Decoding Pathogenesis of Slow-Channel Congenital Myasthenic Syndromes using Recombinant Expression and Mice Models

Abstract

Despite the fact that they are orphan diseases, congenital myasthenic syndromes (CMS) challenge those who suffer from it by causing fatigable muscle weakness, in the most benign cases, to a progressive wasting of muscles that may sentence patients to a wheelchair or even death. Compared to other more common neurological diseases, CMS are rare. Nevertheless, extensive research in CMS is performed in laboratories such as ours. Among the diverse neuromuscular disorders of CMS, we are focusing in the slow-channel congenital myasthenic syndrome (SCS), which is caused by mutations in genes encoding acetylcholine receptor subunits. The study of SCS has evolved from clinical electrophysiological studies to in vitro expression systems and transgenic mice models. The present review evaluates the methodological approaches that are most commonly employed to assess synaptic impairment in SCS and also provides perspectives for new approaches. Electrophysiological methodologies typically employed by physicians to diagnose patients include electromyography, whereas patient muscle samples are used for intracellular recordings, single-channel recordings and toxin binding experiments. In vitro expression systems allow the study of a particular mutation without the need of patient intervention. Indeed, in vitro expression systems have usually been implicated in the development of therapeutic strategies such as quinidine- and fluoxetine-based treatments and, more recently, RNA interference. A breakthrough in the study of SCS has been the development of transgenic mice bearing the mutations that cause SCS. These transgenic mice models have actually been key in the elucidation of the pathogenesis of the SCS mutations by linking IP-3 receptors to calcium overloading, as well as caspases and calpains to the hallmark of SCS, namely endplate myopathy. Finally, we summarize our experiences with suspected SCS patients from a local perspective and comment on one aspect of the contribution of our group in the study of SCS.