Introduction IBD twin studies have shown similar disease phenotype within concordant pairs. Longitudinal follow up suggests pairs with CD remain concordant for location whereas twins with UC diverge.¹This study is a retrospective longitudinal analysis of UK twin pairs with IBD.

Method The UK IBD Twin and Multiplex Registry was searched for twin pairs who took part in a previous twin study. Data from 1994 and 2014 was reviewed. The following were analysed: zygosity, concordance, Montreal classification, admissions, surgical history.

Results Demographics: N=94 twin pairs. UC:CD 48:46. Mean age 59.

Pair Concordance:

3 previously discordant pairs became concordant. The mean time between diagnosis was 9.1 years.

Montreal Classification:

Concordant Pairs: There were no mixed CD:UC pairs. Of the 17 concordant pairs, 10 had complete information from both twins in both datasets.

IBD: A was identical in 6/12 (50%) concordant pairs.

CD: L was identical in 3/6 (50%) pairs in both 1994 and 2014. B was only available from 2014, and was identical in 3/6 (50%) pairs. P was identical in 2/5 (40%) twins in 1994 and 3/7 (43%) twins in 2014.

UC: A was identical in 3/4 pairs (74%). L was identical in 4/4 (100%) pairs in 1994 and 2014.

All IBD sufferers:

UC: Disease classified as proctitis decreased from 1994 to 2014 (30.4% vs 17.9%), with a corresponding increase in pancolitis (41.1% vs 50%).

CD: Cases classified as L3 increased from 6/52 (11.5%) to 22/53 (41.5%). Presence of perianal disease also increased (9.6% vs 23.1%).

Extraluminal manifestations increased from 4/109 (3.7%) to 13/112 (11.6%).

Surgery:

Concordant pairs:Concordant twin pairs were concordant for history of previous surgery in 9/12 (75%) pairs in 1994 and 7/14 (50%) pairs in 2014.

All IBD: In 1994 32/109 (29.4%) IBD sufferers had undergone surgery, increasing to 52/112 (49.1%) in 2014.

Admission:

Concordant pairs:Concordant twins were concordant for history of admission in 10/14 (71.4%) pairs in 1994 and 10/15 (66.7%) pairs in 2014.

All IBD: 46/109 (42.2%) IBD sufferers had at least one admission in 1994; this increased to 76/112 (67.9%) in 2014.

Conclusion Pair concordance of this cohort supports that heritability of CD is greater than UC. Within concordant pairs with CD, disease location is less correlated than in other cohorts. Conversely, concordant pairs within UC were more similar and converged over time. Sample size limited analysis. Disease progressed over time.

Disclosure of interest None Declared.

Reference

1. Halfvarson, et al. Longitudinal concordance for clinical characteristics in a Swedish-Danish twin population. IBD 2007