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Mechanism of disease and therapeutic rescue of Dok7 congenital myasthenia.

ABSTRACT: Congenital myasthenia (CM) is a devastating neuromuscular disease, and mutations in DOK7, an adaptor protein that is crucial for forming and maintaining neuromuscular synapses, are a major cause of CM^1,2. The most common disease-causing mutation (DOK7^{1124_1127 dup}) truncates DOK7 and leads to the loss of two tyrosine residues that are phosphorylated and recruit CRK proteins, which are important for anchoring acetylcholine receptors at synapses. Here we describe a mouse model of this common form of CM (Dok7^CM mice) and a mouse with point mutations in the two tyrosine residues (Dok7^2YF). We show that Dok7^CM mice had severe deficits in neuromuscular synapse formation that caused neonatal lethality. Unexpectedly, these deficits were due to a severe deficiency in phosphorylation and activation of muscle-specific kinase (MUSK) rather than a deficiency in DOK7 tyrosine phosphorylation. We developed agonist antibodies against MUSK and show that these antibodies restored neuromuscular synapse formation and prevented neonatal lethality and late-onset disease in Dok7^CM mice. These findings identify an unexpected cause for disease and a potential therapy for both DOK7 CM and other forms of CM caused by mutations in AGRIN, LRP4 or MUSK, and illustrate the potential of targeted therapy to rescue congenital lethality.

SUBMITTER: Oury J

PROVIDER: S-EPMC8277574 | biostudies-literature | 2021 Jul

REPOSITORIES: biostudies-literature

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Mechanism of disease and therapeutic rescue of Dok7 congenital myasthenia.

Oury Julien J Zhang Wei W Leloup Nadia N Koide Akiko A Corrado Alexis D AD Ketavarapu Gayatri G Hattori Takamitsu T Koide Shohei S Burden Steven J SJ

Nature 20210623 7867

Congenital myasthenia (CM) is a devastating neuromuscular disease, and mutations in DOK7, an adaptor protein that is crucial for forming and maintaining neuromuscular synapses, are a major cause of CM<sup>1,2</sup>. The most common disease-causing mutation (DOK7<sup>1124_1127 dup</sup>) truncates DOK7 and leads to the loss of two tyrosine residues that are phosphorylated and recruit CRK proteins, which are important for anchoring acetylcholine receptors at synapses. Here we describe a mouse mode ...[more]

PMID: 34163073

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Project description:Congenital myasthenic syndromes are a group of inherited disorders characterized by defective neuromuscular transmission and fatigable muscle weakness. Causative mutations have been identified in over 30 genes, including DOK7, a gene encoding a post-synaptic protein crucial in the formation and stabilization of the neuromuscular junction. Mutations in this gene are one of the leading three most prevalent causes of congenital myasthenia in diverse populations across the globe. The majority of DOK7 congenital myasthenic patients experience varying degrees of disability despite receiving optimized treatment (usually salbutamol), necessitating the development of improved therapeutic approaches. Here, we executed a dose escalation pre-clinical trial using a DOK7 congenital myasthenic syndrome mouse model to assess the efficacy of AMP-101, an innovative recombinant adeno-associated viral gene replacement therapy. This mouse model harbours a duplication in the Dok7 gene that corresponds to the mutation most commonly found in DOK7 congenital myasthenia patients, c.1124-1127dupTGCC. The model has a much more severe phenotype than patients, and lives for only a few days. AMP-101 is based on AAVrh74 and contains human DOK7 cDNA under the control of a muscle-restricted promoter. Three doses of AMP-101 (2 × 1013 vg/kg, 6 × 1013 vg/kg or 1 × 1014 vg/kg) were administered intraperitoneally at 4 days of age. We show that the two higher doses of 6 × 1013 vg/kg and 1 × 1014 vg/kg generated enlarged neuromuscular junctions and rescued the very severe phenotype of the model. Treated mice became at least as strong as wild-type littermates, as demonstrated by using an inverted screen hang test, a rotarod test and a grip strength test. EMG showed that the treated model mice had decrement of compound muscle action potential on repetitive nerve stimulation, which indicates defective signalling at the neuromuscular junction. However, male models treated with 1 × 1014 vg/kg showed the least decrement that was not statistically different from wild-type littermates. Western blot analysis demonstrated robust expression of DOK7 in the diaphragm and tibialis anterior muscles. These data show that AMP-101 is an effective treatment in a mouse model for DOK7 congenital myasthenia, and suggests that AMP-101 is a promising candidate to move forward to clinic trials as a gene therapy for patients.

Project description:BackgroundMyasthenia 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.ObjectivesTo assess the effects and adverse effects of ephedrine in people with autoimmune MG, transient neonatal MG, and the congenital myasthenic syndromes.Search methodsOn 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 criteriaWe 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 analysisTwo 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 resultsWe 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' conclusionsThere 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.

Dataset Information

Mechanism of disease and therapeutic rescue of Dok7 congenital myasthenia.

Publications

Mechanism of disease and therapeutic rescue of Dok7 congenital myasthenia.

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