Background: The varying clinical course of Crohns disease (CD) and ulcerative colitis (UC) emphasizes the need toclassify patients according to clinical characteristics. Accurate classifi cation is important regarding prognosis and stratifyingpatients with respect to therapy. Whether longitudinal changes of clinical characteristics are caused by externalfactors only, or if genetics predispose is unknown. Twin studies can be of help in this respect. The aim was to evaluatethe concordance for longitudinal changes of clinical characteristics among monozygotic twins with IBD.
Methods: Twins derived from previous known Swedish and Danish population-based cohorts. After consent, the medicalnotes were scrutinized to classify clinical characteristics, at diagnosis and after 10 years, according to the Montrealclassifi cation. Acute colectomy due to unresponsive colitis was used as a proxy marker for severe UC. Twin pairs withconfi rmed diagnosis were assembled in a combined Scandinavian cohort. 158 twins with ulcerative colitis (UC) (18 be-Scand J Gastroenterol Downloaded from informahealthcare.com by University of Orebro on 08/21/14For personal use only.36longing to 9 concordant monozygotic pairs) and 141 twins with Crohn’s disease (CD) (34 belonging to 17 concordantmonozygotic pairs) were enrolled. Using the binominal distribution, we tested the hypothesis that clinical characteristicswere independent within individuals in disease concordant monozygotic pairs.
Results: In CD, difference in age at diagnosis was < 5 years within 14 of 17 pairs (p<0.00001). Location was identicalin 11/17 monozygotic concordant pairs at diagnosis (p=0.008) and in 11/16 pairs after 10 years (p=0.02). Behavior atdiagnosis was identical in 13/17 pairs (p=0.03) and in 11/16 pairs after 10 years (p=0.01). Monozygotic UC twins wereconcordant (within 5 years) for age at diagnosis (6/9 pairs; p<0.001) and symptomatic onset (4/9 pairs; p=0.02) but notfor extent of disease at diagnosis or after 10 years. Concordance for “colectomy or not”, was observed in 7 of 9 pairs(p=0.15).
Conclusion: The high phenotypic concordance, both at diagnosis and longitudinally, in monozygotic twins with CDsupports a genetic infl uence not only on disease occurrence but also on disease course. This contrasts to UC, wherethe genetic impact appears less.