ObjectivesCrohn disease is a chronic inflammatory bowel disorder that is caused by environmental and genetic factors. Mutations in theCARD15gene have been recently identified to be associated with the disease. Until now no genetic study has focused directly on a pediatric population.MethodsThe authors sequenced all 12 exons of theCARD15gene in 55 pediatric patients with Crohn disease from Saxony. Their average age at onset was 11.2 years (1–17.5 years). The authors also evaluated the genotype-phenotype relationship in the patients.ResultsFourteen different polymorphic and/or disease-related nucleotide alterations have been identified in the patients. Sixty-five percent of their genomic DNA samples harbored at least one of six mutations within theCARD15gene, which previously has been identified as being associated with Crohn disease. The authors found that the cytosine insertion mutation 3020insC was significantly more common in their pediatric population than in patients with Crohn disease (26% versus 11% of the alleles) whose results were reported in the literature. The genotype–phenotype analysis showed that the authors' patients with at least one of the sixCARD15disease-associated mutations had a high risk of inflammation located in the terminal ileum and ascending colon. In 10 of 19 patients with two mutations, intestinal resection surgery was necessary because of stricturing.ConclusionsIn the authors' pediatric patients, the genetic influence on Crohn disease was more pronounced than that reported in any other study, and it strongly affected the clinical phenotype.