Functional and Structural Characterization of ClC-1 and Nav1.4 Channels Resulting from CLCN1 and SCN4A Mutations Identified Alone and Coexisting in Myotonic Patients.
Non-dystrophic myotonias have been linked to loss-of-function mutations in the ClC-1
chloride channel or gain-of-function mutations in the Nav1.4 sodium channel. Here, we describe
a family with members diagnosed with Thomsen’s disease. One novel mutation (p.W322*) in
CLCN1 and one undescribed mutation (p.R1463H) in SCN4A are segregating in this family. The
CLCN1-p.W322* was also found in an unrelated family, in compound heterozygosity with the known
CLCN1-p.G355R mutation. One reported mutation, SCN4A-p.T1313M, was found in a third family.
Both CLCN1 mutations exhibited loss-of-function: CLCN1-p.W322* probably leads to a non-viable
truncated protein; for CLCN1-p.G355R, we predict structural damage, triggering important steric
clashes. The SCN4A-p.R1463H produced a positive shift in the steady-state inactivation increasing
window currents and a faster recovery from inactivation. These gain-of-function effects are probably
due to a disruption of interaction R1463-D1356, which destabilizes the voltage sensor domain (VSD)
IV and increases the flexibility of the S4-S5 linker. Finally, modelling suggested that the p.T1313M
induces a strong decrease in protein flexibility on the III-IV linker. This study demonstrates that
CLCN1-p.W322* and SCN4A-p.R1463H mutations can act alone or in combination as inducers of
myotonia. Their co-segregation highlights the necessity for carrying out deep genetic analysis to
provide accurate genetic counseling and management of patients.Universidad de Costa Rica/[]/UCR/Costa RicaFondazione AIRC per la Ricerca sul Cancro/[IG 21558]/AIRC/ItaliaItalian Research Ministry/[PRIN 20174TB8KW]//ItaliaUCR::Vicerrectoría de Docencia::Salud::Facultad de Medicina::Escuela de MedicinaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Centro de Investigación en Neurociencias (CIN)UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto de Investigaciones en Salud (INISA)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí