Halfvarson J. Inflamm Bowel Dis 2011;17:6–12.
A number of twin studies have previously been conducted to estimate concordance rates and thus the genetic contribution in IBD. However, many of these studies have had methodological limitations, including the lack of standardization according to age. This author aimed to establish concordance rates for Crohn’s disease and ulcerative colitis, and also to evaluate phenotypes in concordant and discordant twin pairs.
IBD is a multifactorial disorder of unknown etiology. In 1988, this Swedish group published the first study of an unselected cohort of twins with IBD, born 1886–1958, and showed a higher concordance rate for Crohn’s disease than for ulcerative colitis (UC) [1]. In the present study, the Swedish twin registry was re-run, this time utilizing the Swedish hospital discharge register. The aims were, firstly, to establish reliable concordance rates, and secondly, to compare phenotypic characteristics in concordant and discordant monozygotic pairs. The initial twin cohort consisted of 80 twin pairs, where at least one twin in each pair suffered from IBD. By sending a questionnaire (including questions on diagnosis of IBD) to all twins born between 1909 and 1980, 149 new twin pairs with IBD were identified. The analyses were then restricted to the new twin pairs born during the same period as the original cohort and the results were as follows: none of 39 pairs were concordant for Crohn’s disease; three of 25 monozygotic and three of 32 dizygotic pairs were concordant for UC. Furthermore, by making a comparison between concordant and discordant monozygotic twins with Crohn’s disease in the total population born between 1886 and 1980, colonic disease seemed to be less common in the concordant pairs. In addition, there was an increase of this phenotypic characteristic in twins diagnosed during 1981–2000 compared with 1961–1980 (p=0.004).