title: Longitudinal concordance for clinical characteristics in a Swedish-Danish twin population with inflammatory bowel disease.
abstract: BACKGROUND
  The genetic influence on disease course in inflammatory bowel disease (IBD) remains unknown. We therefore aimed to study longitudinal concordance for clinical characteristics and longitudinal stability using the Montreal Classification in an IBD twin population.
  
  
  METHODS
  A total of 158 twins with ulcerative colitis (UC) (18 belonging to 9 concordant monozygotic pairs) and 141 twins with Crohn's disease (CD) (34 belonging to 17 concordant monozygotic pairs) were enrolled. Medical notes were scrutinized for clinical characteristics at diagnosis and after 10 years. Using the binominal distribution, we tested the hypothesis that clinical characteristics were independent within individuals in disease concordant monozygotic pairs.
  
  
  RESULTS
  In CD, location was identical in 11/17 monozygotic concordant pairs at diagnosis (P = 0.008) and in 11/16 pairs after 10 years (P = 0.02). Behavior at diagnosis was identical in 13/17 pairs (P = 0.03) and in 11/16 pairs after 10 years (P = 0.01). Monozygotic UC twins were concordant (within 5 years) for age at diagnosis (6/9 pairs; P < 0.001) and symptomatic onset (4/9 pairs; P = 0.02) but not for extent of disease at diagnosis or after 10 years. The Montreal Classification did not demonstrate longitudinal stability, either regarding location or behavior of CD or extent of UC.
  
  
  CONCLUSIONS
  The high phenotypic concordance, both at diagnosis and longitudinally, in monozygotic twins with CD supports a genetic influence not only on disease occurrence but also on disease course. This contrasts with UC, where the genetic impact appears less. Montreal Classification characteristics changed over time and should be used cautiously.
authors.affiliation: Department of Internal Medicine, Orebro University Hospital, Orebro, Sweden. jonas.halfvarson@orebroll.se
authors.forename: Jonas
authors.initials: J
authors.lastname: Halfvarson
authors.forename: Tine
authors.initials: T
authors.lastname: Jess
authors.forename: Lennart
authors.initials: L
authors.lastname: Bodin
authors.forename: Gunnar
authors.initials: G
authors.lastname: Järnerot
authors.forename: Pia
authors.initials: P
authors.lastname: Munkholm
authors.forename: Vibeke
authors.initials: V
authors.lastname: Binder
authors.forename: Curt
authors.initials: C
authors.lastname: Tysk
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003093:Colitis, Ulcerative / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology*; D003424:Crohn Disease / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology*; D003718:Denmark; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D013548:Sweden; D013997:Time Factors; D014427:Twins