Background: Lymphoid follicles (LFs) have been suggested to play a role at the early stage of Crohn’s disease (CD) lesions. In the small bowel, LFs are grouped, forming Peyer’s patches, which de- velop early in fetal life, grow in size and number until puberty, and undergo involution. In contrast, colonic LFs are isolated and undergo little change during life. As a result, if LFs play a role in the oc- currence of CD lesions, the distribution of ileal and colonic lesions is expected to be altered in small children.
Methods: Medical records of 2 independent French (n = 136) and Swedish (n = 55) cohorts of consecutive pediatric CD were reviewed. Disease sites and age of onset were recorded, and the age-dependent probability to develop ileal lesions was computed. The CARD15/NOD2 genotype was also analyzed when available (n = 99).
Results: The curves of disease occurrence were significantly differ- ent in case of CD with or without ileal lesions (P , 0.0001). At the age of 8 years, the probability (95% confidence interval) of small bowel involvement was 0.19 (0.07–0.39). It increased until 16 years of age to 0.61 (0.54–0.68). It was slightly higher in patients carrying 1 or more CARD15/NOD2 mutations [0.75 (0.55–0.89)] than in wild- type patients [0.46 (0.34–0.58)]. CARD15 mutations also influenced the age of onset of ileal disease (P , 0.02).
