G.P.99 Molecular genetic diagnostics of myotonia congenita and analysis of the effects of mutations in the CLCN1 gene on the structure of the dimeric ClC1 chloride channel

Abstract

Abstract Non-dystrophic myotonias are a group of skeletal muscle disorders associated with mutations in the CLCN1 and SCN4A genes. Mutations of CLCN1 result in either autosomal dominant (Thomsen) or autosomal recessive (Becker) myotonia congenita (MC). A subset of CLCN1 mutations have been found to cause both recessive and dominant myotonias, while mutations in the SCN4A gene are typically inherited as an autosomal dominant trait. The ClC1 protein is a homodimer with a separate ion pore within each monomer, and the varied inheritance pattern of myotonias appears to result from differential effects of a mutation on the channel dimer. Mutations causing recessive myotonia most likely affect properties of a mutant monomer, leaving the wild type monomer unaffected in the heterodimer, and on the other hand mutations causing dominant myotonia affect properties of both subunits in the wild type/mutant heterodimer. Our study addresses two points: (1) molecular genetic diagnostics of MC by tandem analysis of the CLCN1 and SCN4A genes and (2) homology modelling of the molecular structure of the dimeric ClC1 channel. In the first part, mutations associated with the disease were identified in 57 probands, 39 carrying mutations in CLCN1 and 18 in SCN4A. In the second part, we performed homology modelling of the dimeric ClC1 channel on the basis of known crystallographic structures. From this model, we predicted the aminoacids (AAs) which form the dimer interface and those which form the Cl− ion pathway. Further, using our model we performed searches for mutations of AAs forming the dimer interface or/and the Cl− ion pathway in our model which have been found in patients with MC to assess the correlation between the localisation of a mutation and the type of MC. This work was funded by the project “CEITEC – Central European Institute of Technology” (CZ.1.05/1.1.00/02.0068).