CLCN1 Mutations in Czech Patients with Myotonia Congenita, In Silico Analysis of Novel and Known Mutations in the Human Dimeric Skeletal Muscle Chloride Channel

Abstract

Myotonia congenita (MC) is a genetic disease caused by mutations in the skeletal muscle chloride channel gene (CLCN1) encoding the skeletal muscle chloride channel (ClC-1). Mutations of CLCN1 result in either autosomal dominant MC (Thomsen disease) or autosomal recessive MC (Becker disease). The ClC-1 protein is a homodimer with a separate ion pore within each monomer. Mutations causing recessive myotonia most likely affect properties of only the mutant monomer in the heterodimer, leaving the wild type monomer unaffected, while mutations causing dominant myotonia affect properties of both subunits in the heterodimer. Our study addresses two points: 1) molecular genetic diagnostics of MC by analysis of the CLCN1 gene and 2) structural analysis of mutations in the homology model of the human dimeric ClC-1 protein. In the first part, 34 different types of CLCN1 mutations were identified in 51 MC probands (14 mutations were new). In the second part, on the basis of the homology model we identified the amino acids which forming the dimer interface and those which form the Cl- ion pathway. In the literature, we searched for mutations of these amino acids for which functional analyses were performed to assess the correlation between localisation of a mutation and occurrence of a dominant-negative effect (corresponding to dominant MC). This revealed that both types of mutations, with and without a dominant-negative effect, are localised at the dimer interface while solely mutations without a dominant-negative effect occur inside the chloride channel. This work is complemented by structural analysis of the homology model which provides elucidation of the effects of mutations, including a description of impacts of newly detected missense mutations.

CLCN1 Myotonia congenita mutation with a variable pattern of inheritance suggests a novel mechanism of dominant myotonia

“…We have identified the p.A493E mutation in a family with dominant myotonia. Of interest, this mutation was found previously in a patient with recessive myotonia . We conclude that the p.A493E mutation can be found in both dominant and recessive pedigrees, as can the previously reported missense mutations G230E and A531V, and the deletion R894X .…”

The analysis of myotonia congenita mutations discloses functional clusters of amino acids within the CBS2 domain and the C-terminal peptide of the ClC-1 channel

“…Two related patients were found to carry the c.2551G>A (p.Val851Met) mutation in combination with c.86A>C (p.His29Pro) on the same chromosome. This latter mutation was previously found in association with p.Tyr257X and p.Ala566Val in another patient reporting moderate myotonia, permanent limb‐girdle muscle weakness, and scoliosis (Skálová et al., ). The proband is a woman, now 50 years old, who presented with lower‐limb muscle weakness, stiffness with difficulty to start movements, and painful myotonia and warm‐up.…”

ClC‐1 mutations in myotonia congenita patients: insights into molecular gating mechanisms and genotype–phenotype correlation

“…; Skalova et al . ). Most dominant MC mutations proven to cause a dominant‐negative effect when co‐expressed with WT subunits effectively reside at the boundary region between two monomers or in its proximity.…”

“…Conversely, mutations occurring in the channel pore show no dominant‐negative effect and can cause the disease by other mechanisms (Skalova et al . ).…”

“…Interestingly, the L198P mutation is located in helix D, which forms part of the ion conductive pore and is known to interact with helices H, R and the CBS2 domain, notably being involved in the mechanism of slow gating (Bennetts & Parker, ; Skalova et al . ). Two other substitutions have been found at the same conserved position in myotonic patients (Simpson et al .…”