1. From the Dubowitz Neuromuscular Centre (F.M., M.C., A.Y.M.), NIHR Great Ormond Street Hospital Biomedical Research Centre, Great Ormond Street Institute of Child Health, University College London, and Great Ormond Street Hospital Trust, United Kingdom; Analysis Group, Inc. (J.S., G.S., H.L., M.J., I.D.), Boston; The Collaborative Trajectory Analysis Project (J.S., S.J.W.), Cambridge, MA; Department of Physical Medicine and Rehabilitation, and Pediatrics (C.M.), University of California, Davis,...