Novel SCN5A mutation (Q55X) associated with age-dependent expression of Brugada syndrome presenting as neurally mediated syncope

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Makita N, Sumitomo N, Watanabe I, and Tsutsui H (2007) Novel SCN5A mutation (Q55X) associated with age-dependent expression of Brugada syndrome presenting as neurally mediated syncope. Heart Rhythm 4:4 516–9.

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Abstract: BACKGROUND: An association between Brugada syndrome and neurally mediated syncope has been described. Although mutations in SCN5A have been identified in Brugada syndrome, the genetic link between Brugada syndrome and neurally mediated syncope has not been determined. OBJECTIVES: The purpose of the study was to clinically and genetically characterize a man with recurrent syncope that originally was diagnosed as neurally mediated syncope at age 8 years but subsequently manifested as Brugada syndrome at age 17 years. METHODS: The proband underwent clinical examination, which included head-up tilt test, sodium channel provocation test, and electrophysiologic study. Genetic screening of SCN5A was performed for the proband and his family members. The biophysical properties of a mutant SCN5A channel in a heterologous expression system were studied using whole-cell, patch clamp technique. RESULTS: The proband showed positive head-up tilt test, coved-type ST elevation recorded from the third intercostal space, and positive pilsicainide provocation test. Ventricular fibrillation was inducible at programmed electrical stimulation, consistent with characteristics of both Brugada syndrome and neurally mediated syncope. A novel nonsense SCN5A mutation (Q55X) was identified in the proband, his mother, and his asymptomatic brother. The heterologously expressed mutant channel was nonfunctional. CONCLUSION: We genetically determined an SCN5A mutation in a patient showing the combined phenotype of neurally mediated syncope and Brugada syndrome. Neurally mediated syncope and Brugada syndrome may share, at least in part, a common pathophysiologic mechanism.

Keywords: Brugada syndrome, Neurally mediated syncope, SCN5A, Tilt test

Context

  • Single-case report of 17 year old male with history of first-degree heart block and syncopal episodes that often occurred during emotional stress and were thus diagnosed as neurally-mediated. Over time the presentation changed and Brugada syndrome was eventually diagnosed. The authors discuss several other reports of cases where this syncope presented as neurally-mediated or vasovagal syncope. Heart and brain pathology may be linked by a mutation in a channel expressed in both organs, by autonomic links, or both.

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