Identification and Functional Characterization of CLCN1 Mutations Found in Nondystrophic Myotonia Patients.
Mutations in the gene coding for the skeletal muscle Cl(-) channel (CLCN1) lead to dominant or recessive myotonia. Here, we identified and characterized CLCN1 mutations in Costa Rican patients, who had been clinically diagnosed with myotonic dystrophy type 1 but who were negative for DM1 mutations. CLCN1 mutations c.501C>G, p.F167L and c.1235A>C, p.Q412P appeared to have recessive inheritance but patients had atypical clinical phenotypes; c.313C>T, p.R105C was found in combination with c.501C>G, p.F167L in an apparently recessive family and the c.461A>G, p.Q154R variant was associated with a less clear clinical picture. In Xenopus oocytes, none of the mutations exhibited alterations of fast or slow gating parameters or single channel conductance, and mutations p.R105C, p.Q154R, and p.F167L were indistinguishable from wild-type (WT). p.Q412P displayed a dramatically reduced current density, surface expression and exerted no dominant negative effect in the context of the homodimeric channel. Fluorescently tagged constructs revealed that p.Q412P is expressed inefficiently. Our study confirms p.F167L and p.R105C as myotonia mutations in the Costa Rican population, whereas p.Q154R may be a benign variant. p.Q412P most likely induces a severe folding defect, explaining the lack of dominance in patients and expression systems, but has WT properties once expressed in the plasma membrane.
Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José, Costa Rica.
Rebeca
R
Vindas-Smith
Istituto di Biofisica, CNR, Via De Marini 6, Genova, Italy.
Michele
M
Fiore
Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José, Costa Rica.|Centro de Investigación en Neurociencias (CIN), Universidad de Costa Rica, San José, Costa Rica.
Melissa
M
Vásquez
Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José, Costa Rica.|Centro de Investigación en Neurociencias (CIN), Universidad de Costa Rica, San José, Costa Rica.|Escuela de Medicina, Universidad de Costa Rica, Curridabat, San José, Costa Rica.
Patricia
P
Cuenca
Laboratorio de Neurofisiología (Neurolab), Curridabat, San José, Costa Rica.
Gerardo
G
Del Valle
Istituto di Biofisica, CNR, Via De Marini 6, Genova, Italy.
Laura
L
Lagostena
Departament de Ciències Fisiològiques II, Unitat de Fisiologia, Universitat de Barcelona, Carrer Feixa Llarga s/n, L'Hospitalet de Llobregat, Barcelona, Spain.|U-750, Centro de Investigación en red de enfermedades raras (CIBERER), ISCIII, Barcelona, Spain.
Héctor
H
Gaitán-Peñas
Departament de Ciències Fisiològiques II, Unitat de Fisiologia, Universitat de Barcelona, Carrer Feixa Llarga s/n, L'Hospitalet de Llobregat, Barcelona, Spain.|U-750, Centro de Investigación en red de enfermedades raras (CIBERER), ISCIII, Barcelona, Spain.
Raúl
R
Estevez
Istituto di Biofisica, CNR, Via De Marini 6, Genova, Italy.
Michael
M
Pusch
Instituto de Investigaciones en Salud (INISA), Universidad de Costa Rica, San José, Costa Rica.|Centro de Investigación en Neurociencias (CIN), Universidad de Costa Rica, San José, Costa Rica.|Escuela de Medicina, Universidad de Costa Rica, Curridabat, San José, Costa Rica.
Fernando
F
Morales
D000200:Action Potentials; D000483:Alleles; D000818:Animals; D018118:Chloride Channels / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D056726:Genetic Association Studies; D006801:Humans; D008297:Male; D009154:Mutation; D009222:Myotonia / Q000175:diagnosis* / Q000235:genetics* / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D010375:Pedigree; D010641:Phenotype; D017422:Sequence Analysis, DNA
C086321:CLC-1 channel; D018118:Chloride Channels
dominant-negative; electrophysiology; myotonia; protein folding; surface expression