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SCN4A mutation as modifying factor of myotonic dystrophy type 2 phenotype
E Bugiardini1, I Rivolta2, A Binda2
1Department of Biomedical Sciences for Health, IRCCS Policlinico San Donato, University of Milan, Italy.
Neuromuscular Disorders : NMD
|February 10, 2015
Summary
Myotonic dystrophy type 2 (DM2) patients with severe myotonia may have co-occurring sodium channel gene (SCN4A) mutations. This novel SCN4A variant potentially worsens DM2 symptoms, suggesting broader genetic screening for myotonic disorders.
Area of Science:
- Neurology
- Genetics
- Molecular Biology
Background:
- Myotonic dystrophy type 2 (DM2) is typically associated with chloride channel (CLCN1) mutations.
- Sodium channel gene (SCN4A) mutations have not been previously described in DM2 patients.
Observation:
- A 26-year-old patient presented with severe, early-onset myotonia, characteristic of DM2.
- Genetic analysis revealed both DM2 and a novel SCN4A missense mutation (c.215C>T, p.Pro72Leu).
Findings:
- The novel SCN4A mutation affects the Nav1.4 channel's cytoplasmic N-terminus.
- Electrophysiological studies showed the P72L variant shifts activation voltage dependence, potentially increasing cellular excitability.
Implications:
- SCN4A mutations may exacerbate the myotonic phenotype in DM2.
- Screening for SCN4A mutations is recommended for DM2 patients with severe or atypical myotonia.
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