Objectives: A Danish cohort of twins with inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC), has previously been collected. The aim of the present study was to reassess this cohort in order to compare clinical characteristics in concordant versus discordant twin pairs, test twin zygosity genetically, follow-up on disease concordance, and examine NOD2/CARD15 genetic status.
Methods: The Danish cohort is one of two population-based cohorts worldwide and consists of 103 twin pairs. After median 13 yr of follow-up, all twins were contacted and hospital files were scrutinized to reassess disease concordance and obtain phenotype data. DNA was obtained from 123 twins for analysis of zygosity and prevalence of the three common NOD2/CARD15 mutations.
Results: Zygosity tested genetically was consistent with the former assessment based on questionnaires. The proband concordance for CD remained fairly stable: 63.6% among monozygotic (MZ) twins and 3.6% among dizygotic (DZ) twins. Clinical characteristics were similar in twins from concordant versus discordant pairs. Forty-four percent of patients with CD were positive for >or=1 mutant allele of NOD2/CARD15 compared to 2% of UC patients (p < 0.001) and 19% of healthy twins (p= 0.02). The allele mutation frequency was 43% among the healthy twins to patients with CD versus 9% among twins to UC patients (p= 0.01).
Conclusions: Previous questionnaire assessment of twin zygosity was confirmed by genetic test. Concordance for CD remained quite stable and was significantly higher among MZ than DZ twins. A high NOD2/CARD15 mutation frequency was observed both among CD twins and their healthy siblings.