Dominant mutations in Nav1.4, encoded by SCN4A gene (NC_000017.11) can lead to Hyper-, Hypo- or Normo- kalemic Periodic Paralysis (OMIM 170500) or to different forms of myotonia [Paramyotonia Congenita (PMC): OMIM 168300; Sodium Channel Myotonia (SCM): OMIM 603967]; Severe neonatal episodic laryngospasm (SNEL): OMIM 608390, whereas recessive mutations are associated to congenital myopathy or congenital myasthenic syndromes (OMIM 614198). The gene discussed is SCN4A; the disease is congenital myopathy.