[1] Johns Hopkins Univ, Sch Med, Dept Med, Harvey M & Lyn P Meyerhoff Inflammatory Bowel Dis, Baltimore, MD 21231 USA
[2] Johns Hopkins Univ, Bloomberg Sch Publ Hlth, Dept Epidemiol, Baltimore, MD 21231 USA
[3] Univ Oxford, Wellcome Trust Ctr, Human Genet & Gastroenterol Dept, Oxford, England