New mutation of the Na channel in the severe form of potassium-aggravated myotonia

Muscle Nerve. 2009 May;39(5):666-73. doi: 10.1002/mus.21155.

Abstract

Myotonia manifests in several hereditary diseases, including hyperkalemic periodic paralysis (HyperPP), paramyotonia congenita (PMC), and potassium-aggravated myotonia (PAM). These are allelic disorders originating from missense mutations in the gene that codes the skeletal muscle sodium channel, Nav1.4. Moreover, a severe form of PAM has been designated as myotonia permanens. A new mutation of Nav1.4, Q1633E, was identified in a Japanese family presenting with the PAM phenotype. The proband suffered from cyanotic attacks during infancy. The mutated amino acid residue is located on the EF-hand calcium-binding motif in the intracellular C-terminus. A functional analysis of the mutant channel using the voltage-clamp method revealed disruption of fast inactivation, a slower rate of current decay, and a depolarized shift in the voltage dependence of availability. This study has identified a new mutation of PAM with a severe phenotype and emphasizes the importance of the C-terminus for fast inactivation of the sodium channel. Muscle Nerve 39: 666-673, 2009.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / metabolism
  • Adult
  • Biophysics
  • Cell Line, Transformed
  • Child
  • DNA Mutational Analysis / methods
  • Electric Stimulation / methods
  • Electromyography / methods
  • Family Health*
  • Female
  • Glutamic Acid / genetics
  • Glutamine / genetics
  • Humans
  • Ion Channel Gating / genetics
  • Japan / ethnology
  • Male
  • Membrane Potentials / drug effects
  • Membrane Potentials / genetics
  • Middle Aged
  • Models, Molecular
  • Muscle Proteins / genetics*
  • Muscle Proteins / metabolism
  • Muscle, Skeletal / metabolism
  • Muscle, Skeletal / physiopathology
  • Mutagenesis, Site-Directed / methods
  • Mutation, Missense / genetics*
  • Myotonic Disorders / genetics*
  • Myotonic Disorders / pathology
  • Myotonic Disorders / physiopathology
  • NAV1.4 Voltage-Gated Sodium Channel
  • Patch-Clamp Techniques
  • Sodium Channels / genetics*
  • Sodium Channels / metabolism
  • Transfection

Substances

  • Muscle Proteins
  • NAV1.4 Voltage-Gated Sodium Channel
  • SCN4A protein, human
  • Sodium Channels
  • Glutamine
  • Glutamic Acid
  • Adenosine Triphosphatases