Point Mutations of Nicotinic Receptor α1 Subunit Reveal New Molecular Features of G153S Slow-Channel Myasthenia

Slow-channel congenital myasthenic syndromes (SCCMSs) are rare genetic diseases caused by mutations in muscle nicotinic acetylcholine receptor (nAChR) subunits. Most of the known SCCMS-associated mutations localize at the transmembrane region near the ion pore. Only two SCCMS point mutations are at the extracellular domains near the acetylcholine binding site, α1(G153S) being one of them. In this work, a combination of molecular dynamics, targeted mutagenesis, fluorescent Ca2+ imaging and patch-clamp electrophysiology has been applied to G153S mutant muscle nAChR to investigate the role of hydrogen bonds formed by Ser 153 with C-loop residues near the acetylcholine-binding site. Introduction of L199T mutation to the C-loop in the vicinity of Ser 153 changed hydrogen bonds distribution, decreased acetylcholine potency (EC50 2607 vs. 146 nM) of the double mutant and decay kinetics of acetylcholine-evoked cytoplasmic Ca2+ rise (τ 14.2 ± 0.3 vs. 34.0 ± 0.4 s). These results shed light on molecular mechanisms of nAChR activation-desensitization and on the involvement of such mechanisms in channelopathy genesis.

Slow-Channel Congenital Myasthenic Syndrome due to a Novel Mutation in the Acetylcholine Receptor Alpha Subunit in a South Asian: A Case Report

Congenital myasthenic syndromes (CMS) result from genetic mutations that cause aberrations in structure and/or function of proteins involved in neuromuscular transmission. The slow-channel CMS (SCCMS) is an autosomal dominant postsynaptic defect caused by mutations in genes encoding alpha, beta, delta, or epsilon subunits of the acetylcholine receptor resulting in a functional defect which is an increase of the opening time of the receptor. We report a case of SCCMS due to a heterozygous mutation in the M2 domain of the AChR alpha subunit - CHRNA1:ENST00000348749.6:exon7:c.806T>G:p.Val269Gly and corresponding kinetic defect. A substitution of valine with phenylalanine in the same position has been previously described. This is the first reported case of a new CHRNA1 variant in a patient with SCCMS from South Asia. We also highlight the phenotype that would favour a genetic basis over an autoimmune one, in an adult presenting with fatigable weakness.

DIVULGAÇÃO CIENTÍFICA E CTS: UM ESTUDO A PARTIR DE VÍDEOS DO YOUTUBE SOBRE TEMÁTICA AMBIENTAL

This research aimed to analyze the articulations between Science, Technology and Society in Youtube videos, which approached environmental issues. The videos were chosen from channels that called themselves scientific dissemination, and that owned the ScienceVlogs "seal of quality". It were selected the Pirula Channel, the Slow Channel and Common Point, due they exhibited Nature Sciences information and they had videos about environmental impacts. From the video selection were carried out two analysis. The first one was a mapping of the number of views, of the number of subscribers and also about some features of these channels, such as language, target audience and environmental theme. The second analysis verified how the features of Science, Technology and Society appeared in each of the videos. The Science category was divided in three clusters: Interdisciplinar, Science’s Nature and Content-focused. It was realized the videos approach were mostly content-focused. There were few interdisciplinary videos. In Science’s Nature cluster there were scientific work features and some science point of views, mainly from the authors themselves. In the Technology category, two groups were created: Apparatus and Development. It was verified technology’s features related with the use of them as a tool or their development over time. The both ways were used to exemplify certain content. Only two videos were about features related with our referential about non-neutrality of technology. In the Society category were created three groups: Politics, Economy and Articulation with daily life, which were relevant features to CTS research, since it can contribute to the development of autonomy in individuals.

Determinants of the repetitive-CMAP occurrence and therapy efficacy in slow-channel myasthenia

ObjectiveTo find determinants of the occurrence of repetitive compound muscle action potential (R-CMAP) and to assess the efficacy of channel blocker therapy in slow-channel congenital myasthenic syndrome (SCCMS).MethodsNeurologic examination, EMG study, laboratory test, muscle biopsy, and next-generation and Sanger sequencing; literature review of reported patients with SCCMS, including EMG, kinetics of mutant acetylcholine receptors (AChRs), and response to therapy; and simulation of the decay phase of endplate potential (EPP) were performed.ResultsThree newly characterized and 57 reported patients with SCCMS with mutations of AChR subunits were included. In patients with R-CMAP, the length of channel opening bursts of mutant AChR was increased 8.68 ± 2.82 (mean ± SD)-fold compared to wild-type; in patients without R-CMAP, the length was increased 3.84 ± 0.65-fold (95% confidence interval 3.18–6.50, p = 0.000014). The EPP amplitude after refractory period of action potential in muscle fiber is above the threshold in patients with R-CMAP but below the threshold in patients without R-CMAP. In patients with good results from channel blocker therapy, treatment was initiated 11.60 ± 5.17 years after onset of symptoms; in patients with no to moderate benefit from channel blocker therapy, treatment was initiated 30.70 ± 12.72 years after onset (95% confidence interval −28.57 to −9.63, p = 0.00089).ConclusionsIn SCCMS, the R-CMAP occurrence is related to the extent of prolongation of the opening episodes of mutant AChR channel. Channel blocker treatment is more effective the sooner it is started after the onset of symptoms.Classification of evidenceThis study provides Class IV evidence that channel blocker therapy in patients with SCCMS improves symptoms.

Utility of Rapid Exome Sequencing in the Diagnosis of a Rare Congenital Myasthenic Syndromes in a Preterm Infant

Congenital myasthenic syndromes (CMS) are rare and challenging diagnoses in preterm neonates. We presented in this case report a preterm infant with recurrent extubation failures. An exhaustive workup to rule out common etiologies of chronic ventilator dependence was negative including a neostigmine trial, acetylcholine receptor antibodies, and chromosomal microarray. Electromyography (EMG) showed features of a neuromuscular junction defect. After ruling out metabolic, inflammatory, and immune mediated causes, a rapid exome sequencing demonstrated CHRNB1 gene mutation diagnostic of autosomal dominant slow channel CMS. The patient was started on fluoxetine and nebulized salbutamol with a gradual improvement in her respiratory function over time with minimal ventilator support.