Congenital Myasthenic Syndromes Patients Research Articles

Unique genotypic pattern in Indian DPAGT1 congenital myasthenic syndrome patients with two likely founder mutations

Unique genotypic pattern in Indian DPAGT1 congenital myasthenic syndrome patients with two likely founder mutations

Congenital myasthenic syndromes: a retrospective natural history study of respiratory outcomes in a single centre.

Respiratory problems are a major cause of morbidity and mortality in patients with congenital myasthenic syndromes, a rare heterogeneous group of neuromuscular disorders caused by genetic defects impacting the structure and function of the neuromuscular junction. Recurrent, life-threatening episodic apnoea in early infancy and childhood and progressive respiratory failure requiring ventilation are features of certain genotypes of congenital myasthenic syndromes. Robb et al. published empirical guidance on respiratory management of the congenital myasthenic syndromes, but other than this workshop report, there are little published longitudinal natural history data on respiratory outcomes of these disorders. We report a retrospective, single-centre study on respiratory outcomes in a cohort of 40 well characterized genetically confirmed cases of congenital myasthenic syndromes, including 10 distinct subtypes (DOK7, COLQ, RAPSN, CHAT, CHRNA1, CHRNG, COL13A1, CHRNE, CHRNE fast channel syndrome and CHRNA1 slow channel syndrome), with many followed up over 20 years in our centre. A quantitative and longitudinal analysis of key spirometry and sleep study parameters, as well as a description of historical hospital admissions for respiratory decompensation, provides a snapshot of the respiratory trajectory of congenital myasthenic syndrome patients based on genotype.

Clinical and genetic characterisation of a large Indian congenital myasthenic syndrome cohort.

Congenital myasthenic syndromes (CMS) are a rare group of inherited disorders caused by gene defects associated with the neuromuscular junction and potentially treatable with commonly available medications such as acetylcholinesterase inhibitors and β2 adrenergic receptor agonists. In this study, we identified and genetically characterized the largest cohort of CMS patients from India to date. Genetic testing of clinically suspected patients evaluated in a South Indian hospital during the period 2014-19 was carried out by standard diagnostic gene panel testing or using a two-step method that included hotspot screening followed by whole-exome sequencing. In total, 156 genetically diagnosed patients (141 families) were characterized and the mutational spectrum and genotype-phenotype correlation described. Overall, 87 males and 69 females were evaluated, with the age of onset ranging from congenital to fourth decade (mean 6.6 ± 9.8 years). The mean age at diagnosis was 19 ± 12.8 (1-56 years), with a mean diagnostic delay of 12.5 ± 9.9 (0-49 years). Disease-causing variants in 17 CMS-associated genes were identified in 132 families (93.6%), while in nine families (6.4%), variants in genes not associated with CMS were found. Overall, postsynaptic defects were most common (62.4%), followed by glycosylation defects (21.3%), synaptic basal lamina genes (4.3%) and presynaptic defects (2.8%). Other genes found to cause neuromuscular junction defects (DES, TEFM) in our cohort accounted for 2.8%. Among the individual CMS genes, the most commonly affected gene was CHRNE (39.4%), followed by DOK7 (14.4%), DPAGT1 (9.8%), GFPT1 (7.6%), MUSK (6.1%), GMPPB (5.3%) and COLQ (4.5%). We identified 22 recurrent variants in this study, out of which eight were found to be geographically specific to the Indian subcontinent. Apart from the known common CHRNE variants p.E443Kfs*64 (11.4%) and DOK7 p.A378Sfs*30 (9.3%), we identified seven novel recurrent variants specific to this cohort, including DPAGT1 p.T380I and DES c.1023+5G>A, for which founder haplotypes are suspected. This study highlights the geographic differences in the frequencies of various causative CMS genes and underlines the increasing significance of glycosylation genes (DPAGT1, GFPT1 and GMPPB) as a cause of neuromuscular junction defects. Myopathy and muscular dystrophy genes such as GMPPB and DES, presenting as gradually progressive limb girdle CMS, expand the phenotypic spectrum. The novel genes MACF1 and TEFM identified in this cohort add to the expanding list of genes with new mechanisms causing neuromuscular junction defects.

Congenital myasthenic syndromes (CMS) a rare cause of uncommon fatigue

Introduction and purpose:
 Muscle weakness in newborns, infants and young children can be caused by disorders of the neuromuscular junction (NMJ). Congenital myasthenic syndromes (CMS) are a group of rare genetic diseases whose symptoms resemble the clinical picture of autoimmune myasthenia gravis. There are many mutations that can disrupt the neuromuscular transmission leading to pathology. The diagnosis of CMS is based on genetic testing. The aim of this study is to draw clinicians' attention to the symptoms and present current forms of CMS diagnosis and management.
 State of knowledge:
 An increasing number of genetic changes are associated with CMS pathology. They are divided, depending on the location in the NMJ of the encoded protein, into presynaptic, synaptic and postsynaptic. The most common disorder is the mutation of CHRNE, which is responsible for the expression of one of the subunits in the structure of the acetylcholine receptor. Regardless of the type of disease, the characteristic symptom is uncommon fatigue of skeletal muscles. It may present as ptosis of one or both eyelids or gait disturbance. The interview, laboratory tests and EMG are helpful in the diagnosis, but genetic tests play a key role. They can target specific mutations or cover the entire genome comprehensively. Currently used drugs alleviate the course of CMS by increasing the release of acetylcholine or increasing the concentration of acetylcholine in the synaptic cleft.
 Conclusion:
 Because of its rarity and variability, many CMS patients may be misdiagnosed. It is important to implement extensive genetic diagnostics and early implementation of treatment. There is a need for long-term studies of CMS cases and implementation of therapies targeted at specific mutations.

VP.41 Congenital myasthenic syndrome: natural history of an Italian cohort of patients

Congenital myasthenic syndromes (CMS) are genetic diseases characterized by impairment of the structure or function of the neuromuscular junction. CMS natural history has been poorly investigated and has not been clarified yet. Aim of this study is to longitudinally assess the disease course of CMS in an Italian cohort of patients. We included genetically defined CMS, followed in three Italian neuromuscular centres. Patients were evaluated at baseline and then once per year, with a minimum follow-up of 2 years. Neurological examination included the Myasthenia Gravis–specific Activities of Daily Living scale (MG-ADL), the MG-composite scale (MGC), time to get up from the floor and from a chair, upper and lower limbs fatigability (Mingazzini I and II manoeuvres). A total of 40 patients, including 16 males and 24 females, were enrolled. The most common mutated gene was CHRNE (n=17 pts), followed by DOK7 (n=5 pts) and GFPT1 (n= 4 pts). Mean age at first evaluation was 39.2 ± 15.2 years (range=10-71) and mean follow-up period was 2.1 ± 0.5 years (range=2-3). Mean MG-ADL and MGC scores at baseline were 5.3 ± 3.6 and 10.5 ± 6.8, respectively, with a significant improvement during the follow-up period (p-value=0.0000 for MG-ADL; p-value=0.0037 for MGC) mainly related to treatment modifications. Good concordance was found between MG-ADL and MGC across the 2-year period. Conversely, no significant changes of upper and lower limb fatigability or timed tests were reported between baseline and following visits. Our preliminary data suggest no overall disease progression over a 2-year period in CMS patients.

Two Congenital Myasthenic Syndrome Patients Due to Mutations in <i>COLQ</i> Gene and the Consequence Protein Defect Prediction

Two Congenital Myasthenic Syndrome Patients Due to Mutations in <i>COLQ</i> Gene and the Consequence Protein Defect Prediction

Congenital myasthenic syndrome: Correlation between clinical features and molecular diagnosis.

To present phenotype features of a large cohort of congenital myasthenic syndromes (CMS) and correlate them with their molecular diagnosis. Suspected CMS patients were divided into three groups: group A (limb, bulbar or axial weakness, with or without ocular impairment, and all the following: clinical fatigability, electrophysiology compatible with neuromuscular junction involvement and anticholinesterase agents response), group B (limb, bulbar or axial weakness, with or without ocular impairment, and at least one of additional characteristics noted in group A) and group C (pure ocular syndrome). Individual clinical findings and the clinical groups were compared between the group with a confirmed molecular diagnosis of CMS and the group without molecular diagnosis or with a non-CMS molecular diagnosis. Seventy-nine patients (68 families) were included in the cohort: 48 in group A, 23 in group B and 8 in group C. Fifty-one were considered confirmed CMS (30 CHRNE, 5 RAPSN, 4 COL13A1, 3 DOK7, 3 COLQ, 2 GFPT1, 1 CHAT, 1 SCN4A, 1 GMPPB, 1 CHRNA1), 7 probable CMS, 5 non-CMS and 16 unsolved. The chance of a confirmed molecular diagnosis of CMS was significantly higher for group A and lower for group C. Some individual clinical features, alterations on biopsy and electrophysiology enhanced specificity for CMS. Muscle imaging showed at least mild alterations in the majority of confirmed cases, with preferential involvement of soleus, especially in CHRNE CMS. Stricter clinical criteria increase the chance of confirming a CMS diagnosis, but may lose sensitivity, especially for some specific genes.

Generation and characterization of an induced pluripotent stem cell line SDQLCHi018-A from a congenital myasthenic syndrome patient carrying compound heterozygote mutations in RAPSN gene

Mutations in RAPSN are an important cause of congenital myasthenic syndrome (CMS). In this study, we generated an induced pluripotent stem cell line (iPSC) derived from a 14-day-old male CMS patient carrying compound heterozygote mutations (c.532-2A>G and c.264C>A/p.Asn88Lys) in RAPSN gene. The established iPSC line harboring the original mutations, possessing a normal karyotype, is able to differentiate into all three germ layers in vitro and expresses pluripotency markers.

AChR β-Subunit mRNAs Are Stabilized by HuR in a Mouse Model of Congenital Myasthenic Syndrome With Acetylcholinesterase Deficiency.

Collagen Q (COLQ) is a specific collagen that anchors acetylcholinesterase (AChE) in the synaptic cleft of the neuromuscular junction. So far, no mutation has been identified in the ACHE human gene but over 50 different mutations in the COLQ gene are causative for a congenital myasthenic syndrome (CMS) with AChE deficiency. Mice deficient for COLQ mimic most of the functional deficit observed in CMS patients. At the molecular level, a striking consequence of the absence of COLQ is an increase in the levels of acetylcholine receptor (AChR) mRNAs and proteins in vivo and in vitro in murine skeletal muscle cells. Here, we decipher the mechanisms that drive AChR mRNA upregulation in cultured muscle cells deficient for COLQ. We show that the levels of AChR β-subunit mRNAs are post-transcriptionally regulated by an increase in their stability. We demonstrate that this process results from an activation of p38 MAPK and the cytoplasmic translocation of the nuclear RNA-binding protein human antigen R (HuR) that interacts with the AU-rich element located within AChR β-subunit transcripts. This HuR/AChR transcript interaction induces AChR β-subunit mRNA stabilization and occurs at a specific stage of myogenic differentiation. In addition, pharmacological drugs that modulate p38 activity cause parallel modifications of HuR protein and AChR β-subunit levels. Thus, our study provides new insights into the signaling pathways that are regulated by ColQ-deficiency and highlights for the first time a role for HuR and p38 in mRNA stability in a model of congenital myasthenic syndrome.

Congenital myasthenic syndromes in the Thai population: Clinical findings and novel mutations

Congenital myasthenic syndromes (CMS) comprise a heterogeneous group of genetic disorders of the neuromuscular junction. Next generation sequencing has been increasingly used for molecular diagnosis in CMS patients. This study aimed to identify the disease-causing variants in Thai patients. We recruited patients with a diagnosis of CMS based on clinical and electrophysiologic findings, and whole exome sequencing was performed. Thirteen patients aged from 2 to 54 years (median: 8 years) from 12 families were enrolled. Variants were identified in 9 of 13 patients (69%). Five novel variants and two previously reported variant were found in the COLQ, RAPSN and CHRND gene. The previously reported c.393+1G>A splice site variant in the COLQ gene was found in a majority of patients. Five patients harbor the homozygous splice site c.393+1G>A variant, and two patients carry compound heterozygous c.393+1G>A, c.718–1G>T, and c.393+1G>A, c.865G>T (p.Gly289Ter) variants. The novel variants were also found in RAPSN (p.Cys251del, p.Arg282Cys) and CHRND (p.Met481del). Molecular diagnosis in CMS patients can guide treatment decisions and may be life changing, especially in patients with COLQ mutations.

Congenital myasthenic syndrome-associated agrin variants affect clustering of acetylcholine receptors in a domain-specific manner.

Congenital myasthenic syndromes (CMS) are caused by mutations in molecules expressed at the neuromuscular junction. We report clinical, structural, ultrastructural, and electrophysiologic features of 4 CMS patients with 6 heteroallelic variants in AGRN, encoding agrin. One was a 7.9-kb deletion involving the N-terminal laminin-binding domain. Another, c.4744G>A - at the last nucleotide of exon 26 - caused skipping of exon 26. Four missense mutations (p.S1180L, p.R1509W, p.G1675S, and p.Y1877D) expressed in conditioned media decreased AChR clusters in C2C12 myotubes. The agrin-enhanced phosphorylation of MuSK was markedly attenuated by p.Y1877D in the LG3 domain and moderately attenuated by p.R1509W in the LG1 domain but not by the other 2 mutations. The p.S1180L mutation in the SEA domain facilitated degradation of secreted agrin. The p.G1675S mutation in the LG2 domain attenuated anchoring of agrin to the sarcolemma by compromising its binding to heparin. Anchoring of agrin with p.R1509W in the LG1 domain was similarly attenuated. Mutations of agrin affect AChR clustering by enhancing agrin degradation or by suppressing MuSK phosphorylation and/or by compromising anchoring of agrin to the sarcolemma of the neuromuscular junction.

Congenital myasthenic syndrome: Ten years clinical experience from a quaternary care south-Indian hospital

BackgroundTo ascertain the frequency, clinical spectrum and outcome of congenital myasthenic syndrome (CMS) patients who reported to the neuromuscular division of our quaternary medical center during the past ten years. MethodsWe performed a retrospective analysis of all the CMS patients who reported to us during the study period. ResultsTwenty-one patients of CMS attended our quaternary hospital over the past ten years. The median follow-up was 24 (IQR: 16.5–67.3) months. All the patients showed an overall improvement in the last follow up. The diagnosis of CMS could be genetically confirmed in seven cases. Four patients had COLQ mutation, two had CHRNε mutation and one had MUSK mutation. All the cases of COLQ mutation and one case of MUSK mutation had a limb-girdle (LG) presentation. Our study and review of literature imply that CMS should be suspected in cases of seronegative myasthenia gravis cases if the onset is at less than 20 years and strongly so if the onset is within the first two years of life. In addition, a positive family history, delayed motor milestones, and a poor response to immune-modulators should be actively sought for as indicators of CMS.

I.2New genes and better treatment for congenital myasthenic syndromes

The congenital myasthenic syndromes (CMS) are rare inherited disorders of neuromuscular transmission characterised by fatiguable muscle weakness. Their overall prevalence is uncertain but is thought to be in the order of 1 in 100 000 of the population in the UK. They are genetically determined (usually autosomal recessive - so a history of consanguinity is common), non-autoimmune disorders. Remarkable differences in severity occur even within families harboring the same mutation. Although impairment of neuromuscular transmission may often give rise to similar clinical presentation many distinct molecular and cellular mechanisms may be involved. It has become evident over the last ten years that impaired synaptic structure and stability are disease features of equal importance as defects in proteins directly involved in signal transmission. Understanding the molecular mechanisms that underlie impaired synaptic transmission helps guide appropriate and often life-transforming therapy. What has also become evident is that for forms of CMS in which synaptic structure is disrupted, treatment with β2-adrengic receptor agonists is highly effective. Cases where components of the AGRN-LRP4-MUSK-DOK7 AChR clustering pathway are mutated usually respond well to this form of medication. Moreover, in CMS patients and in animal models of CMS long term treatment with pyridostigmine may be detrimental to synaptic structure but can be partially alleviated by treatment with β2-adrengic receptor agonists. The benefit of β2-adrenergic agonists alone or combined with pyridostigmine or 3,4-Diaminopyridine is increasingly becoming an effective part of the repertoire for treating many different subtypes of CMS.

Collagen XIII Is Required for Neuromuscular Synapse Regeneration and Functional Recovery after Peripheral Nerve Injury.

Collagen XIII occurs as both a transmembrane-bound and a shed extracellular protein and is able to regulate the formation and function of neuromuscular synapses. Its absence results in myasthenia: presynaptic and postsynaptic defects at the neuromuscular junction (NMJ), leading to destabilization of the motor nerves, muscle regeneration and atrophy. Mutations in COL13A1 have recently been found to cause congenital myasthenic syndrome, characterized by fatigue and chronic muscle weakness, which may be lethal. We show here that muscle defects in collagen XIII-deficient mice stabilize in adulthood, so that the disease is not progressive until very late. Sciatic nerve crush was performed to examine how the lack of collagen XIII or forced expression of its transmembrane form affects the neuromuscular synapse regeneration and functional recovery following injury. We show that collagen XIII-deficient male mice are unable to achieve complete NMJ regeneration and functional recovery. This is mainly attributable to presynaptic defects that already existed in the absence of collagen XIII before injury. Shedding of the ectodomain is not required, as the transmembrane form of collagen XIII alone fully rescues the phenotype. Thus, collagen XIII could serve as a therapeutic agent in cases of injury-induced PNS regeneration and functional recovery. We conclude that intrinsic alterations at the NMJ in Col13a1-/- mice contribute to impaired and incomplete NMJ regeneration and functional recovery after peripheral nerve injury. However, such alterations do not progress once they have stabilized in early adulthood, emphasizing the role of collagen XIII in NMJ maturation.SIGNIFICANCE STATEMENT Collagen XIII is required for gaining and maintaining the normal size, complexity, and functional capacity of neuromuscular synapses. Loss-of-function mutations in COL13A1 cause congenital myasthenic syndrome 19, characterized by postnatally progressive muscle fatigue, which compromises patients' functional capacity. We show here in collagen XIII-deficient mice that the disease stabilizes in adulthood once the NMJs have matured. This study also describes a relevant contribution of the altered NMJ morphology and function to neuromuscular synapses, and PNS regeneration and functional recovery in collagen XIII-deficient mice after peripheral nerve injury. Correlating the animal model data on collagen XIII-associated congenital myasthenic syndrome, it can be speculated that neuromuscular connections in congenital myasthenic syndrome patients are not able to fully regenerate and restore normal functionality if exposed to peripheral nerve injury.

Muscle magnetic resonance imaging in congenital myasthenic syndromes.

ABSTRACTIntroductionIn this study we investigated muscle magnetic resonance imaging in congenital myasthenic syndromes (CMS).MethodsTwenty‐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.ResultsOverall 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.ConclusionsMRI 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 Nerve 54: 211–219, 2016

Global N-linked Glycosylation is Not Significantly Impaired in Myoblasts in Congenital Myasthenic Syndromes Caused by Defective Glutamine-Fructose-6-Phosphate Transaminase 1 (GFPT1).

Glutamine-fructose-6-phosphate transaminase 1 (GFPT1) is the first enzyme of the hexosamine biosynthetic pathway. It transfers an amino group from glutamine to fructose-6-phosphate to yield glucosamine-6-phosphate, thus providing the precursor for uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) synthesis. UDP-GlcNAc is an essential substrate for all mammalian glycosylation biosynthetic pathways and N-glycan branching is especially sensitive to alterations in the concentration of this sugar nucleotide. It has been reported that GFPT1 mutations lead to a distinct sub-class of congenital myasthenic syndromes (CMS) termed “limb-girdle CMS with tubular aggregates”. CMS are hereditary neuromuscular transmission disorders in which neuromuscular junctions are impaired. To investigate whether alterations in protein glycosylation at the neuromuscular junction might be involved in this impairment, we have employed mass spectrometric strategies to study the N-glycomes of myoblasts and myotubes derived from two healthy controls, three GFPT1 patients, and four patients with other muscular diseases, namely CMS caused by mutations in DOK7, myopathy caused by mutations in MTND5, limb girdle muscular dystrophy type 2A (LGMD2A), and Pompe disease. A comparison of the relative abundances of bi-, tri-, and tetra-antennary N-glycans in each of the cell preparations revealed that all samples exhibited broadly similar levels of branching. Moreover, although some differences were observed in the relative abundances of some of the N-glycan constituents, these variations were modest and were not confined to the GFPT1 samples. Therefore, GFPT1 mutations in CMS patients do not appear to compromise global N-glycosylation in muscle cells.

Congenital myasthenic syndrome in Japan: Ethnically unique mutations in muscle nicotinic acetylcholine receptor subunits

Congenital myasthenic syndromes (CMS) are caused by mutations in genes expressed at the neuromuscular junction. Most CMS patients have been reported in Western and Middle Eastern countries, and only four patients with COLQ mutations have been reported in Japan. We here report six mutations in acetylcholine receptor (AChR) subunit genes in five Japanese patients. Five mutations are novel, and one mutation is shared with a European American patient but with a different haplotype. Among the observed mutations, p.Thr284Pro (p.Thr264Pro according to the legacy annotation) in the epsilon subunit causes a slow-channel CMS. Five other mutations in the delta and epsilon subunits are splice site, frameshift, null, or missense mutations causing endplate AChR deficiency. We also found a heteroallelic p.Met465Thr in the beta subunit in another patient. p.Met465Thr, however, was likely to be polymorphism, because single channel recordings showed mild shortening of channel openings without affecting cell surface expression of AChR, and the minor allelic frequency of p.Met465Thr was 5.1% in the Japanese population. Lack of shared mutant alleles between the Japanese and the other patients suggests that most mutations described here are ethnically unique or de novo in each family.

O.21 Congenital Myasthenic Syndrome (CMS), autophagic myopathy, and cognitive dysfunction caused by mutations in DPAGT1

We recently identified two CMS patients with CNS involvement. Patient 1 is a16-year-old mentally retarded girl with severe generalized CMS since infancy. One of her siblings is also affected and has autistic features. Patient 2 is a 14-year-old girl with mild cognitive deficits and progressive limb-girdle CMS since infancy. Both respond poorly to anti-AChE therapy. Intercostal muscle specimens in both show small tubular aggregates in type 2 fibers, type1 fiber atrophy, and a vacuolar myopathy with autophagic features. Endplate studies reveal that quantal release, postsynaptic response to acetylcholine, and endplate AChR content are reduced to ∼50% of normal. Quantitative EM of 65 endplate regions shows hypoplastic endplates, very small nerve terminals, and poorly differentiated postsynaptic regions. Neither patient harbors mutations in currently recognized CMS disease genes but exome sequencing in each identified two heteroallelic mutations in DPAGT1 coding for dolichyl-phosphate N-acetylglucosamine phosphotransferase, an enzyme subserving protein N-glycosylation. Immunoblots of muscle extracts probed by two different antibodies demonstrates reduced to absent glycosylation of ∼70 kDa proteins in Patient 1 but not in Patient 2. We conclude that DPAGT1 mutations result in both pre- and postsynaptic structural and electrophysiologic abnormalities. We hypothesize that hypoglycosylation of synapse-specific proteins causes defects in motor as well as central synapses. We recently identified two CMS patients with CNS involvement. Patient 1 is a16-year-old mentally retarded girl with severe generalized CMS since infancy. One of her siblings is also affected and has autistic features. Patient 2 is a 14-year-old girl with mild cognitive deficits and progressive limb-girdle CMS since infancy. Both respond poorly to anti-AChE therapy. Intercostal muscle specimens in both show small tubular aggregates in type 2 fibers, type1 fiber atrophy, and a vacuolar myopathy with autophagic features. Endplate studies reveal that quantal release, postsynaptic response to acetylcholine, and endplate AChR content are reduced to ∼50% of normal. Quantitative EM of 65 endplate regions shows hypoplastic endplates, very small nerve terminals, and poorly differentiated postsynaptic regions. Neither patient harbors mutations in currently recognized CMS disease genes but exome sequencing in each identified two heteroallelic mutations in DPAGT1 coding for dolichyl-phosphate N-acetylglucosamine phosphotransferase, an enzyme subserving protein N-glycosylation. Immunoblots of muscle extracts probed by two different antibodies demonstrates reduced to absent glycosylation of ∼70 kDa proteins in Patient 1 but not in Patient 2. We conclude that DPAGT1 mutations result in both pre- and postsynaptic structural and electrophysiologic abnormalities. We hypothesize that hypoglycosylation of synapse-specific proteins causes defects in motor as well as central synapses.

P.12.6 Congenital myasthenic syndromes: Diagnosis difficulties, course and prognosis, and therapy – The French CMS 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 the members of the French CMS network: the difficulties to make a proper diagnosis, the course and long term prognosis, and the response to therapy, especially for the CMS that do not respond to cholinesterase inhibitors. CMS diagnosis was late in most cases due to confusion with other entities: congenital myopathies, due to the frequent myopathic presentation of patients including permanent weakness, atrophy, scoliosis, and biopsy often showing abnormalities of internal structure, diameter and distribution of fibers (type I predominance, type II atrophy); seronegative autoimmune myasthenia gravis when CMS was late onset; metabolic myopathy, with presence of lipidosis in muscle. We studied long term prognosis of CMS in a series of 81 patients recruited with the following mutated genes: CHRNA, CHRNE, DOK7, COLQ, RAPSN, AGRN, MUSK. Course pattern (progressive worsening, exacerbation, stability, improvement) could be variable along the life in one single patient. DOK7 patients had the most severe course with progressive worsening: among the 8 wheel-chair bound and ventilated, 6 were mutated for this gene. Pregnancy was a frequent cause of exacerbation. Anticholinesterase agents are the first line therapy for CMS patients, except for Slow-Channel, COLQ and DOK7. In our experience, 3,4-DAP was a useful complement for several patients harboring CMS with AChR loss CMS or RAPSN gene mutations. Ephedrine was given to 18 patients (8 DOK7, 5 COLQ, 4 AGRN, 1 RAPSN). Tolerance was good. Therapeutic response was encouraging even in the most severely affected patients, particularly with DOK7 and COLQ. Salbutamol was a good alternative in one patient, allergic to Ephedrine.

Multiexon deletions account for 15% of congenital myasthenic syndromes with RAPSN mutations after negative DNA sequencing

Congenital myasthenic syndromes (CMS) are a heterogeneous group of genetic disorders that give rise to a defect in neuromuscular transmission. We described here three patients with a characteristic phenotype of...