Respiratory insufficiency as a presenting symptom of congenital myasthenic syndromes.

AIM: Respiratory insufficiency can be a presenting symptom of congenital myasthenic syndromes (CMS) but is rarely recognised as such. In this study, we aim to raise awareness of CMS to paediatricians. METHODS: We performed a retrospective case study of infants and preschool children treated in the past 5 years in Amalia Children's Hospital, Radboud University Medical Center in Nijmegen, the Netherlands for respiratory insufficiency as presenting symptom of CMS. RESULTS: Five children aged 2 weeks to 5 years experienced severe to life-threatening episodes of respiratory insufficiency, especially during viral infections, due to respiratory muscle weakness. During infections, they often also had progression of their otherwise mild ocular, facial, and limb muscle weakness. They were eventually diagnosed with genetically proven CMS. In these five children, treatment with pyridostigmine, an acetylcholinesterase inhibitor, resulted in clinical improvement. CONCLUSION: CMS should be considered in every patient with unexplained recurrent respiratory insufficiency, or with an unusually severe course of a normally mild respiratory infection, especially in combination with mild muscle weakness outside periods of illness. Early diagnosis of CMS is crucial for early treatment, which may help avoiding sudden infant death, severe respiratory insufficiency and further deterioration of the muscle strength.

The use of frontalis sling in the management of variable ptosis secondary to congenital myasthenic syndrome.

Congenital myasthenic syndrome (CMS) describes a group of rare inherited disorders caused by impaired neuromuscular transmission at the motor endplate. Common ophthalmic manifestations associated with CMS include ptosis and ophthalmoplegia. A 19-year-old female presented with variable day-to-day ptosis secondary to CMS that was refractory to medical therapy. Bilateral silicone frontalis slings were used to stabilise the upper lid height and reduce fluctuation in severity of ptosis. Blepharoptosis surgery has been performed in patients with chronic myasthenia gravis (MG), but rarely in the setting of CMS. Blepharoptosis surgery in CMS patients with variable ptosis is difficult due to the risk of upsetting the original lid position and developing post-operative exposure keratopathy. Our case demonstrates that the frontalis sling procedure may be considered as an option in the management of variable blepharoptosis secondary to CMS.

The longest reported sibling survivors of a severe form of congenital myasthenic syndrome with the ALG14 pathogenic variant.

Congenital myasthenic syndromes (CMS) is a group of diseases that causes abnormalities at the neuromuscular junction owing to genetic anomalies. The pathogenic variant in ALG14 results in a severe pathological form of CMS causing end-plate acetylcholine receptor deficiency. Here, we report the cases of two siblings with CMS associated with a novel variant in ALG14. Immediately after birth, they showed hypotonia and multiple joint contractures with low Apgar scores. Ptosis, low-set ears, and high-arched palate were noted. Deep tendon reflexes were symmetrical. They showed worsening swallowing and respiratory problems; hence, nasal feeding and tracheotomy were performed. Cranial magnetic resonance imaging scans revealed delayed myelination and cerebral atrophy. Exome sequencing indicated that the siblings had novel compound heterozygous missense variants, c.590T>G (p.Val197Gly) and c.433G>A (p.Gly145Arg), in exon 4 of ALG14. Repetitive nerve stimulation test showed an abnormal decrease in compound muscle action potential. After treatment with pyridostigmine, the time off the respirator increased. Their epileptic seizures were well controlled by anti-epileptic drugs. Their clinical course is stable even now at the ages of 5 and 2 years, making them the longest reported survivors of a severe form of CMS with the ALG14 variant thus far.

COVID-19 in a Cohort of Patients with Congenital Myasthenic Syndrome.

Congenital Myasthenic Syndromes (CMS) are a rare group of genetic disorders of neuromuscular transmission. Some subtypes of CMS can be associated with respiratory and bulbar weakness and these patients may therefore be at high risk of developing a severe disease from COVID-19. We screened 73 patients with genetically confirmed CMS who were attending the UK national referral centre for evidence of previous Severe Acute Respiratory Syndrome Corona Virus 2 infection and their clinical outcome. Of 73 patients, seven had history of confirmed COVID-19. None of the infected patients developed a severe disease, and there were no signals that CMS alone carries a high risk of severe disease from COVID-19.

Development of neovascular glaucoma after intraocular surgery in Pierson syndrome.

Purpose: To report a patient with Pierson syndrome who presented with neovascular glaucoma (NVG) after cataract surgery.Methods: Retrospective case report.Results: A 17-year old monocular female presented with sudden onset of pain and decreased vision in the right eye. On examination, she had intraocular pressure (IOP) of 50 mmHg, aggressive iris neovascularization (NVI) and 3-piece IOL. Fundus examination revealed pale disc with tessellated fundus and parapapillary atrophy. Vascular arcades were vertically stretched with avascular ischemic retina starting from the near periphery. Macula appeared thin and atrophic. An intravitreal injection of 0.05 mg/0.1 ml bevacizumab was given to the right eye followed by Ahmed glaucoma valve (AGV) implantation. Assessment of her brother revealed similar posterior segment changes. A subsequent urine analysis showed proteinuria and high albumin to creatinine ratio. Next-generation sequencing for LAMB2 gene revealed a homozygous c.4573 + 1 G > A variant confirming the diagnosis of Pierson syndrome.Conclusion: This case expands our knowledge on retinal ischemia in the setting of Pierson syndrome. Close monitoring after intraocular surgery is recommended to look for the development of NVG.

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.

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.

Obstructive sleep apnoea and hypoventilation in an adult with congenital myasthenic syndrome.

In this case report, we describe an adult male with congenital myasthenic syndrome due to mutations in muscle-specific receptor tyrosine kinase (MuSK, c.79+2 T>G; IVS1 +2 T>G, c.2368 G>A, Val790Met) presenting with sleep apnoea and hypercapnic respiratory failure. In the intensive care unit, he required intubation followed by tracheostomy which resolved obstructive sleep apnoea. Later, due to persistent sleep-associated hypoventilation, he required nocturnal mechanical ventilation. His case illustrates how respiratory muscle weakness due to mutations in MuSK can lead to various forms of sleep disordered breathing.

The Curse of Apneic Spells.

A 6-year-old girl had reduced fetal movements, numerous apneic spells, muscle hypotonia, and developmental motor delay. Her muscle biopsy tissue showed variation in myofiber diameters, small minicores by electron microscopy, and near-uniformity of type I fibers. Although no mutations were detected in RYR1, SEPN1, and DMPK genes, the RAPSN gene revealed one known mutation, p.Asn88Lys, from the mother, and one novel mutation, p.Cys366Gly, from the father. Life-saving pyridostigmine treatment suppressed her apneic spells and improved her motor development.

[Clinical and genetic characteristics of congenital myasthenia syndrome with episodic apnea caused by CHAT gene mutation: a report of 2 cases].

Objective: To investigate the clinical and genetic features of congenital myasthenia syndrome with episodic apnea (CMS-EA) caused by gene mutation of choline acetyltransferase (CHAT) Methods: The clinical data of 2 patients with congenital myasthenia syndrome were collected, and both were diagnosed from 2013 to 2015 in Beijing Children's Hospital, Capital Medical University. The clinical features and gene mutation characteristics were analyzed, and the patients were followed-up for therapeutic efficacy. Results: The two patients (case 1 and case 2) had the onset soon after birth and at 3 months after birth respectively. The two patients were admitted to the PICU due to dyspnea, cyanotic episodes that required intubation. The patients had repeated apnea and became ventilator dependent. Case 1 died due to refusal of any treatment. Case 2 had a tracheotomy, and gradually weaned from ventilator after using pyridostigmine. The hospitalization of case 2 lasted 162 days. Case 2 was followed up to the age of 3 years and 4 months, and was extubated and was maintained on oral neostigmine but still had fluctuating ptosis and minor physical and mental retardation. Both cases were negative for anti-AChR, anti-acetylcholinesterase, anti-MuSK antibodies. Neostigmine test was negative in case 1 and suspiciously positive in case 2. Low-frequency repetitive nerve stimulation testing of case 2 was negative. Cranial MRI scans of both cases showed brain atrophy-like change. Genetic testing showed compound heterozygous deletions (exon 4, 5, 6) and pathogenic variant c.914T>C (p.I305T) in CHAT in case 1, compound heterozygous variants c.1007T>C (p.I336T) and c.64C>T (p.Q22X) in CHAT in case 2. To our knowledge, compound heterozygous deletions (exon 4, 5, 6) and p.Q22X were novel, previously unreported variants. Conclusion: CMS-EA usually presents at birth or in the neonatal period with hypotonia, ptosis, dysphagia due to severe bulbar weakness, and respiratory insufficiency with cyanosis and apnea. Early treatment with pyridostigmine is helpful to the improvement of clinical symptoms and prognosis.

Mechanism hypotheses for the electrophysiological manifestations of two cases of endplate acetylcholinesterase deficiency related congenital myasthenic syndrome.

OBJECTIVE: To summarize the electrophysiological characteristics of two cases of endplate acetylcholinesterase deficiency (EAD) related congenital myasthenic syndrome (CMS) caused by COLQ mutation and to discuss the possible mechanism of these electrophysiological phenomena. METHODS: Electrophysiological examinations were conducted including nerve conduction studies, routine electromyography (EMG), repetitive nerve stimulation (RNS) and single fiber EMG (SFEMG). The ulnar nerve was also stimulated at 50 Hz followed by 0.5 Hz to record the recovery process of compound muscle action potential (CMAP). RESULTS: Repetitive CMAP (R-CMAP) was found in motor nerve conduction in both cases. Needle EMG showed myogenic damages and SFEMG showed remarkably increased jitter values. Of note, the amplitude of CMAP and R-CMAP showed regular changing trends, and so did their time intervals in RNS studies. CONCLUSIONS: The change patterns of CMAP and R-CMAP, in combination with other electrophysiological features are very useful for the diagnosis of EAD related CMS, especially in predicting the presence of correct gene mutations.

Sleep in infants with congenital myasthenic syndromes.

BACKGROUND AND OBJECTIVES: Infants with congenital myasthenic syndrome (CMS) are at risk of brief resolved unexplained event (BRUE) and sleep-disordered breathing. The aim of the study was to explore sleep in infants with CMS with a particular focus on heart rate (HR) variability. METHODS: Overnight polygraphy was performed and HR variations associated with respiratory events were analysed. Bradycardia and tachycardia were defined as a variation of HR of ±10 bpm from baseline and analysed as events/hour. RESULTS: The data of 5 infants with CMS were analysed. Two patients had known mutations (COLQ and RAPSN). One patient had a tracheostomy. The apnoea-hypopnoea index (AHI) was abnormal in all the patients (range 2.8-47.7 events/h), with the highest AHI being observed in the 3 youngest infants. Nocturnal transcutaneous gas exchange was normal in all patients except the tracheostomised patient. Mean HR was 114 ± 23 bpm with a mean HR index of 4.5 ± 4.3 events/h. The amplitudes of HR variations (bradycardia or tachycardia) were around 15-20 bpm, regardless of the type of respiratory event, and comparable between patients. No correlations were found between HR indexes or variations and the type and mean duration of respiratory events. Ventilatory support was initiated in 3 infants immediately after the sleep study because of a high AHI and/or nocturnal hypoventilation. CONCLUSIONS: All 5 infants had an abnormal AHI with younger infants having the highest AHI. Three infants required ventilatory support after the polygraphy, underlining its clinical usefulness. No significant abnormalities of HR were observed during the sleep studies.

Presynaptic congenital myasthenic syndrome with a homozygous sequence variant in LAMA5 combines myopia, facial tics, and failure of neuromuscular transmission.

Defects in genes encoding the isoforms of the laminin alpha subunit have been linked to various phenotypic manifestations, including brain malformations, muscular dystrophy, ocular defects, cardiomyopathy, and skin abnormalities. We report here a severe defect of neuromuscular transmission in a consanguineous patient with a homozygous variant in the laminin alpha-5 subunit gene (LAMA5). The variant c.8046C>T (p.Arg2659Trp) is rare and has a predicted deleterious effect. The affected individual, who also carries a rare homozygous sequence variant in LAMA1, had muscle weakness, myopia, and facial tics. Magnetic resonance imaging of brain showed mild volume loss and periventricular T2 prolongation. Repetitive nerve stimulation revealed 50% decrement of compound muscle action potential amplitudes and 250% facilitation immediately after exercise, Endplate studies identified a profound reduction of the endplate potential quantal content and endplates with normal postsynaptic folding that were denuded or partially occupied by small nerve terminals. Expression studies revealed that p.Arg2659Trp caused decreased binding of laminin alpha-5 to SV2A and impaired laminin-521 cell-adhesion and cell projection support in primary neuronal cultures. In summary, this report describing severe neuromuscular transmission failure in a patient with a LAMA5 mutation expands the list of phenotypes associated with defects in genes encoding alpha-laminins.