Multidisciplinary study of a new ClC-1 mutation causing myotonia congenita: A paradigm to understand and treat ion channelopathies

Abstract

Myotonia congenita is an inherited disease that is characterized by impaired muscle relaxation after contraction caused by loss-of-function mutations in the skeletal muscle ClC-1 channel.We report a novel ClC-1 mutation, T335N, that is associated with amild phenotype in 1patient, locatedin the extracellular I-J loop.The purpose of this study was to provide a solid correlation between T335Ndysfunction and clinical symptoms in the affected patient aswell as to offerhints fordrugdevelopment.Our multidisciplinary approachincludespatch-clampelectrophysiologyonT335Nand ClC-1wild-type channels expressed intsA201 cells,Western blot andquantitativePCRanalyses onmuscle biopsies from patient and unaffected individuals, and molecular dynamics simulations using a homology model of the ClC-1 dimer. T335N channels display reduced chloride currents as a result of gating alterations rather than altered surface expression. Molecular dynamics simulations suggest that the I-J loop might be involved in conformational changes that occur at the dimerinterface, thusaffectinggating. Finally, thegeneexpressionprofile ofT335Ncarriershowedadiverse expression of K+ channel genes, compared with control individuals, as potentially contributing to the phenotype. This experimental paradigm satisfactorily explained myotonia in the patient. Furthermore, it could be relevant to the study and therapy of any channelopathy.-Imbrici, P., Altamura, C., Camerino, G. M.,Mangiatordi, G. F., Conte, E.,Maggi, L., Brugnoni, R., Musaraj, K., Caloiero, R., Alberga, D., Marsano, R. M., Ricci, G., Siciliano, G., Nicolotti,O.,Mora, M., Bernasconi, P., Desaphy, J.-F., Mantegazza, R., Camerino, D. C. Multidisciplinary study of a new ClC-1 mutation causing myotonia congenita: a paradigm to understand and treat ion channelopathies.