Congenital myasthenic syndromes

Congenital myasthenic syndromes (CMS) are rare inherited neuromuscular disorders characterized by fatigable weakness of skeletal muscle owing to compromised function of the neuromuscular junction (NMJ). The first identified mutations were in genes encoding subunits of the acetylcholine receptor, and these remain the most common subtypes of CMS worldwide. With the advent of next-generation sequencing, the number of genetic defects reported as causative of a CMS phenotype has increased dramatically, with over 30 genes now implicated. However, between 20 and 40% of patients with CMS remain without a molecular diagnosis after exome sequencing, and part of our research focuses on gene discovery to solve these remaining unsolved cases through the latest genome sequencing and multi-omics approaches.

In many cases the pathomechanisms behind the disease are still not well understood, and our lab generates and works with cell, zebrafish and mouse models of various CMS subtypes in order to investigate the disease processes and look for therapeutic targets and disease modifiers.

Treatments for congenital myasthenia

Unlike the majority of neuromuscular disorders, congenital myasthenic syndromes are frequently treatable with common drugs that can significantly alleviate the severity of symptoms and restore some functional ability. Treatment varies by subtype, and treatment strategies are broadly dependent on whether it is beneficial to increase the amount of acetylcholine available in the synaptic cleft (for which commonly administered therapies include AChE inhibitors such as pyridostigmine, which inhibits acetylcholine breakdown, and the potassium-channel blocker 3,4-diaminopyridine, which increases the quantal release of acetylcholine) or to shorten the duration of synaptic current in slow-channel syndromes by reducing the channel-open time (for which the open-channel blockers fluoxetine and quinidine may be used). β2 adrenergic receptor agonists such as ephedrine and salbutamol (albuterol) are also widely prescribed for CMS. The mechanism of the therapeutic effect of β2 adrenergic receptor agonists in CMS is not understood, and our lab is investigating the mode of action of these drugs in specific CMS subtypes with the aim of exploring potential modifications to improve efficacy and better target treatment.
In collaboration with colleagues from the European Solve-RD project, we are working to develop a “treatabolome” for CMS – a database of treatable variants that can be incorporated into genetic databases and analysis systems in order to flag up to the treating clinician or geneticist that a potential treatment is available. The hope is that this will increase the speed with which individuals with CMS receive the correct treatment.

Read an article about the different CMS types and the way incorporating them into classification systems helps computer accessibility.

In collaboration with colleagues in Germany, we are currently working on the elucidation of the NMJ proteome and the establishment of a tailored assay enabling the robust quantification of NMJ-related proteins in various mouse models of this group of diseases.

Microscopy image of a neuromuscular junction

Relevant publications

Núñez-Carpintero, I, Rigau, M, Bosio, M, O'Connor, E, Spendiff, S, Azuma, Y et al.. Rare disease research workflow using multilayer networks elucidates the molecular determinants of severity in Congenital Myasthenic Syndromes. Nat Commun. 2024.15 (1)1227 PMID:38418480

Pugliese, A, Della Marina, A, de Paula Estephan, E, Zanoteli, E, Roos, A, Schara-Schmidt, U et al.. Mutations in PTPN11 could lead to a congenital myasthenic syndrome phenotype: a Noonan syndrome case series. J Neurol. 2024.271 (3)1331-1341 PMID:37923938

Özsoy, Ö, Cinleti, T, Günay, Ç, Sarıkaya Uzan, G, Yeşilmen, MC, Lochmüller, H et al.. DPAGT1-CDG: Report of Two New Pediatric Patients and Brief Review of the Literature. Mol Syndromol. 2023.14 (4)322-330 PMID:37766827

Polavarapu, K, Sunitha, B, Töpf, A, Preethish-Kumar, V, Thompson, R, Vengalil, S et al.. Clinical and genetic characterisation of a large Indian congenital myasthenic syndrome cohort. Brain. 2024.147 (1)281-296 PMID:37721175

O'Connor, K, Spendiff, S, Lochmüller, H, Horvath, R. Mitochondrial Mutations Can Alter Neuromuscular Transmission in Congenital Myasthenic Syndrome and Mitochondrial Disease. Int J Mol Sci. 2023.24 (10) PMID:37239850

Pugliese, A, Holland, SH, Rodolico, C, Lochmüller, H, Spendiff, S. Presynaptic Congenital Myasthenic Syndromes: Understanding Clinical Phenotypes through In vivo Models. J Neuromuscul Dis. 2023.10 (5)731-759 PMID:37212067

McMacken, G, Whittaker, RG, Wake, R, Lochmuller, H, Horvath, R. Neuromuscular junction involvement in inherited motor neuropathies: genetic heterogeneity and effect of oral salbutamol treatment. J Neurol. 2023.270 (6)3112-3119 PMID:36869887

Rodríguez Cruz, PM, Ravenscroft, G, Natera, D, Carr, A, Manzur, A, Liu, WW et al.. A novel phenotype of AChR-deficiency syndrome with predominant facial and distal weakness resulting from the inclusion of an evolutionary alternatively-spliced exon in CHRNA1. Neuromuscul Disord. 2023.33 (2)161-168 PMID:36634413

Senderek, J, Müller, JS, Dusl, M, Strom, TM, Guergueltcheva, V, Diepolder, I et al.. Hexosamine biosynthetic pathway mutations cause neuromuscular transmission defect. Am J Hum Genet. 2011.88 (2)162-72 PMID:21310273

Beeson, D, Higuchi, O, Palace, J, Cossins, J, Spearman, H, Maxwell, S et al.. Dok-7 mutations underlie a neuromuscular junction synaptopathy. Science. 2006.313 (5795)1975-8 PMID:16917026