We report the global pattern of ileal gene expression in a cohort of 310 treatment-naÃ¯ve pediatric Crohn Disease patients and controls. We focus on genes with consistent altered expression in the ileum of younger (Paris age A1a) vs older (Paris age A1b) patients. 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 normal radiographic, endoscopic, and histologic findings. Biopsies were stored at -80 degrees.