title: Genetic influences on Chronic Obstructive Pulmonary Disease - a twin study.
abstract: BACKGROUND
  Genes that contribute to the risk of developing Chronic Obstructive Pulmonary Disease (COPD) have been identified, but an attempt to accurately quantify the total genetic contribution to COPD has to our knowledge never been conducted.
  
  
  METHODS
  Hospital discharge diagnoses data on COPD were analysed in 22,422 Danish twin pairs, 20-71 years of age. The analyses were replicated in a population of 27,668 Swedish twin pairs, 45-108 years of age. A Cox-regression model was applied to the discordant time from the age at first hospital admission for COPD in the co-twin of an affected twin. Latent factor models were used to estimate genetic and environmental effects.
  
  
  RESULTS
  The probandwise concordance rate for COPD was higher in monozygotic (MZ) than in dizygotic (DZ) twins, 0.19 vs. 0.07 (p = 0.08) in the Danish population, and 0.20 vs. 0.08 (p = 0.006) in the Swedish population. After adjusting for sex, smoking and age at first hospital admission the risk of developing COPD in the co-twin of an affected twin was higher in MZ than in DZ twins, with hazards ratio 4.3 (95% confidence interval 1.2-15.8, p = 0.03) in Danish twins and 3.4 (1.5-7.7, p = 0.004) in Swedish twins. According to the most parsimonious model, additive genetic factors explained 63% (46-77%) of the individual COPD-susceptibility in the Danish population and 61% (48-72%) in the Swedish population.
  
  
  CONCLUSIONS
  The susceptibility to develop severe COPD, as defined by hospitalizations, is strongly influenced by genetic factors. Approximately 60% of the individual susceptibility can be explained by genetic factors.
authors.affiliation: Department of Respiratory Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, Copenhagen, Denmark. trulsingebrigtsen@gmail.com
authors.forename: Truls
authors.initials: T
authors.lastname: Ingebrigtsen
authors.forename: Simon F
authors.initials: SF
authors.lastname: Thomsen
authors.forename: Jørgen
authors.initials: J
authors.lastname: Vestbo
authors.forename: Sophie
authors.initials: S
authors.lastname: van der Sluis
authors.forename: Kirsten O
authors.initials: KO
authors.lastname: Kyvik
authors.forename: Edwin K
authors.initials: EK
authors.lastname: Silverman
authors.forename: Magnus
authors.initials: M
authors.lastname: Svartengren
authors.forename: Vibeke
authors.initials: V
authors.lastname: Backer
mesh_terms: D000328:Adult; D000368:Aged; D003718:Denmark; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000235:genetics*; D012042:Registries; D012907:Smoking / Q000235:genetics; D013548:Sweden; D014427:Twins / Q000235:genetics; D055815:Young Adult