title: Focal and abnormally persistent paralysis associated with congenital paramyotonia.
abstract: Mutations of the skeletal muscle voltage-gated sodium channel (NaV1.4) are an established cause of several clinically distinct forms of periodic paralysis and myotonia. Focal paresis has sometimes already been described. We report a case with atypical clinical manifestation comprising paramyotonia and cold-induced persistent and focal paralysis. A 27-year-old woman presented with paramyotonia congenita since her childhood. She experienced during her childhood one brief episode of generalised weakness. At the age of 27, she experienced a focal paresis lasting for several months. The known mutation p.Val1293Ile was found in the muscle sodium channel gene (SCN4A). Channel inactivation is involved in most Na(+) channelopathies. Fast inactivation is known to be responsible for the myotonia phenotype. We hypothesise that the V1293I mutation may also alter the slow inactivation in specific conditions, for example, prolonged cold exposure or prolonged and intensive exercise. This observation broadens the spectrum of clinical manifestations of this sodium channel mutation.
authors.affiliation: Centre de Référence Maladies Neuromusculaires Nantes-Angers, Nantes, France.
authors.forename: Armelle
authors.initials: A
authors.lastname: Magot
authors.affiliation: Service de génétique médicale, Nantes, France.
authors.forename: Albert
authors.initials: A
authors.lastname: David
authors.affiliation: Centre de Référence des Canalopathies Musculaires, Service de Biochimie Métabolique, ICM UMR_S975, Paris, France.
authors.forename: Damien
authors.initials: D
authors.lastname: Sternberg
authors.affiliation: Centre de Référence Maladies Neuromusculaires Nantes-Angers, Nantes, France.
authors.forename: Yann
authors.initials: Y
authors.lastname: Péréon
mesh_terms: D005260:Female; D006801:Humans; D008801:Mexiletine / Q000627:therapeutic use; D009154:Mutation / Q000235:genetics; D009224:Myotonia Congenita / Q000150:complications* / Q000188:drug therapy / Q000235:genetics; D062553:NAV1.4 Voltage-Gated Sodium Channel / Q000235:genetics; D010243:Paralysis / Q000188:drug therapy / Q000209:etiology*; D016896:Treatment Outcome; D061567:Voltage-Gated Sodium Channel Blockers / Q000627:therapeutic use; D055815:Young Adult
chemical_list: D062553:NAV1.4 Voltage-Gated Sodium Channel; D061567:Voltage-Gated Sodium Channel Blockers; D008801:Mexiletine