title: Heritability of psoriasis in a large twin sample.
abstract: BACKGROUND
  Previous twin studies have shown greater concordance rates for psoriasis in MZ than in DZ twins, and heritability estimates between 66% and 90%. This supports a genetic influence on psoriasis, but also highlights the fact that genes are not the only explanation for the disease.
  
  
  OBJECTIVE
  To study the concordance of psoriasis in a population-based twin sample.
  
  
  METHODS
  Data on psoriasis in 10 725 twin pairs, aged 20-71 years, from the Danish Twin Registry was collected via a questionnaire survey. The concordance and heritability of psoriasis were estimated.
  
  
  RESULTS
  In total, 4·1% of the men and 4·2% of the women had a lifetime history of psoriasis. The proband-wise concordance for psoriasis was larger in monozygotic than in dizygotic twins, 0·33 vs. 0·17. Genetic factors explained 68% (60-75%) of the variation in the susceptibility to psoriasis, whereas the rest of the variation was explained by nonshared environmental factors.
  
  
  CONCLUSIONS
  The results confirm that psoriasis is a complex multifactorial disease controlled by both exogenous and endogenous factors.
authors.affiliation: Department of Dermato-Allergology, Gentofte Hospital, Hellerup, Denmark. ann_sophie_l@hotmail.com
authors.forename: A S
authors.initials: AS
authors.lastname: Lønnberg
authors.forename: L
authors.initials: L
authors.lastname: Skov
authors.forename: A
authors.initials: A
authors.lastname: Skytthe
authors.forename: K O
authors.initials: KO
authors.lastname: Kyvik
authors.forename: O B
authors.initials: OB
authors.lastname: Pedersen
authors.forename: S F
authors.initials: SF
authors.lastname: Thomsen
mesh_terms: D000328:Adult; D000368:Aged; D003718:Denmark / Q000453:epidemiology; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011565:Psoriasis / Q000453:epidemiology / Q000235:genetics*; D012042:Registries; D012307:Risk Factors; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D055815:Young Adult