title: Evidence for genetic factors in vasovagal syncope: a twin-family study.
abstract: OBJECTIVE
  Vasovagal syncope (VVS) is the most frequent type of syncope and a common differential diagnosis of epilepsy. The role of genetic factors in VVS is debated. We performed a twin-family study to clarify this question and to analyze the putative mode of inheritance.
  
  
  METHODS
  Fifty-one same-sex twin pairs where at least 1 had syncope were ascertained. The twins were interviewed via telephone using a standardized questionnaire. Available medical records were obtained. Information on the affected status of first- and second-degree relatives was acquired.
  
  
  RESULTS
  There was a trend toward higher casewise concordance in monozygous (MZ, 0.75) than dizygous (DZ, 0.50) twins for any syncope (p = 0.06). Significant and strong effects on concordance between MZ and DZ twins were found for fainting at least twice unrelated to external circumstances (0.71 vs 0.27, p = 0.018) and for syncope associated with typical vasovagal triggers (0.62 vs 0.00, p < 0.001). Twelve of 19 concordant MZ twin pairs reported sparse or no other affected family members whereas in the other 7 pairs multiple close relatives were affected.
  
  
  CONCLUSIONS
  The twin analysis provides strong evidence for the relevance of genetic factors in VVS. Analysis of the families suggests that complex inheritance (multiple genes ± environmental factors) is usual, with rarer families possibly segregating a major autosomal dominant gene.
authors.affiliation: Epilepsy Research Centre, The University of Melbourne, Austin Health, Heidelberg, Victoria, Australia.
authors.forename: Karl Martin
authors.initials: KM
authors.lastname: Klein
authors.forename: San San
authors.initials: SS
authors.lastname: Xu
authors.forename: Kate
authors.initials: K
authors.lastname: Lawrence
authors.forename: Alexandra
authors.initials: A
authors.lastname: Fischer
authors.forename: Samuel F
authors.initials: SF
authors.lastname: Berkovic
mesh_terms: D000328:Adult; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D019462:Syncope, Vasovagal / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*