1. Dept. Developmental Biology, Stanford University Medical Center, Stanford CA, USA
2. Dept. of Medicine, Stanford Prevention Research Center and Dept. of Health Research and Policy, Division of Epidemiology, Stanford University School of Medicine, and Dept. of Statistics, Stanford University School of Humanities and Sciences, Stanford CA, USA
3. Dept. Physical Medicine and Rehabilitation, Harvard Medical School, Boston MA, USA
4. Kaiser Permanente Northern California, Division of Research, Oakland, California, USA
5. Dept. Orthopaedic Surgery, Stanford University Medical Center, Stanford CA, USA