title: Intra- and interfamily phenotypic diversity in pain syndromes associated with a gain-of-function variant of NaV1.7.
abstract: BACKGROUND
  Sodium channel NaV1.7 is preferentially expressed within dorsal root ganglia (DRG), trigeminal ganglia and sympathetic ganglion neurons and their fine-diamter axons, where it acts as a threshold channel, amplifying stimuli such as generator potentials in nociceptors. Gain-of-function mutations and variants (single amino acid substitutions) of NaV1.7 have been linked to three pain syndromes: Inherited Erythromelalgia (IEM), Paroxysmal Extreme Pain Disorder (PEPD), and Small Fiber Neuropathy (SFN). IEM is characterized clinically by burning pain and redness that is usually focused on the distal extremities, precipitated by mild warmth and relieved by cooling, and is caused by mutations that hyperpolarize activation, slow deactivation, and enhance the channel ramp response. PEPD is characterized by perirectal, periocular or perimandibular pain, often triggered by defecation or lower body stimulation, and is caused by mutations that severely impair fast-inactivation. SFN presents a clinical picture dominated by neuropathic pain and autonomic symptoms; gain-of-function variants have been reported to be present in approximately 30% of patients with biopsy-confirmed idiopathic SFN, and functional testing has shown altered fast-inactivation, slow-inactivation or resurgent current. In this paper we describe three patients who house the NaV1.7/I228M variant.
  
  
  METHODS
  We have used clinical assessment of patients, quantitative sensory testing and skin biopsy to study these patients, including two siblings in one family, in whom genomic screening demonstrated the I228M NaV1.7 variant. Electrophysiology (voltage-clamp and current-clamp) was used to test functional effects of the variant channel.
  
  
  RESULTS
  We report three different clinical presentations of the I228M NaV1.7 variant: presentation with severe facial pain, presentation with distal (feet, hands) pain, and presentation with scalp discomfort in three patients housing this NaV1.7 variant, two of which are from a single family. We also demonstrate that the NaV1.7/I228M variant impairs slow-inactivation, and produces hyperexcitability in both trigeminal ganglion and DRG neurons.
  
  
  CONCLUSIONS
  Our results demonstrate intra- and interfamily phenotypic diversity in pain syndromes produced by a gain-of-function variant of NaV1.7.
authors.affiliation: Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Estacion
authors.forename: Chongyang
authors.initials: C
authors.lastname: Han
authors.forename: Jin-Sung
authors.initials: JS
authors.lastname: Choi
authors.forename: Janneke G J
authors.initials: JG
authors.lastname: Hoeijmakers
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Lauria
authors.forename: Joost P H
authors.initials: JP
authors.lastname: Drenth
authors.forename: Monique M
authors.initials: MM
authors.lastname: Gerrits
authors.forename: Sulayman D
authors.initials: SD
authors.lastname: Dib-Hajj
authors.forename: Catharina G
authors.initials: CG
authors.lastname: Faber
authors.forename: Ingemar S J
authors.initials: IS
authors.lastname: Merkies
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Waxman
mesh_terms: D000595:Amino Acid Sequence; D005260:Female; D005727:Ganglia, Spinal / Q000378:metabolism; D014644:Genetic Variation; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009154:Mutation; D062556:NAV1.7 Voltage-Gated Sodium Channel; D009474:Neurons / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010641:Phenotype; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism; D013001:Somatoform Disorders / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
chemical_list: D062556:NAV1.7 Voltage-Gated Sodium Channel; C486866:SCN9A protein, human; D015222:Sodium Channels