A novel mutation in SCN4A causes severe myotonia and school-age-onset paralytic episodes

Harumi Yoshinaga, Shunichi Sakoda, Jean Marc Good, Masanori P. Takahashi, Tomoya Kubota, Eri Arikawa-Hirasawa, Tomohiko Nakata, Kinji Ohno, Tetsuro Kitamura, Katsuhiro Kobayashi, Yoko Ohtsuka

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


Mutations in the pore-forming subunit of the skeletal muscle sodium channel (SCN4A) are responsible for hyperkalemic periodic paralysis, paramyotonia congenita and sodium channel myotonia. These disorders are classified based on their cardinal symptoms, myotonia and/or paralysis. We report the case of a Japanese boy with a novel mutation of SCN4A, p.I693L, who exhibited severe episodic myotonia from infancy and later onset mild paralytic attack. He started to have apneic episodes with generalized hypertonia at age of 11 months, then developed severe episodic myotonia since 2 years of age. He presented characteristic generalized features which resembled Schwarz-Jampel syndrome. After 7 years old, paralytic episodes occurred several times a year. The compound muscle action potential did not change during short and long exercise tests. Functional analysis of the mutant channel expressed in cultured cell revealed enhancement of the activation and disruption of the slow inactivation, which were consistent with myotonia and paralytic attack. The severe clinical features in his infancy may correspond to myotonia permanence, however, he subsequently experienced paralytic attacks. This case provides an example of the complexity and overlap of the clinical features of sodium channel myotonic disorders.

Original languageEnglish
Pages (from-to)15-19
Number of pages5
JournalJournal of the neurological sciences
Issue number1-2
Publication statusPublished - Apr 15 2012


  • Activation
  • Channelopathy
  • Na channel
  • SCN4A
  • Schwarz-Jampel syndrome
  • Skeletal muscle
  • Slow inactivation

ASJC Scopus subject areas

  • Neurology
  • Clinical Neurology


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