1. From the Divisions of Gastroenterology and Nutrition (B.M.K., D.A.P.) and Human Genetics and Molecular Biology (N.B.S., I.D.K.), The Children’s Hospital of Philadelphia and The University of Pennsylvania School of Medicine, Philadelphia, Pa; the Division of Gastroenterology and Nutrition, Northwestern University Medical School, Children’s Memorial Hospital, Chicago, Ill (K.M.E.); Children’s Hospital and University of Manitoba, Winnipeg, Canada (A.E.C.); and Lutheran General Children’s Hospital, Park...