Mouse Model of Fast-Channel Genetic Myasthenic Syndrome Carrying Chrne p.P141L Mutation.

Fast-channel genetic myasthenic syndromes (FCGMSs) are caused by genetic variants in muscle nicotinic acetylcholine receptor (AChR) subunits that reduce channel open times and impair neuromuscular transmission. Among these, the CHRNE p.P141L variant (εP141L) is associated with particularly severe disease. Here, we characterized a knock-in mouse model harboring the homologous p.P141L variant in Chrne (εP141L)-C57BL/6J-Chrneem1H/H made by the MRC GEMM program. Homozygous mutant mice fail to thrive, with early lethality (median survival of 16 days), closely recapitulating the severity observed in patients. Despite a preserved neuromuscular junction (NMJ) morphology and robust AChR expression, electrophysiological analyses revealed marked reductions in miniature and evoked endplate potential amplitudes and areas, accompanied by prolonged depolarization kinetics (contrary to expectations for AChR with reduced open times) and increased quantal content, indicative of impaired post-synaptic function with compensatory pre-synaptic adaptation. Notably, disease severity exceeded that of Chrne null mice, likely through competition with more functional g-subunit-containing fetal AChRs. Consistent with this, crossing εP141L mice with CHRNG-expressing mice provided little survival benefit. These findings demonstrate that dysfunctional AChR incorporation is more deleterious than receptor absence and highlight the critical role of subunit composition in sustaining neuromuscular transmission. Pharmacological enhancement of pre-synaptic release with 3,4-diaminopyridine partially improved synaptic parameters. In addition, the AChR-positive allosteric modulator DC-98 modestly improved neurotransmission. Thus, this mouse model provides a faithful platform for mechanistic studies and therapeutic development in FCGMS.