1. From the Wellcome Sanger Institute, Hinxton (T.H.H.C., T.J.M., S.L., S.B.), Cambridge University Hospitals NHS Foundation Trust (S.J.F., T.J.M., S.B.) and the Departments of Surgery (T.J.M.) and Paediatrics (S.B.), University of Cambridge, Cambridge, and UCL Great Ormond Street Institute of Child Health (N.J., N.S., J.A.), Great Ormond Street Hospital for Children NHS Foundation Trust (N.J., N.S., J.A.), and the Royal Marsden NHS Foundation Trust (M.H.), London — all in the United Kingdom.