We report the global pattern of ileal gene expression in a cohort of 359 treatment-naÃ¯ve pediatric Crohn Disease, Ulcerative Colitis patients and controls. We focus on genes with consistent altered expression in inflamed and unaffected ileum of CD [ileal-involved CD (iCD) and non-invloved ileal CD (cCD)], but not in the ileum of ulcerative colitis or control. Overall design: Ileal biopsies were obtained during diagnostic colonoscopies of children and adolescents aged less than 17 years, who presented with IBD-like symptoms. All patients underwent baseline colonoscopy and histological characterization; non-IBD controls were those with suspected IBD, but with no microscopic or macroscopic inflammation and normal radiographic, endoscopic, and histologic findings. Biopsies were stored at -80 degrees.