Genetic analyses showed that mutations affecting the interleukin-10 receptor are associated with early-onset colitis. Further molecular analyses showed that the mutations abrogated interleukin-10 signaling. Treatment of one of the affected children by means of allogeneic hematopoietic stem-cell transplantation was successful. Genetic analyses showed that mutations affecting the interleukin-10 receptor are associated with early-onset colitis. Treatment of an affected child by means of allogeneic hematopoietic stem-cell transplantation was successful. Inflammatory bowel disease is a heterogeneous group of disorders, classified as Crohn's disease, ulcerative colitis, and indeterminate colitis. 1 , 2 In most patients, these disorders are manifested in adolescence or adulthood; however, they may present in infancy and may be inherited as an autosomal recessive trait. 3 – 6 The genetic causes of inflammatory bowel disease are only partly understood. Studies in transgenic murine models 7 and genomewide genetic-linkage and association studies have provided insights into the genetic complexity underlying these inflammatory conditions. 8 Investigators using these approaches have implicated several genes in the pathogenesis of inflammatory bowel disease; the identity of these genes suggests . . .