic strength using magnetic nerve stimulation providing clear cut evidence of significant fatigable weakness and the demonstration of muscle-specific kinase (MuSK) serum antibodies using a novel cell-based assay. The cluster of several atypical features and lack of response to commonly used treatment modalities prompted a search for a unifying mechanism and better understanding of the underlying pathophysiology. Review of the literature suggested a possible impairment of excitation-contraction coupling with malfunction of a signaling protein downstream to the AchR, without an accompanying impairment of electrical transmission. This postulated mechanism, resulting in a disturbance of calcium signaling, explained the unusual features in this patient's illness and led to treatment with salbutamol and ephedrine and to significant symptomatic improvement not achieved by any other treatment.

The spectrum of mutations that underlie the neuromuscular junction synaptopathy in DOK7 congenital myasthenic syndrome

Congenital myasthenic syndromes (CMS) are a group of inherited diseases that affect synaptic transmission at the neuromuscular junction and result in fatiguable muscle weakness. A subgroup of CMS patients have a recessively inherited limb-girdle pattern of weakness caused by mutations in DOK7. DOK7 encodes DOK7, an adaptor protein that is expressed in the skeletal muscle and heart and that is essential for the development and maintenance of the neuromuscular junction. We have screened the DOK7 gene for mutations by polymerase chain reaction amplification and bi-directional sequencing of exonic and promoter regions and performed acetylcholine receptor (AChR) clustering assays and used exon trapping to determine the pathogenicity of detected variants. Approximately 18% of genetically diagnosed CMSs in the UK have mutations in DOK7, with mutations in this gene identified in more than 60 kinships to date. Thirty-four different pathogenic mutations were identified as well as 27 variants likely to be non-pathogenic. An exon 7 frameshift duplication c.1124_1127dupTGCC is commonly found in at least one allele. We analyse the effect of the common frameshift c.1124_1127dupTGCC and show that 10/11 suspected missense mutations have a deleterious effect on AChR clustering. We identify for the first time homozygous or compound heterozygous mutations that are localized 5' to exon 7. In addition, three silent variants in the N-terminal half of DOK7 are predicted to alter the splicing of the DOK7 RNA transcript. The DOK7 gene is highly polymorphic, and within these many variants, we define a spectrum of mutations that can underlie DOK7 CMS that will inform in managing this disorder.

Congenital myasthenic syndrome: a brief review

Congenital myasthenic syndromes comprise heterogeneous genetic diseases characterized by compromised neuromuscular transmission. Congenital myasthenic syndromes are classified as presynaptic, synaptic, or postsynaptic, depending on the primary defect's location within the neuromuscular junction. Presynaptic forms are the rarest, affecting an estimated 7-8% of patients; synaptic forms account for approximately 14-15% of patients; and the remaining 75-80% are attributable to postsynaptic defects. Clinical manifestations vary by congenital myasthenic syndrome subtype. Electrophysiologic, morphologic, and molecular descriptions of various forms of congenital myasthenic syndromes have led to an enhanced understanding of clinical manifestations and disease pathophysiology. Although congenital myasthenic syndromes are indicated by clinical manifestations, family history, electrophysiologic studies, and responses to acetylcholinesterase inhibitors, overlap in some presentations occurs. Therefore, genetic testing may be necessary to identify specific mutations in CHAT, COLQ, LAMB2, CHRNA, CHRNB, CHRND, CHRNE, CHRNG, RAPSN, DOK7, MUSK, AGRN, SCN4A, GFPT1, or PLEC1 genes. The identification of congenital myasthenic syndromes subtypes will prove important in the treatment of these patients. Different drugs may be beneficial, or should be avoided because they are ineffective or worsen some forms of congenital myasthenic syndromes. We explore the classification, clinical manifestations, electrophysiologic features, genetics, and treatment responses of each congenital myasthenic syndrome subtype.

Signaling and aging at the neuromuscular synapse: lessons learnt from neuromuscular diseases

The neuromuscular junction (NMJ) is a specialized synapse between motor neurons and skeletal muscle with a complex signaling network that assures highly reliable neuromuscular transmission. Diseases of the NMJ cause skeletal muscle fatigue and include inherited and acquired disorders that affect presynaptic, intrasynaptic or postsynaptic components. Moreover, fragmentation of the NMJ contributes to sarcopenia, the loss of muscle mass during aging. Studies from recent years indicate that the formation and stabilization of NMJs differs between various muscles and that this difference affects their response under pathological conditions. This review summarizes the most important mechanisms involved in the development, maintenance and dysfunction of the NMJ and it discusses their significance in myasthenic disorders and aging and as targets for possible future treatment of NMJ dysfunction.

Congenital myasthenic syndromes in 2012

Congenital myasthenic syndromes (CMS) represent a heterogeneous group of disorders in which the safety margin of neuromuscular transmission is compromised by one or more specific mechanisms. Clinical, electrophysiologic, and morphologic studies have paved the way for detecting CMS-related mutations in proteins residing in the nerve terminal, the synaptic basal lamina, or in the postsynaptic region of the motor endplate. The disease proteins identified to date include the acetylcholine receptor, acetylcholinesterase, choline acetyltransferase, rapsyn, and Na(v)1.4, muscle-specific kinase, agrin, β2-laminin, downstream of tyrosine kinase 7, and glutamine-fructose-6-phosphate transaminase 1. Analysis of electrophysiologic and biochemical properties of mutant proteins expressed in heterologous systems have contributed crucially to defining the molecular consequences of the observed mutations and have resulted in improved therapy of most CMS.

Motor neuron, nerve, and neuromuscular junction disease

PURPOSE OF REVIEW

The aim is to review the most relevant findings published during the last year concerning clinical, genetic, pathogenic, and therapeutic advances in motor neuron disease, neuropathies, and neuromuscular junction disorders.

RECENT FINDINGS

Studies on animal and cell models have improved the understanding of how mutated survival motor neuron protein in spinal muscular atrophy governs the pathogenetic processes. New phenotypes of SOD1 mutations have been described. Moreover, animal models enhanced the insight into the pathogenetic background of sporadic and familial amyotrophic lateral sclerosis. Novel treatment options for motor neuron disease have been described in humans and animal models. Considerable progress has been achieved also in elucidating the genetic background of many forms of inherited neuropathies and high clinical and genetic heterogeneity has been demonstrated. Mutations in MuSK and GFTP1 have been shown to cause new types of congenital myasthenic syndromes. A third type of autoantibodies (Lrp4) has been detected to cause myasthenia gravis.

SUMMARY

Advances in the clinical and genetic characterization of motor neuron diseases, neuropathies, and neuromuscular transmission defects have important implications on the fundamental understanding, diagnosis, and management of these disorders. Identification of crucial steps of the pathogenetic process may provide the basis for the development of novel therapeutic strategies.

Congenital myasthenic syndrome due to homozygous CHRNE mutations: report of patients in Arabia

We describe the clinical characteristics of 3 siblings from 1 family with congenital myasthenic syndrome due to homozygous mutations of the gene coding for the epsilon subunit of the acetylcholine receptor (CHRNE). Onset of symptoms occurred in the first few months of life with ptosis, restricted ocular motility, mild proximal weakness, and difficulty swallowing. Multiple hospital admissions were required due to recurrent pulmonary infections. There was no decremental conduction on repetitive nerve stimulation, but jitter was increased on single fiber electromyographic. Since early childhood, our patients have done well without pulmonary or bulbar symptoms and with partial improvement on pyridostigmine therapy. Response of ptosis to diagnostic ice pack test was striking. Although these siblings have a clinical history and examination findings typical of homozygous CHRNE mutations, the clinical presentation of congenital myasthenia subtypes is variable, and accurate genotyping is essential in choosing the appropriate treatment.

John Newsom-Davis: clinician-scientist and so much more

John Newsom-Davis was born in 1932 and died, aged 74, in 2007. After national service in the Royal Air Force, he read Natural Sciences at Cambridge. Following clinical studies at the Middlesex Hospital, he began research into respiratory neurophysiology with Tom Sears at the National Hospital, Queen Square, in London, and spent 1 year with Fred Plum at Cornell University in New York. After neurology specialist training at Queen Square, he became the director of the Batten Unit, continuing his interest in respiratory physiology. There he began to work on myasthenia gravis in collaboration with Ricardo Miledi at University College London and in 1978, after performing the first studies on plasma exchange in that disease, he established a myasthenia gravis research group at the Royal Free Hospital. There he investigated the role of the thymus in this disease and demonstrated an autoimmune basis for the Lambert Eaton myasthenic syndrome and 'seronegative' myasthenia. He was awarded the first Medical Research Council Clinical Research Professorship in 1979 but moved to Oxford in 1987 when he was elected Action Research Professor of Neurology. While at Oxford, he continued to run a very successful multidisciplinary group, researched further into the thymic abnormalities and cellular immunology of myasthenia, identified antibody-mediated mechanisms in acquired neuromyotonia, and began the molecular work that identified the genetic basis for many forms of congenital myasthenic syndrome. Meanwhile, he was also involved in university and college governance and contributed widely to the Medical Research Council, government committees, research charities and the Association of British Neurologists. Among many honours, he was elected Fellow of the Royal Society in 1991, appointed Commander of the British Empire in 1996 and made a Foreign Associate Member of the Institute of Medicine of the United States in 2001. Nearing and following retirement from Oxford, where he continued to see patients with myasthenia, he was the President of the Association of British Neurologists and Editor of Brain, and led a National Institutes of Health-funded international trial of thymectomy.

Beneficial effects of albuterol in congenital endplate acetylcholinesterase deficiency and Dok-7 myasthenia

INTRODUCTION

Congenital myasthenic syndromes (CMS) are disabling but treatable disorders. Anticholinesterase therapy is effective in most of them, but is contraindicated in endplate (EP) acetylcholinesterase (AChE) deficiency, the slow-channel syndrome, Dok-7 myasthenia, and β(2) -laminin deficiency, and is not useful in CMS due to defects in muscle-specific kinase (MuSK), agrin, and plectin. EP AChE, Dok-7, and β(2)-laminin deficiencies respond favorably to ephedrine, but ephedrine can no longer be prescribed in the USA.

METHODS

We used albuterol, another sympathomimetic agent, to treat 3 patients with EP AChE deficiency and 15 with Dok-7 myasthenia. Response to therapy was evaluated by a 9-point questionnaire pertaining to activities of daily life.

RESULTS

Comparison of the pre- and posttreatment responses indicated a beneficial response to albuterol (P < 0.001) in both patient groups. The adverse effects of therapy were like those of ephedrine.

CONCLUSION

Our observations should spur controlled, prospective clinical trials of albuterol in these as well as other CMS.

Genetic heterogeneity and pathophysiological mechanisms in congenital myasthenic syndromes

Congenital myasthenic syndromes (CMS) are a rare heterogeneous group of inherited neuromuscular disorders associated with distinctive clinical, electrophysiological, ultrastructural and genetic abnormalities. These genetic defects either impair neuromuscular transmission directly or result in secondary impairments, which eventually compromise the safety margin of neuromuscular transmission. In this report we will explore the significant progress made in understanding the molecular pathogenesis of CMS, which is important for both patients and clinicians in terms of reaching a definite diagnosis and selecting the most appropriate treatment.

Therapy update in nerve, neuromuscular junction and myopathic disorders

PURPOSE OF REVIEW

The objective of this review is to summarize recent advances in the treatment of various neuromuscular disorders including neuropathies, neuromuscular junction disorders, and myopathies.

RECENT FINDINGS

Immunotherapy with sophisticated agents for myasthenia gravis and inflammatory myopathies, neuroprotection with vitamin E for chemotherapy-induced neuropathy, and promising gene transfer and exon-skipping therapies for muscular dystrophy are among the most exciting recent developments in the treatment of neuromuscular disorders.

SUMMARY

In spite of significant advances, therapy in many neuromuscular diseases remains far from satisfactory. Better understanding of the underlying molecular and pathophysiologic processes for both hereditary and acquired disorders should lead to more refined and successful therapeutic approaches, reducing physical and other types of disability while posing fewer side effects.

Congenital stridor with feeding difficulty as a presenting symptom of Dok7 congenital myasthenic syndrome

OBJECTIVE

The congenital myasthenic syndromes (CMS) are a group of genetic disorders of neuromuscular transmission causing fatigable weakness. Symptoms may be present from birth, but diagnosis is often delayed for several years, notably in post-synaptic CMS due to mutations in the DOK7 gene. Recently, we noted a subgroup of children with CMS in whom congenital stridor and bilateral vocal cord palsy predated other symptoms. All had mutations in the DOK7 gene. The purpose of this study was to review our population of DOK7 CMS patients with congenital stridor and assess whether there were other phenotypic features which might raise suspicion of a diagnosis of CMS in the neonatal period, in the absence of limb weakness and ptosis and prompt earlier referral for neurophysiological investigation, genetic diagnosis and appropriate treatment.

METHODS

A retrospective case review of 11 DOK7 CMS patients at a tertiary referral centre.

RESULTS

Six patients were identified with DOK7 mutations and congenital stridor, four requiring intubation soon after birth. Four patients had a diagnosis of bilateral vocal cord palsy and three required tracheostomy, successfully decannulated in one after 3 years. All six patients had difficulty with feeding, with weak suck and swallow necessitating nasogastric feeding in five, two of whom required gastrostomy. Despite all six children having had neonatal symptoms, the mean age at CMS diagnosis was 5 years and 9 months.

CONCLUSION

CMS, particularly caused by mutations in the DOK7 gene, is a rare but treatable cause of congenital stridor in the neonate. A combination of congenital stridor, especially with an apparently idiopathic bilateral vocal cord palsy and weak suck and swallow should alert the clinician to the possibility of CMS and prompt early referral for neurophysiology and genetic investigations. Confirmation of a CMS diagnosis enables treatment to be initiated, informed management of the VCP and anticipation of myasthenic symptoms, particularly life-threatening respiratory decompensation. Treatment may allow early decannulation or possible avoidance of tracheostomy. At least 12 genes are known to cause CMS; the presence of congenital stridor may help target genetic diagnosis.