1. Department of Epidemiology, Faculty of Health, Medicine and Life Sciences, Care and Public Health Research Institute, Maastricht University, Maastricht, the Netherlands
2. Rett Expertise Centre, Maastricht University Medical Centre and School for Mental Health and Neuroscience, Maastricht University, Maastricht, the Netherlands
3. Dutch Rett Syndrome Association (NRSV), Utrecht, the Netherlands
4. Department of Clinical Epidemiology and Medical Technology Assessment, Maastricht University Medical Centre, Maastricht, the Netherlands
5. Department of Orthopedic Surgery, Maastricht University Medical Center, Maastricht, the Netherlands
6. Department of Orthopedic Surgery, Universitair Medisch Centrum Utrecht, Utrecht, the Netherlands