DOK7 congenital myasthenic syndrome in childhood: Early diagnostic clues in 23 children

Homozygosity of a Founder Variant c.1508dupC in DOK7 Causes Congenital Myasthenia With Variable Severity

Background and Objectives

Description of 15 patients with the same variant in DOK7 causing congenital myasthenic syndrome (CMS).

Methods

Nine adult and 6 pediatric patients were studied with molecular genetic and clinical investigations.

Results

All patients were identified with the c.1508dupC variant in DOK7, of whom 13 were homozygous and 2 patients compound heterozygous. Only 2 patients had limb girdle phenotype, while all adult patients also had ptosis, ophthalmoplegia, facial weakness, as well as inspiratory stridor. Pediatric patients had severe respiratory insufficiency and feeding difficulties at birth.

Discussion

The disease severity in our patients varied extensively from ventilator or wheelchair dependence to mild facial weakness, ptosis, and ophthalmoparesis. Most of the patients had normal transmission in conventional 3 Hz stimulation electrophysiologic studies, making the diagnosis of CMS challenging. Our cohort of adult and pediatric patients expands the phenotype of DOK7 CMS and shows the importance of correct and early diagnosis.

When Breathing Becomes a Challenge: A Case of Congenital Myasthenia Gravis in an Indian Neonate With a DOK-7 Gene Mutation

A rare neuromuscular condition known as congenital myasthenia gravis (CMG) affects some people from birth or very soon after. It results in fatigue and muscle weakness because of genetic abnormalities that interfere with the neuromuscular junction's ability to function, where the nerves and muscles connect. Even among those who have the same genetic mutation, the severity of CMG symptoms might differ considerably. The most typical signs of CMG include eyelid drooping, breathing issues, muscle weakness and weariness, and difficulties swallowing. Clinical examinations, neurophysiologic tests, and genetic analyses are frequently combined to make the diagnosis of CMG. Although there is no known treatment for CMG, many patients may control their symptoms and lead relatively normal lives with the right care. A newborn with CMG due to a DOK-7 gene mutation is described in this article, along with its very early onset. The DOK-7 mutation is a rare variant in the Indian population that causes CMG and usually manifests as 'limb girdle' weakness. However, due to muscle weakness, the neonate in this case developed severe respiratory distress and later died despite rigorous life-saving measures.

Congenital or Early Developing Neuromuscular Diseases Affecting Feeding, Swallowing and Speech – A Review of the Literature from January 1998 to August 2021

Background:

The knowledge about the impact of oral motor impairment in neuromuscular diseases (NMDs) is limited but increasing.

Objective:

The aim of this review was to collect and compile knowledge on how muscle weakness in congenital or early developing NMDs directly or indirectly affects feeding, swallowing, speech and saliva control.

Methods:

A literature search was performed in PubMed from January 1, 1998, to August 31, 2021. The keywords “feeding”, “dysphagia”, “swallowing”, “dysarthria”, “speech”, “drooling” and “sialorrhea” were used in combination with “paediatric neuromuscular disease” or specific diagnoses.

Results:

Sixty-five studies were selected for the review, 33 focused on feeding and swallowing, 11 on speech, four on a combination of feeding, swallowing, saliva control or speech and 17 general descriptions. Most of the studies reported on patients with a disorder affecting muscles. These studies show that muscle weakness and impaired motility affecting the muscles innervated by the cranial nerves may influence feeding, swallowing, and speech, and that respiratory function, general health and neurodevelopmental delay also influence these functions. Feeding impairment and breathing difficulties are common in NMDs. Lifesaving interventions such as tube feeding and ventilatory support are common in severe cases.

Conclusions:

Feeding impairment, dysphagia and dysarthria are prevalent in NMDs with congenital or early age of onset. Feeding and swallowing has been studied more than speech and saliva control. More children with NMD survive thanks to new treatment options and it is therefore urgent to follow up how these therapies may impact the development of feeding, swallowing, and speech.

Single fiber electromyography and measuring jitter with concentric needle electrodes

This monograph contains descriptions of the single fiber electromyography (SFEMG) method and of the more recently implemented method of recording jitter with concentric needle electrodes (CNEs). SFEMG records action potentials from single muscle fibers (SFAPs), which permits measuring fiber density (FD), a sensitive measure of reinnervation, and jitter, a sensitive measure of abnormal neuromuscular transmission (NMT). With voluntary activation, jitter is measured between two SFAPs with acceptable amplitude and rise time. With activation by axon stimulation, jitter is measured between the stimulus and individual SFAPs. Pitfalls due to unstable triggers and inconstant firing rates during voluntary activation and subliminal stimulation during axon stimulation should be identified and avoided. In CNE recordings, spikes with shoulders or rising phases that are not parallel are produced by summation of SFAPS; these should be excluded and reference values for CNE jitter should be used. CNE and SFEMG have similar and very high sensitivity in detecting increased jitter, as in myasthenia gravis and other myasthenic conditions. However, jitter is also seen in ongoing reinnervation and some myopathic conditions. With SFEMG, these can be identified by increased FD; however, FD cannot be measured with CNE, and conventional electromyography should be performed in muscles with increased jitter to detect neurogenic or myogenic abnormalities. Jitter is abnormal after injections of botulinum toxin, even in muscles remote from the injection site, and can persist for 6 mo or more. This can complicate the detection or exclusion of abnormal NMT.

Single fiber EMG and measuring jitter with concentric needle electrodes

This monograph contains descriptions of the single-fiber electromyography (SFEMG) method and of the more recently implemented method of recording jitter with concentric needle electrodes (CNE). SFEMG records action potentials from single muscle fibers (SFAPs), which permits measuring fiber density (FD), a sensitive measure of reinnervation, and jitter, a sensitive measure of abnormal neuromuscular transmission (NMT). With voluntary activation, jitter is measured between two SFAPs with acceptable amplitude and rise time. With activation by axon stimulation, jitter is measured between the stimulus and individual SFAPs. Pitfalls due to unstable triggers and inconstant firing rates during voluntary activation and subliminal stimulation during axon stimulation should be identified and avoided. In CNE recordings, spikes with shoulders or rising phases that are not parallel are produced by summation of SFAPS; these should be excluded and reference values for CNE jitter should be used. CNE and SFEMG have similar and very high sensitivity in detecting increased jitter, as in myasthenia gravis and other myasthenic conditions. However, jitter is also seen in ongoing reinnervation and some myopathic conditions. With SFEMG, these can be identified by increased FD; however, FD cannot be measured with CNE, and conventional EMG should be performed in muscles with increased jitter to detect neurogenic or myogenic abnormalities. Jitter is abnormal after injections of botulinum toxin, even in muscles remote from the injection site, and can persist for 6 mo or more. This can complicate the detection or exclusion of abnormal NMT.

A novel DOK7 mutation causing congenital myasthenic syndrome with limb-girdle weakness: case series of three family members

Congenital myasthenia syndrome (CMS) is a group of heterogeneous diseases affecting the neuromuscular endplate. CMS has a considerably different phenotypic presentations, with the onset time ranging from early infancy to late adulthood. Here, we report a case of a CMS due to a new DOK7 mutation in a 28-year-old man and two of his sisters, who have a pure limb-girdle weakness. DOK7 CMS has a varying presentation. Typically, the onset occurs in childhood with ptosis, bulbar symptoms, difficulty walking, weakness, and gait abnormality. This case sheds light on a novel DOK7 gene mutation with a unique presentation of CMS and provides insight into its unique phenotypic presentation.

Congenital myasthenic syndrome in China: genetic and myopathological characterization

OBJECTIVE

We aimed to summarize the clinical, genetic, and myopathological features of a cohort of Chinese patients with congenital myasthenic syndrome, and follow up on therapeutic outcomes.

METHODS

The clinical spectrum, mutational frequency of genes, and pathological diagnostic clues of various subtypes of patients with congenital myasthenic syndrome were summarized. Therapeutic effects were followed up.

RESULTS

Thirty-five patients from 29 families were recruited. Ten genes were identified: GFPT1 (27.6%), AGRN (17.2%), CHRNE (17.2%), COLQ (13.8%), GMPPB (6.9%), CHAT, CHRNA1, DOK7, COG7, and SLC25A1 (3.4% each, respectively). Sole limb-girdle weakness was found in patients with AGRN (1/8) and GFPT1 (7/8) mutations, whereas distal weakness was all observed in patients with AGRN (6/8) mutations. Tubular aggregates were only found in patients with GFPT1 mutations (5/6). The patients with GMPPB mutations (2/2) had decreased alpha-dystroglycan. Acetylcholinesterase inhibitor therapy resulted in no response or worsened symptoms in patients with COLQ mutations, a diverse response in patients with AGRN mutations, and a good response in patients with other subtypes. Albuterol therapy was effective or harmless in most subtypes. Therapy effects became attenuated with long-term use in patients with COLQ or AGRN mutations.

INTERPRETATION

The genetic distribution of congenital myasthenic syndrome in China is distinct from that of other ethnic origins. The appearance of distal weakness, selective limb-girdle myasthenic syndrome, tubular aggregates, and decreased alpha-dystroglycan were indicative of the specific subtypes. Based on the follow-up findings, we suggest cautious evaluation of the long-term efficacy of therapeutic agents in congenital myasthenic syndrome.

Electrophysiological study of neuromuscular junction in congenital myasthenic syndromes, congenital myopathies, and chronic progressive external ophthalmoplegia

This study was designed to analyze the sensitivity, specificity, and accuracy of jitter parameters combined with repetitive nerve stimulation (RNS) in congenital myasthenic syndrome (CMS), chronic progressive external ophthalmoplegia (CPEO), and congenital myopathies (CM). Jitter was obtained with a concentric needle electrode during voluntary activation of the Orbicularis Oculi muscle in CMS (n = 21), CPEO (n = 20), and CM (n = 18) patients and in controls (n = 14). RNS (3 Hz) was performed in six different muscles for all patients (Abductor Digiti Minimi, Tibialis Anterior, upper Trapezius, Deltoideus, Orbicularis Oculi, and Nasalis). RNS was abnormal in 90.5% of CMS patients and in only one CM patient. Jitter was abnormal in 95.2% of CMS, 20% of CPEO, and 11.1% of CM patients. No patient with CPEO or CM presented a mean jitter higher than 53.6 µs or more than 30% abnormal individual jitter (> 45 µs). No patient with CPEO or CM and mild abnormal jitter values presented an abnormal decrement. Jitter and RNS assessment are valuable tools for diagnosing neuromuscular transmission abnormalities in CMS patients. A mean jitter value above 53.6 µs or the presence of more than 30% abnormal individual jitter (> 45 µs) strongly suggests CMS compared with CPEO and CM.

Trouble at the junction: When myopathy and myasthenia overlap

Although myopathies and neuromuscular junction disorders are typically distinct, their coexistence has been reported in several inherited and acquired conditions. Affected individuals have variable clinical phenotypes but typically display both a decrement on repetitive nerve stimulation and myopathic findings on muscle biopsy. Inherited causes include myopathies related to mutations in BIN1, DES, DNM2, GMPPB, MTM1, or PLEC and congenital myasthenic syndromes due to mutations in ALG2, ALG14, COL13A1, DOK7, DPAGT1, or GFPT1. Additionally, a decrement due to muscle fiber inexcitability is observed in certain myotonic disorders. The identification of a defect of neuromuscular transmission in an inherited myopathy may assist in establishing a molecular diagnosis and in selecting patients who would benefit from pharmacological correction of this defect. Acquired cases meanwhile stem from the co-occurrence of myasthenia gravis or Lambert-Eaton myasthenic syndrome with an immune-mediated myopathy, which may be due to paraneoplastic disorders or exposure to immune checkpoint inhibitors.

Phenotypic Differences in 2 Unrelated Cases Carrying Identical DOK7 Mutations

INTRODUCTION

Mutations in the Dok-7 gene (DOK7) underlie a congenital myasthenic syndrome (CMS) with a characteristic limb-girdle (LG) pattern of muscle weakness. Multiple clinical findings and a wide clinical heterogeneity have been identified in this form of CMS.

METHODS

We describe here 2 unrelated adult patients who presented with a LG CMS, caused by 2 compound heterozygous pathogenic sequence variants in DOK7: c.1124_1127dupTGCC (P.Ala378Serfs*30) and c.480C> A (p.Tyr160*).

RESULTS

Although both patients presented with severe proximal weakness consistent with LG myasthenia, one of the patients presented with additional distal muscle involvement in the lower extremities. By contrast, the other patient had severe bulbar and respiratory deficit requiring gastric tube feeding and mechanical ventilatory support for most parts of the day.

DISCUSSION

These 2 cases illustrate the lack of phenotype-genotype correlation and the absence of geographic, genetic, and ethnic association in cases of LG CMS caused by DOK7 mutations.

Isolated vocal cord paralysis in two siblings with compound heterozygous variants in MUSK: Expanding the phenotypic spectrum

The congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders caused by perturbations in signal transduction at the neuromuscular junction. Defects in muscle, skeletal, receptor tyrosine kinase (MuSK) cause two distinct phenotypes: fetal akinesia with multiple congenital anomalies (Fetal akinesia deformation sequence [MIM:208150]) and early onset congenital myasthenia (myasthenic syndrome, congenital, 9, associated with acetylcholine receptor deficiency [MIM:616325]). Myasthenia due to MuSK deficiency has variable clinical features, ranging from a milder presentation of isolated late-onset proximal muscle weakness; to a severe presentation of prenatal-onset diffuse weakness, ophthalmoplegia, respiratory failure, and vocal cord paralysis (VCP). Here, we propose to expand the phenotypic spectrum for MuSK deficiency to include isolated VCP with the absence of other classical myasthenic symptoms. We evaluated two brothers who presented in the neonatal period with respiratory failure secondary to isolated VCP. Research-based exome sequencing revealed biallelic likely pathogenic variants in MUSK (MIM:601296). Both children had normal gross motor and fine motor development. One brother had speech delay, likely due to a combination of tracheostomy status and ankyloglossia. This case report suggests that CMS should be on the differential diagnosis for familial recurrence of VCP.

Congenital myasthenic syndromes in adult neurology clinic: A long road to diagnosis and therapy

OBJECTIVE

To investigate the diagnostic challenges of congenital myasthenic syndromes (CMS) in adult neuromuscular practice.

METHODS

We searched the Mayo Clinic database for patients with CMS diagnosed in adulthood in the neuromuscular clinic between 2000 and 2016. Clinical, laboratory, and electrodiagnostic data were reviewed.

RESULTS

We identified 34 patients with CMS, 30 of whom had a molecular diagnosis (14 DOK7, 6 RAPSN, 2 LRP4, 2 COLQ, 2 slow-channel syndrome, 1 primary acetylcholine receptor deficiency, 1 AGRN, 1 GFPT1, and 1 SCN4A). Ophthalmoparesis was often mild and present in 13 patients. Predominant limb-girdle weakness occurred in 19 patients. Two patients had only ptosis. Age at onset ranged from birth to 39 years (median 5 years). The median time from onset to diagnosis was 26 years (range 4-56 years). Thirteen patients had affected family members. Fatigable weakness was present when examined. Creatine kinase was elevated in 4 of 23 patients (range 1.2-4.2 times the upper limit of normal). Repetitive nerve stimulation revealed a decrement in 30 patients. Thirty-two patients were previously misdiagnosed with seronegative myasthenia gravis (n = 16), muscle diseases (n = 15), weakness of undetermined cause (n = 8), and others (n = 4). Fifteen patients received immunotherapy or thymectomy without benefits. Fourteen of the 25 patients receiving pyridostigmine did not improve or worsen.

CONCLUSION

Misdiagnosis occurred in 94% of the adult patients with CMS and causes a median diagnostic delay of nearly 3 decades from symptom onset. Seronegative myasthenia gravis and muscle diseases were the 2 most common misdiagnoses, which led to treatment delay and unnecessary exposure to immunotherapy, thymectomy, or muscle biopsy.

Familial impairment of vocal cord mobility in childhood with clubfoot

We report on a family with three siblings, male and female, affected by congenital bilateral limitation of vocal cord abduction, with the additional finding of clubfeet in two. The paternal family history suggests an autosomal dominant inheritance. The siblings and father also have mild craniofacial features, which may be an expression of variability or may be unrelated. The association between congenital vocal cord paralysis and clubfeet has been reported with additional major features or in the context of Charcot-Marie-Tooth disease. However, the two in isolation have only been reported in one other family previously. Genomic analyses of the family, including chromosomal microarray and exome sequencing, showed neither a likely pathogenic variant in a known disease gene nor a compelling candidate gene variant. We propose that the association of these two findings constitutes a novel recognizable phenotype, for which a genetic cause remains undetermined.

Clinical and research strategies for limb-girdle congenital myasthenic syndromes

Congenital myasthenic syndromes (CMS) are a group of rare disorders that cause fatigable muscle weakness due to defective signal transmission at the neuromuscular junction, a specialized synapse between peripheral motor neurons and their target muscle fibers. There are now over 30 causative genes that have been reported for CMS. Of these, there are 10 that are associated with a limb-girdle pattern of muscle weakness and are thus classed as LG-CMS. Next-generation sequencing and advanced methods of data sharing are likely to uncover further genes that are associated with similar clinical phenotypes, contributing to better diagnosis and effective treatment of LG-CMS patients. This review highlights clinical and pathological hallmarks of LG-CMS in relation to the underlying genetic defects and pathways. Tailored animal and cell models are essential to elucidate the exact function and pathomechanisms at the neuromuscular synapse that underlie LG-CMS. The integration of genomics and proteomics data derived from these models and patients reveals new and often unexpected insights that are relevant beyond the rare genetic disorder of LG-CMS and may extend to the functioning of mammalian synapses in health and disease more generally.

Congenital Myasthenic Syndrome due to DOK7 mutations in a family from Chile

Congenital myasthenic syndromes (CMS) are neuromuscular transmission disorders caused by mutations in genes encoding neuromuscular junction proteins. A 61-year-old female and her older sister showed bilateral ptosis, facial and proximal limb weakness, and scoliosis since childhood. Another female sibling had milder signs, while other family members were asymptomatic. Facial nerve repetitive stimulation in the proband showed decrement of muscle responses. Single fiber EMG revealed increased jitter and blocking. Muscle biopsy showed type 2-fiber atrophy, without tubular aggregates. Mutational analysis in the three affected siblings revealed two compound heterozygous mutations in DOK7: c.1457delC, that predicts p.Pro486Argfs*13 and truncates the protein C-terminal domain, and c.473G>A, that predicts p.Arg158Gln and disruption of the dok7-MuSK interaction in the phosphotyrosine binding (PTB) domain. Unaffected family members carried only one or neither mutation.

Discussion

Two of the affected sisters showed marked improvement with salbutamol treatment, which illustrates the benefits of a correct diagnosis and treatment of DOK7-CMS.

Clinical features of the myasthenic syndrome arising from mutations in GMPPB

BACKGROUND

Congenital myasthenic syndrome (CMS) due to mutations in GMPPB has recently been reported confirming the importance of glycosylation for the integrity of neuromuscular transmission.

METHODS

Review of case notes of patients with mutations in GMPPB to identify the associated clinical, neurophysiological, pathological and laboratory features. In addition, serum creatine kinase (CK) levels within the Oxford CMS cohort were retrospectively analysed to assess its usefulness in the differential diagnosis of this new entity.

RESULTS

All patients had prominent limb-girdle weakness with minimal or absent craniobulbar manifestations. Presentation was delayed beyond infancy with proximal muscle weakness and most patients recall poor performance in sports during childhood. Neurophysiology showed abnormal neuromuscular transmission only in the affected muscles and myopathic changes. Muscle biopsy showed dystrophic features and reduced α-dystroglycan glycosylation. In addition, myopathic changes were present on muscle MRI. CK was significantly increased in serum compared to other CMS subtypes. Patients were responsive to pyridostigimine alone or combined with 3,4-diaminopyridine and/or salbutamol.

CONCLUSIONS

Patients with GMPPB-CMS have phenotypic features aligned with CMS subtypes harbouring mutations within the early stages of the glycosylation pathway. Additional features shared with the dystroglycanopathies include myopathic features, raised CK levels and variable mild cognitive delay. This syndrome underlines that CMS can occur in the absence of classic myasthenic manifestations such as ptosis and ophthalmoplegia or facial weakness, and links myasthenic disorders with dystroglycanopathies. This report should facilitate the recognition of this disorder, which is likely to be underdiagnosed and can benefit from symptomatic treatment.

Muscle magnetic resonance imaging in congenital myasthenic syndromes

Introduction

In this study we investigated muscle magnetic resonance imaging in congenital myasthenic syndromes (CMS).

Methods

Twenty‐six patients with 9 CMS subtypes and 10 controls were imaged. T1‐weighted (T1w) and short‐tau inversion recovery (STIR) 3‐Tesla MRI images obtained at thigh and calf levels were scored for severity.

Results

Overall mean the T1w score was increased in GFPT1 and DPAGT1 CMS. T1w scans of the AChR‐deficiency, COLQ, and CHAT subjects were indistinguishable from controls. STIR images from CMS patients did not differ significantly from those of controls. Mean T1w score correlated with age in the CMS cohort.

Conclusions

MRI appearances ranged from normal to marked abnormality. T1w images seem to be especially abnormal in some CMS caused by mutations of proteins involved in the glycosylation pathway. A non‐selective pattern of fat infiltration or a normal‐appearing scan in the setting of significant clinical weakness should suggest CMS as a potential diagnosis. Muscle MRI could play a role in differentiating CMS subtypes. Muscle Nerve54: 211–219, 2016

Effective Treatment With Albuterol in DOK7 Congenital Myasthenic Syndrome in Children

BACKGROUND

Congenital myasthenic syndromes consist of rare disorders resulting from mutations in genes encoding for presynaptic, synaptic, and postsynaptic proteins that are involved in the signal transmission of the neuromuscular junction. They are characterized by fatigable weakness of the skeletal muscles with symptom onset from birth to early childhood. DOK7 (downstream of tyrosine kinase 7) congenital myasthenic syndrome was previously treated successfully with ephedrine and salbutamol; however, both are unavailable in the United States.

METHODS

Case report of a child with muscle weakness.

RESULTS

This report describes a boy who presented only with progressive limb-girdle muscle weakness since age 2 years. The muscle biopsy with extensive studies revealed no obvious etiologies. His muscle weakness rapidly worsened, requiring a wheelchair for daily activities. Expanded neuromuscular gene panel promptly led to the diagnosis of DOK7 congenital myasthenic syndrome, and his muscle strength dramatically and persistently improved in four weeks with albuterol treatment, allowing him to walk independently. In a brief literature review, 15 patients (five treated between ages 5 and 17 years) from the Mayo Clinic with DOK7 mutations were also successfully treated with albuterol.

CONCLUSION

DOK7 congenital myasthenic syndrome often presents with limb-girdle muscle weakness, which can become progressive without proper treatment. If muscle biopsy reveals no obvious etiology, an expanded neuromuscular gene panel may lead to a specific diagnosis of congenital myasthenic syndrome such as those due to DOK7 mutation. Albuterol is often used to treat bronchial asthma; however, it can also dramatically and persistently improve the muscle strength of DOK7 congenital myasthenic syndrome.

Familial congenital bilateral vocal fold paralysis: a novel gene translocation

OBJECTIVES

True vocal fold (TVF) paralysis is a common cause of neonatal stridor and airway obstruction, though bilateral TVF paralysis is seen less frequently. Rare cases of familial congenital TVF paralysis have been described with implied genetic origin, but few genetic abnormalities have been discovered to date. The purpose of this study is to describe a novel chromosomal translocation responsible for congenital bilateral TVF immobility.

METHODS

The charts of three patients were retrospectively reviewed: a 35 year-old woman and her two children. The mother had bilateral TVF paralysis at birth requiring tracheotomy. Her oldest child had a similar presentation at birth and also required tracheotomy, while the younger child had laryngomalacia without TVF paralysis. Standard karyotype analysis was done using samples from all three patients and the parents of the mother, to assess whether a chromosomal abnormality was responsible.

RESULTS

Karyotype analysis revealed the same balanced translocation between chromosomes 5 and 14, t(5;14) (p15.3, q11.2) in the mother and her two daughters. No other genetic abnormalities were identified. Neither maternal grandparent had the translocation, which appeared to be a spontaneous mutation in the mother with autosomal dominant inheritance and variable penetrance.

CONCLUSIONS

A novel chromosomal translocation was identified that appears to be responsible for familial congenital bilateral TVF paralysis. While there are other reports of genetic abnormalities responsible for this condition, we believe this is the first describing this particular translocation.

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.

Congenital myasthenic syndrome caused by mutations in DPAGT

Congenital myasthenic syndromes with prominent limb girdle involvement are an important differential diagnosis for congenital myopathies because of the therapeutic considerations. We present a case where accurate diagnosis was delayed for many years. Fluctuations of weakness were misinterpreted as effects of alternative treatments. Weakness was generalised, most prominently in the arms. Fatigability was more prominent in less affected muscles revealed by a positive Simpson test. Stimulation single fibre electromyography confirmed the suspected neuromuscular transmission defect. The marked response to pyridostigmine and cognitive impairment pointed to a myasthenic syndrome due to impaired glycosylation. Two mutations in trans were found in DPAGT1, the gene coding for dolichyl-phosphate N-acetylglucosaminephosphotransferase, one novel, the other previously reported in a rare form of congenital disorder of glycosylation. Gene expression studies revealed that both mutations reduce DPAGT1 expression. Phenotypic features not previously described for DPAGT1 CMS included restricted ocular abduction and long finger flexor contractures.

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.