Emergence of lingual dystonia and strabismus in early-onset SCN8A self-limiting familial infantile epilepsy

Epileptic Disord. 2024 Apr;26(2):219-224. doi: 10.1002/epd2.20203. Epub 2024 Mar 4.

Abstract

Pathogenic variants in SCN8A are associated with a broad phenotypic spectrum, including Self-Limiting Familial Infantile Epilepsy (SeLFIE), characterized by infancy-onset age-related seizures with normal development and cognition. Movement disorders, particularly paroxysmal kinesigenic dyskinesia typically arising after puberty, may represent another core symptom. We present the case of a 1-year-old girl with a familial disposition to self-limiting focal seizures from the maternal side and early-onset orofacial movement disorders associated with SCN8A-SeLFIE. Brain MRI was normal. Genetic testing revealed a maternally inherited SCN8A variant [c.4447G > A; p.(Glu1483Lys)]. After the introduction of valproic acid, she promptly achieved seizure control as well as complete remission of strabismus and a significant decrease in episodes of tongue deviation. Family history, genetic findings, and epilepsy phenotype are consistent with SCN8A-SeLFIE. Movement disorders are an important part of the SCN8A phenotypic spectrum, and this case highlights the novel early-onset orofacial movement disorders associated with this condition. The episodes of tongue deviation and protrusion suggest focal oromandibular (lingual) dystonia. Additionally, while infantile strabismus or esophoria is a common finding in healthy individuals, our case raises the possibility of an ictal origin of the strabismus. This study underscores the importance of recognizing and addressing movement disorders in SCN8A-SeLFIE patients, particularly the rare early-onset orofacial manifestations. It adds to the growing body of knowledge regarding the diverse clinical presentations of SCN8A-associated disorders and suggests potential avenues for clinical management and further research.

Keywords: SCN8A; intermittent esotropia; lingual dyskinesia; movement disorders; paroxysmal strabismus; self‐limiting familial infantile epilepsy.

Publication types

  • Case Reports

MeSH terms

  • Dystonia* / genetics
  • Dystonic Disorders* / genetics
  • Epilepsy* / diagnosis
  • Epileptic Syndromes* / genetics
  • Female
  • Humans
  • Infant
  • Movement Disorders*
  • Mutation
  • NAV1.6 Voltage-Gated Sodium Channel / genetics
  • Seizures / genetics
  • Strabismus* / genetics

Substances

  • NAV1.6 Voltage-Gated Sodium Channel
  • SCN8A protein, human