p.Asn1180Ile mutation of SCN4A gene in an Italian family with myopathy and myotonic syndrome.

Introduction: Mutations of the skeletal muscle sodium channel gene SCN4A are associated with several neuromuscular disorders including hyper/hypokaliemic periodic paralysis, paramyotonia congenita and sodium channel myotonia. These disorders are distinguished from dystrophic myotonias by the absence of progressive weakness and extramuscular systemic involvement.

Methods: We present an Italian family with 2 subjects carrying a p.Asn1180Ile mutation in SCN4A gene showing a peculiar clinical picture characterized by the association of myopathic features and myotonia.

Results: The clinical, electromyographic and histological findings of these patients are reported. The possible pathogenicity of the mutation was tested by three different software, all giving positive results.

Discussion: This is the first report of a dominant, heterozygous mutation in SCN4A causing a complex phenotype of non-congenital myopathy and myotonic syndrome. We suggest that, in patients with myotonia and myopathy not related to dystrophic myotonias, the sequence analysis of SCN4A gene should be performed.