Presynaptic Congenital Myasthenic Syndrome Research Articles

Expanding the genetic and phenotypic spectrum of congenital myasthenic syndrome: new homozygous VAMP1 splicing variants in 2 novel individuals.

We report the cases of two Spanish pediatric patients with hypotonia, muscle weakness and feeding difficulties at birth. Whole-exome sequencing (WES) uncovered two new homozygous VAMP1 (Vesicle Associated Membrane Protein 1) splicing variants, NM_014231.5:c.129+5 G > A in the boy patient (P1) and c.341-24_341-16delinsAGAAAA in the girl patient (P2). This gene encodes the vesicle-associated membrane protein 1 (VAMP1) that is a component of a protein complex involved in the fusion of synaptic vesicles with the presynaptic membrane. VAMP1 has a highly variable C-terminus generated by alternative splicing that gives rise to three main isoforms (A, B and D), being VAMP1A the only isoform expressed in the nervous system. In order to assess the pathogenicity of these variants, expression experiments of RNA for VAMP1 were carried out. The c.129+5 G > A and c.341-24_341-16delinsAGAAAA variants induced aberrant splicing events resulting in the deletion of exon 2 (r.5_131del; p.Ser2TrpfsTer7) in the three isoforms in the first case, and the retention of the last 14 nucleotides of the 3' of intron 4 (r.340_341ins341-14_341-1; p.Ile114AsnfsTer77) in the VAMP1A isoform in the second case. Pathogenic VAMP1 variants have been associated with autosomal dominant spastic ataxia 1 (SPAX1) and with autosomal recessive presynaptic congenital myasthenic syndrome (CMS). Our patients share the clinical manifestations of CMS patients with two important differences: they do not show the typical electrophysiological pattern that suggests pathology of pre-synaptic neuromuscular junction, and their muscular biopsies present hypertrophic fibers type 1. In conclusion, our data expand both genetic and phenotypic spectrum associated with VAMP1 variants.

Adeno-Associated Virus Type 9-Mediated Gene Therapy of Choline Acetyltransferase-Deficient Mice.

The enzyme choline acetyltransferase (ChAT) synthesizes acetylcholine from acetyl-CoA and choline at the neuromuscular junction and at the nerve terminals of cholinergic neurons. Mutations in the ChAT gene (CHAT) result in a presynaptic congenital myasthenic syndrome (CMS) that often associates with life-threatening episodes of apnea. Knockout mice for Chat (Chat-/-) die at birth. To circumvent the lethality of this model, we crossed mutant mice possessing loxP sites flanking Chat exons 4 and 5 with mice that expressed Cre-ERT2. Injection of tamoxifen (Tx) at postnatal (P) day 11 in these mice induced downregulation of Chat, autonomic failure, weakness, and death. However, a proportion of Chatflox/flox-Cre-ERT2 mice receiving at birth an intracerebroventricular injection of 2 × 1013 vg/kg adeno-associated virus type 9 (AAV9) carrying human CHAT (AAV9-CHAT) survived a subsequent Tx injection and lived to adulthood without showing signs of weakness. Likewise, injection of AA9-CHAT by intracisternal injection at P28 after the onset of weakness also resulted in survival to adulthood. The expression of Chat in spinal motor neurons of Chatflox/flox-Cre-ERT2 mice injected with Tx was markedly reduced, but AAV-injected mice showed a robust recovery of ChAT expression, which was mainly translated by the human CHAT RNA. The biodistribution of the viral genome was widespread but maximal in the spinal cord and brain of AAV-injected mice. No significant histopathological changes were observed in the brain, liver, and heart of AAV-injected mice after 1 year follow-up. Thus, AAV9-mediated gene therapy may provide an effective and safe treatment for patients severely affected with CHAT-CMS.

Presynaptic Congenital Myasthenic Syndromes: Understanding Clinical Phenotypes through In vivo Models.

Presynaptic congenital myasthenic syndromes (CMS) are a group of genetic disorders affecting the presynaptic side of the neuromuscular junctions (NMJ). They can result from a dysfunction in acetylcholine (ACh) synthesis or recycling, in its packaging into synaptic vesicles, or its subsequent release into the synaptic cleft. Other proteins involved in presynaptic endplate development and maintenance can also be impaired.Presynaptic CMS usually presents during the prenatal or neonatal period, with a severe phenotype including congenital arthrogryposis, developmental delay, and apnoeic crisis. However, milder phenotypes with proximal muscle weakness and good response to treatment have been described. Finally, many presynaptic genes are expressed in the brain, justifying the presence of additional central nervous system symptoms.Several animal models have been developed to study CMS, providing the opportunity to identify disease mechanisms and test treatment options. In this review, we describe presynaptic CMS phenotypes with a focus on in vivo models, to better understand CMS pathophysiology and define new causative genes.

Congenital Myasthenic Syndromes

Very few areas of medical genetics have been so profoundly impacted by the advent of next- generation sequencing (NGS) as the field of congenital myasthenic syndromes (CMS). This is due to the formidable genetic heterogeneity of CMS, a dearth of diagnostic clinical clues of CMS types, and the imperative need to establish an accurate molecular diagnosis of CMS type before any medication is started. A molecular diagnosis of CMS is fundamental not only to provide an appropriate therapy, but more importantly, to avoid potential deleterious treatments. Thus, NGS has transformed the tedious and expensive task of searching for causative mutations in an ever-expanding list of genes linked to CMS into an effective, and relatively inexpensive process that can rapidly identify the variant of CMS in question. One of the consequences of this transformation is a paradigm shift in the clinical practice of CMS that no longer requires, with rare exceptions, the use of special muscle biopsies that enable the analysis of the function and ultrastructure of the neuromuscular junction to determine the type of CMS. Another technological advance of recent years is CRISPR/Cas9, which allows genome editing at the zygotic stage, thus greatly simplifying the generation of mouse models carrying the same human CMS mutations in orthologous mouse genes. This permits an in-depth analysis of the pathogenesis and treatments of CMS caused by specific gene mutations. In terms of therapy, in addition to the classical pharmacologic treatments of CMS, including pyridostigmine sulfate, albuterol and 3,4 diaminopyridine, AAV-based gene therapies are now at the preclinical stage for several types of CMS. In this brief review, CMS are classified in six major groups: (1). presynaptic CMS, (2) synaptic CMS, (3) postsynaptic CMS; 4. CMS affecting the agrin-signal transduction pathway, (5) CMS linked to disorders of glycosylation, and (6) CMS associated with abnormalities of the cytoskeleton.

VAMP-1 associated congenital myasthenic syndrome: a demonstrative case with response to low-dose pyridostigmine (P2-8.003)

<h3>Objective:</h3> To report a case of VAMP1-associated congenital myasthenic syndrome with response to low-dose pyridostigmine, adding to an emerging literature describing this condition. <h3>Background:</h3> Biallelic mutations in VAMP1 are associated with a rare pre-synaptic congenital myasthenic syndrome (CMS). VAMP1 encodes a protein involved in synaptic vesicles formation and fusion. <h3>Design/Methods:</h3> Case report and review of literature <h3>Results:</h3> A 15 month-old boy was referred for evaluation of hypotonia and dysphagia since birth at term. The infant was unable to sit or roll. He was unable to feed orally. Examination revealed myopathic facies, fluctuating ptosis, ophthalmoparesis, hypotonia, and areflexia. Cry was weak. Secretion control was poor. Spontaneous movement was minimal; movements were antigravity in the distal extremities. Results of a prior Whole Exome Sequence identified a homozygous pathogenic variant in VAMP1 [ c.103C&lt;T; p.Q35* (NM_014231.3)]. A proactive airway clearance regimen was instituted. Pyridostigmine (0.25 mg/kg per dose) demonstrated immediate benefit, as indicated by antigravity movement of limbs, louder cry and cough, and improved secretion control despite being admitted for respiratory infection at the time of trial. Dose was increased to 0.5 mg/kg every four hours while awake. Parents observed more robust activity at home. Independent sitting was attained at age 17 months. Dysphagia persisted. A polysomnogram was abnormal (max ETCO2 50torr, AHI 9.8). <h3>Conclusions:</h3> This adds to the literature documenting a recessive VAMP1-related CMS. Recent reports have suggested pyridostigmine responsiveness. This case demonstrated motor benefit from low-dose pyridostigmine. Given risk of mucous plugging and aspiration in patients with neuromuscular weakness, an airway clearance regimen (ex: cough assist device) should be considered prior to a trial of therapy. Assessment of nocturnal ventilation and swallow safety remain crucial, as highlighted by this infant’s still abnormal polysomnogram and persistent dysphagia. <b>Disclosure:</b> Dr. Drakou has nothing to disclose. Dr. Delfiner has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Sarepta. Dr. Delfiner has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Novartis Gene Therapies. Dr. Delfiner has received personal compensation in the range of $500-$4,999 for serving as a MDA Engage Event Chair and speaker with Muscular Dystrophy Association.

RNA-SEQ ANALYSIS TO EXPLORE THE VARIANTS IN MELANOMA CELLS: MOLECULAR DIAGNOSIS AND THERAPEUTICS

High throughput sequencing technology that are also called as second generation or Next Generation (NGS) sequencing techniques has enabled researchers to study genome, transcriptome, metabolome of any organism in high throughput manner. RNA seq (Ribonucleic Acid Sequencing) is a NGS technique that is used to sequence total transcripts of cell and to study gene expression. This technique is widely used to identify differentially expressed genes and to identify variants. RNAseq technique has been used to study several diseases like cancers, neurological diseases, bacterial infections diseases and to understand the key mechanism of genes and its functions. Melanoma is a threatening tumor and one of the most successive metastatic diseases. Melanomas ordinarily happen inside the skin yet inside the mouth, digestion tracts or eye. Melanoma carcinoma is also called as cutaneous melanoma or melanoma of the skin. In current research Pair end RNA-seq sequencing data for melanoma cell was retrieved from ENA (European Nucleotide Archive) database with accession no.:SRP252675. RNAseq analysis pipeline of Galaxy online platform was used for the prediction of single nucleotide variations (SNVs). Total three genes are predicted that are expressed in RNAseq samples and involved in the skin cancer these genes are TNFRSF4 (Tumor Necrosis Factor Receptor Superfamily Member 4), TNFRSF18 and AGRN (Agrin). Protein encoded by TNFRSF4 gene is a member of the TNF-receptor superfamily and AGRN gene is associated with Presynaptic Congenital Myasthenic Syndromes. Pathway enrichment of identified genes shows that TNFRSF4 and TNFRSF18 have function in cytokine-cytokine receptor interaction and AGRN in ECM-receptor interaction. These results highlight the importance of TNFRSF4, TNFRSF18 and AGRN in Melanoma condition and can be further used as potential drug targets.

New recessive mutations in SYT2 causing severe presynaptic congenital myasthenic syndromes.

ObjectiveTo report the identification of 2 new homozygous recessive mutations in the synaptotagmin 2 (SYT2) gene as the genetic cause of severe and early presynaptic forms of congenital myasthenic syndromes (CMSs).MethodsNext-generation sequencing identified new homozygous intronic and frameshift mutations in the SYT2 gene as a likely cause of presynaptic CMS. We describe the clinical and electromyographic patient phenotypes, perform ex vivo splicing analyses to characterize the effect of the intronic mutation on exon splicing, and analyze the functional impact of this variation at the neuromuscular junction (NMJ).ResultsThe 2 infants presented a similar clinical phenotype evoking first a congenital myopathy characterized by muscle weakness and hypotonia. Next-generation sequencing allowed to the identification of 1 homozygous intronic mutation c.465+1G>A in patient 1 and another homozygous frameshift mutation c.328_331dup in patient 2, located respectively in the 5′ splice donor site of SYT2 intron 4 and in exon 3. Functional studies of the intronic mutation validated the abolition of the splice donor site of exon 4 leading to its skipping. In-frame skipping of exon 4 that encodes part of the C2A calcium-binding domain of SYT2 is associated with a loss-of-function effect resulting in a decrease of neurotransmitter release and severe pre- and postsynaptic NMJ defects.ConclusionsThis study identifies new homozygous recessive SYT2 mutations as the underlying cause of severe and early presynaptic form of CMS expanding the genetic spectrum of recessive SYT2-related CMS associated with defects in neurotransmitter release.

Presynaptic congenital myasthenic syndrome due to three novel mutations in SLC5A7 encoding the sodium-dependant high-affinity choline transporter

SLC5A7 encodes the presynaptic sodium-dependant high-affinity choline transporter 1 (CHT), which uptakes choline to the presynaptic nerve terminal following the breakdown of acetylcholine by the acetylcholinesterase within the synaptic cleft. We report 5 patients from three consanguineous families with congenital myasthenic syndrome type 20 caused by novel mutations in SLC5A7. The individuals from family 1 and 2 were homozygous for c.320G>A; (p.Arg107His) and c.886G>A (p.Ala296Thr), respectively, and their phenotype was characterised by recurrent apnoeic attacks early after birth and learning and speech difficulties in childhood. Individuals from family 3 were homozygous for c.1240T>A (p.Tyr414Asn) and suffered from more severe central and peripheral manifestations with lack of spontaneous movements and respiratory drive and overall minimal response to external stimuli. All individuals tested showed neurophysiological defects compatible with impaired neuromuscular transmission. Combined treatment with cholinesterase inhibitors and β2-adrenergic agonists was beneficial in patients from family 1 and 2. Affected individuals from family 3 died from complications directly related to their underlying genetic condition. This report provides three novel pathogenic variants in SLC5A7 and highlights the variability in the clinical phenotype, severity and prognosis of this syndrome.

Biallelic loss of function variants in SYT2 cause a treatable congenital onset presynaptic myasthenic syndrome.

Synaptotagmins are integral synaptic vesicle membrane proteins that function as calcium sensors and regulate neurotransmitter release at the presynaptic nerve terminal. Synaptotagmin-2 (SYT2), is the major isoform expressed at the neuromuscular junction. Recently, dominant missense variants in SYT2 have been reported as a rare cause of distal motor neuropathy and myasthenic syndrome, manifesting with stable or slowly progressive distal weakness of variable severity along with presynaptic NMJ impairment. These variants are thought to have a dominant-negative effect on synaptic vesicle exocytosis, although the precise pathomechanism remains to be elucidated. Here we report seven patients of five families, with biallelic loss of function variants in SYT2, clinically manifesting with a remarkably consistent phenotype of severe congenital onset hypotonia and weakness, with variable degrees of respiratory involvement. Electrodiagnostic findings were consistent with a presynaptic congenital myasthenic syndrome (CMS) in some. Treatment with an acetylcholinesterase inhibitor pursued in three patients showed clinical improvement with increased strength and function. This series further establishes SYT2 as a CMS-disease gene and expands its clinical and genetic spectrum to include recessive loss-of-function variants, manifesting as a severe congenital onset presynaptic CMS with potential treatment implications.

First report of a VAMP1 associated pre-synaptic congenital myasthenic syndrome from South-East Asia

Biallelic mutations in VAMP1, a member of synaptobrevin family have been reported previously to cause a rare form of pre-synaptic congenital myasthenic syndrome (CMS) in two middle-eastern families. We present a case of pre-synaptic CMS from Southern India with VAMP1 novel mutation identified by clinical exome sequencing (CES).Infomed consent obtained. A 5-year-old girl born to consanguineous parentage and delivered by LSCS for absent labour pains, developed respiratory distress and feeding difficulty postnatally requiring oxygen supplementation. Profound hypotonia, muscle weakness and ophthalmoparesis was observed during neonatal period. After 9 months of ryle’s tube feeding, percutaneous endoscopic gastrostomy (PEG) was performed. Fatigable ptosis, hypophonia and frequent lower respiratory tract infections were noticed from 2 years of age. She did not attain motor mile stones but attained normal mental milestones. Examination revealed myopathic facies, ophthalmoparesis, bifacial and bulbar weakness, contractures at ankle and knee, kyphoscoliosis and areflexia. Her elder sister died in neonatal period following meconium aspiration and respiratory distress. Her maternal cousin, a 12-year-old boy is reported to have fatiguable ocular, limb and bulbar weakness. Creatine kinase level was 366 IU/L. Child did not co-operate for repetitive nerve stimulation test. CES revealed a homozygous frameshift mutation c.66delT (p.Gly23AlafsTer6) in exon 2 of VAMP1 resulting in loss of v-SNARE domain important for vesicle docking at NMJ. Child showed mild improvement in neck, truncal movements and voice after 2 weeks of oral salbutamol and pyridostigmine. This is the first case report of VAMP1 pre-synaptic CMS from south-east Asia.

P.380: Bi-allelic loss of function mutations in SYT2 cause a congenital onset severe presynaptic myasthenic syndrome

Synaptotagmins are integral membrane proteins of the synaptic vesicles that function as calcium sensors and regulate neurotransmitter release at the presynaptic nerve. Synaptotagmin II, encoded by SYT2, is the major isoform expressed at the neuromuscular junction. Syt2 deficient mice are known to develop a lethal impairment in synaptic transmission with a reduction in evoked release of neurotransmitters at the neuromuscular junction, manifesting with progressive motor degeneration. Recently dominant missense mutations in SYT2 have been reported as a rare cause of distal motor neuropathy and myasthenic syndrome, clinically manifesting as a relatively stable or slowly progressive, distal weakness of variable expressivity with presynaptic NMJ impairment, responsive to 3,4 diaminopyridine treatment in some patients. While the exact pathogenic mechanism of these dominantly-acting SYT2 missense mutations remains largely unknown, they all impact the C2B calcium-binding domain and are thought to have a dominant-negative effect on synaptic vesicle exocytosis. Here we report four patients, of three independent families, with bi-allelic loss-of-function mutations in SYT2, clinically manifesting with a remarkably consistent phenotype of severe congenital-onset hypotonia and weakness, with electrodiagnostic findings consistent with a presynaptic congenital myasthenic syndrome (CMS). This case series further establishes SYT2 as a CMS-disease gene and expands its clinical and genetic spectrum to include recessive loss-of-function mutations, manifesting as a severe congenital-onset presynaptic CMS with potential treatment implications, thus warranting an early genetic diagnosis.

The Electrophysiology of Presynaptic Congenital Myasthenic Syndromes With and Without Facilitation: From Electrodiagnostic Findings to Molecular Mechanisms.

Congenital myasthenic syndromes (CMS) are a group of inherited disorders of neuromuscular transmission most commonly presenting with early onset fatigable weakness, ptosis, and ophthalmoparesis. CMS are classified according to the localization of the causative molecular defect. CMS with presynaptic dysfunction can be caused by mutations in several different genes, including those involved in acetylcholine synthesis, its packaging into synaptic vesicles, vesicle docking, and release from the presynaptic nerve terminal and neuromuscular junction development and maintenance. Electrodiagnostic testing is key in distinguishing CMS from other neuromuscular disorders with similar clinical features as well as for revealing features pointing to a specific molecular diagnosis. A decremental response on low-frequency repetitive nerve stimulation (RNS) is present in most presynaptic CMS. In CMS with deficits in acetylcholine resynthesis however, a decrement may only appear after conditioning with exercise or high-frequency RNS and characteristically displays a slow recovery. Facilitation occurs in CMS caused by mutations in VAMP1, UNC13A, SYT2, AGRN, LAMA5. By contrast, facilitation is absent in the other presynaptic CMS described to date. An understanding of the underlying molecular mechanisms therefore assists the interpretation of electrodiagnostic findings in patients with suspected CMS.

Choline transporter mutations in severe congenital myasthenic syndrome disrupt transporter localization.

The presynaptic, high-affinity choline transporter is a critical determinant of signalling by the neurotransmitter acetylcholine at both central and peripheral cholinergic synapses, including the neuromuscular junction. Here we describe an autosomal recessive presynaptic congenital myasthenic syndrome presenting with a broad clinical phenotype due to homozygous choline transporter missense mutations. The clinical phenotype ranges from the classical presentation of a congenital myasthenic syndrome in one patient (p.Pro210Leu), to severe neurodevelopmental delay with brain atrophy (p.Ser94Arg) and extend the clinical outcomes to a more severe spectrum with infantile lethality (p.Val112Glu). Cells transfected with mutant transporter construct revealed a virtually complete loss of transport activity that was paralleled by a reduction in transporter cell surface expression. Consistent with these findings, studies to determine the impact of gene mutations on the trafficking of the Caenorhabditis elegans choline transporter orthologue revealed deficits in transporter export to axons and nerve terminals. These findings contrast with our previous findings in autosomal dominant distal hereditary motor neuropathy of a dominant-negative frameshift mutation at the C-terminus of choline transporter that was associated with significantly reduced, but not completely abrogated choline transporter function. Together our findings define divergent neuropathological outcomes arising from different classes of choline transporter mutation with distinct disease processes and modes of inheritance. These findings underscore the essential role played by the choline transporter in sustaining acetylcholine neurotransmission at both central and neuromuscular synapses, with important implications for treatment and drug selection.

Homozygous mutations in VAMP1 cause a presynaptic congenital myasthenic syndrome.

We report 2 families with undiagnosed recessive presynaptic congenital myasthenic syndrome (CMS). Whole exome or genome sequencing identified segregating homozygous variants in VAMP1: c.51_64delAGGTGGGGGTCCCC in a Kuwaiti family and c.146G>C in an Israeli family. VAMP1 is crucial for vesicle fusion at presynaptic neuromuscular junction (NMJ). Electrodiagnostic examination showed severely low compound muscle action potentials and presynaptic impairment. We assessed the effect of the nonsense mutation on mRNA levels and evaluated the NMJ transmission in VAMP1 lew/lew mice, observing neurophysiological features of presynaptic impairment, similar to the patients. Taken together, our findings highlight VAMP1 homozygous mutations as a cause of presynaptic CMS. Ann Neurol 2017;81:597–603

Congenital myasthenic syndrome due to novel CHAT mutations in an ethnic kadazandusun family.

Choline acetyltransferase (CHAT) gene mutations cause a rare presynaptic congenital myasthenic syndrome due to impaired acetylcholine resynthesis. We report 2 Kadazandusun brothers with novel heterozygous CHAT mutations. The siblings were from a family of 7 children of nonconsanguineous parents, 3 who died from apneic crises. Both presented in infancy with ptosis and exertional limb weakness, but only 1 apnea episode was reported in the older sibling. The elder brother had a positive edrophonium test, and both were negative for acetylcholine receptor antibodies but improved with pyridostigmine treatment. A subsequent repetitive nerve stimulation test showed marked decremental response in the abductor digiti minimi only after prolonged ulnar nerve stimulation. Two novel CHAT gene mutations, p.Val306Leu and p.Ser704del were detected; the parents carried 1 mutation each. Differences in survival demonstrate phenotypic variability within the same family and a relatively good long-term outcome of the surviving siblings.

Electrophysiologic features of SYT2 mutations causing a treatable neuromuscular syndrome.

To describe the clinical and electrophysiologic features of synaptotagmin II (SYT2) mutations, a novel neuromuscular syndrome characterized by foot deformities and fatigable ocular and lower limb weakness, and the response to modulators of acetylcholine release. We performed detailed clinical and neurophysiologic assessment in 2 multigenerational families with dominant SYT2 mutations (c.920T>G [p.Asp307Ala] and c.923G>A [p.Pro308Leu]). Serial clinical and electrophysiologic assessments were performed in members of one family treated first with pyridostigmine and then with 3,4-diaminopyridine. Electrophysiologic testing revealed features indicative of a presynaptic deficit in neurotransmitter release with posttetanic potentiation lasting up to 60 minutes. Treatment with 3,4-diaminopyridine produced both a clinical benefit and an improvement in neuromuscular transmission. SYT2 mutations cause a novel and potentially treatable complex presynaptic congenital myasthenic syndrome characterized by motor neuropathy causing lower limb wasting and foot deformities, with reflex potentiation following exercise and a uniquely prolonged period of posttetanic potentiation.

Genetics of strabismus and lid diseases.

The prevalence of congenital ocular malformations has been described to vary from 0.04 to 6.8 per 10,000 live births. The nuclear mutations identified in chronic progressive external ophthalmoplegia harbor multiple mtDNA deletions that include POLG mutations, PEO1 mutations, OPA1 mutations and RRM2B mutations. In Kearns-Sayre syndrome, the spontaneous mitochondrial deletions vary from 1.3 to 8.0 kb subunits of the oxidative phosphorylation enzymes and several t-RNA genes are affected. Oculopharyngeal muscle dystrophy is both autosomal dominant and recessive form. Congenital fibrosis of extraocular muscles (CFEOM) 1 has mutations in KIF21A on chromosome 12 with TUBB3 mutation also being seen. CFEOM 2 is an autosomal recessive, genetically distinct entity with homozygous mutations in PHOX2A. CFEOM 3 is autosomal dominant heterozygous missense mutations in TUBB3. Most cases of Mobius syndrome are sporadic with familial cases being autosomal dominant, autosomal recessive or X-linked recessive inheritance. Genetic testing has shown abnormalities involving chromosome 1 and 13. Presynaptic congenital myasthenic syndrome is caused by ChAT (choline acetyltransferase) mutation. Two loci have been found for myotonic dystrophy (DM). DM1, which is associated with trinucleotide expansion on chromosome 19q13.3 and DM2 which is associated with CCTG tetranucleotide expansion at 3q21. Blepharophimosis is caused by mutations in the FOXL2 gene 49 located at chromosome 3q23. Lymphedema-distichiasis is an autosomal dominant disorder caused by mutations in the FOXC2 gene.

Synaptotagmin 2 Mutations Cause an Autosomal-Dominant Form of Lambert-Eaton Myasthenic Syndrome and Nonprogressive Motor Neuropathy

Synaptotagmin 2 is a synaptic vesicle protein that functions as a calcium sensor for neurotransmission but has not been previously associated with human disease. Via whole-exome sequencing, we identified heterozygous missense mutations in the C2B calcium-binding domain of the gene encoding Synaptotagmin 2 in two multigenerational families presenting with peripheral motor neuron syndromes. An essential calcium-binding aspartate residue, Asp307Ala, was disrupted by a c.920A>C change in one family that presented with an autosomal-dominant presynaptic neuromuscular junction disorder resembling Lambert-Eaton myasthenic syndrome. A c.923C>T variant affecting an adjacent residue (p.Pro308Leu) produced a presynaptic neuromuscular junction defect and a dominant hereditary motor neuropathy in a second family. Characterization of the mutation homologous to the human c.920A>C variant in Drosophila Synaptotagmin revealed a dominant disruption of synaptic vesicle exocytosis using this transgenic model. These findings indicate that Synaptotagmin 2 regulates neurotransmitter release at human peripheral motor nerve terminals. In addition, mutations in the Synaptotagmin 2 C2B domain represent an important cause of presynaptic congenital myasthenic syndromes and link them with hereditary motor axonopathies.

Long-term follow-up in patients with congenital myasthenic syndrome due to CHAT mutations

Background Congenital myasthenic syndromes (CMSs) are a group of clinically and genetically heterogeneous inherited disorders of the neuromuscular junction. Mutations in the acetylcholine transferase ( CHAT) gene cause a pre-synaptic CMS, typically associated with episodic apnoea and worsening of myasthenic symptoms during crises caused by infections, fever or stress. Between crises symptoms may be mild and variable. Acetylcholinesterase – inhibitor therapy is reported to improve clinical symptoms and reduce crises. Patients and methods We present data on the long-term follow-up of 11 patients with a congenital myasthenic syndrome due to nine different CHAT mutations; ten of the patients have not been previously reported. Results and conclusions Manifestation varied from the neonatal period to the age of two years, follow-up time from nine months to 12 years. This cohort of CHAT patients studied here enabled us to describe two distinct phenotypes: The neonatal-onset group suffers from apnoeic crises, respirator dependency and bulbar weakness. Apnoea should be carefully distinguished from seizures; a CMS should be taken into account early to start appropriate therapy. Infantile-onset patients show mild permanent weakness, but experience apnoeic crises and worsening which resolve with Acetylcholinesterase – inhibitor treatment. However, after several years of treatment proximal muscle strength may decrease and lead to wheelchair dependency despite the continuation of Acetylcholinesterase – inhibitor therapy.

Co-morbidity of Emery-Dreifuss muscular dystrophy and a congenital myasthenic syndrome possibly affecting the phenotype in a large Bedouin kindred

Emery-Dreifuss muscular dystrophy (EDMD) is an X-linked humero-peroneal muscular dystrophy associated with contractures and cardiomyopathy. In a 90 member family, we found 11 affected male individuals, three of whom displayed areflexia and neurogenic electromyographic changes. Muscle biopsy performed in one case demonstrated type grouping suggestive of a neurogenic disorder. These three individuals and another family member, who suffers from mild, static limb weakness but is clinically and genetically unaffected by EDMD showed an abnormal incremental response of over 100% to tetanic stimulation. In contrast, one affected family member showed myopathic features on needle electromyography and no definite pathology in repetitive stimulation studies. The diagnosis of EDMD was established by demonstrating a 1712_1713insTGGGC mutation in the emerin gene. This family apparently expresses co-morbidity of EDMD with an exceptionally mild form of pre-synaptic congenital myasthenic syndrome resembling the Lambert-Eaton myasthenic syndrome (LEMS). The superimposed pre-synaptic disorder may have contributed to the development of the neurogenic features demonstrated in these patients.