title: Familial aggregation of atrial fibrillation: a study in Danish twins.
abstract: BACKGROUND
  Heritability may play a role in nonfamilial atrial fibrillation (AF). We hypothesized that a monozygotic (MZ) twin whose co-twin was diagnosed with AF would have an increased risk of the disease compared with a dizygotic (DZ) twin in the same situation.
  
  
  RESULTS
  A sample of 1137 same-sex twin pairs (356 MZ and 781 DZ pairs) in which one or both members were diagnosed with AF were identified in The Danish Twin Registry. Concordance rates were twice as high for MZ pairs than for DZ pairs regardless of sex (22.0% versus 11.6%, P<0.0001). In a Cox regression of event-free survival times, we compared the time span between occurrences of disease in MZ and DZ twins. The unaffected twin was included when his or her twin-sibling (the index twin) was diagnosed with AF. After adjustment for age at entry, MZ twins had a significantly shorter event-free survival time (hazard ratio, 2.0; 95% CI, 1.3 to 3.0), thereby indicating a genetic component. Using biometric models, we estimated the heritability of AF to be 62% (55% to 68%), due to additive genetics. There were no significant differences across sexes.
  
  
  CONCLUSIONS
  All the analyses of twin similarities in the present study indicate that genetic factors play a substantial role in the risk of AF for both sexes. The recurrence risk for co-twins (12% to 22%) is clinically relevant and suggests that co-twins of AF-affected twins belong to a high-risk group for AF.
authors.affiliation: The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Cardiology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark.
authors.forename: Ingrid Elisabeth
authors.initials: IE
authors.lastname: Christophersen
authors.forename: Lasse Steen
authors.initials: LS
authors.lastname: Ravn
authors.forename: Esben
authors.initials: E
authors.lastname: Budtz-Joergensen
authors.forename: Axel
authors.initials: A
authors.lastname: Skytthe
authors.forename: Stig
authors.initials: S
authors.lastname: Haunsoe
authors.forename: Jesper Hastrup
authors.initials: JH
authors.lastname: Svendsen
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000453:epidemiology* / Q000235:genetics*; D001699:Biometry; D003718:Denmark / Q000453:epidemiology; D005192:Family Health; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D008957:Models, Genetic; D015995:Prevalence; D016016:Proportional Hazards Models; D012042:Registries / Q000706:statistics & numerical data; D012307:Risk Factors; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic