1. Department of Epidemiology & Biostatistics, Erasmus MC, Rotterdam, The Netherlands
2. Dichterbij, Centre for the Intellectually Disabled, Gennep, The Netherlands
3. Department of General Practice, Intellectual Disability Medicine, Erasmus MC, Rotterdam, The Netherlands
4. s'-Heeren Loo-Midden Nederland, Centre for the Intellectually Disabled, Ermelo, The Netherlands
5. Department of Neurology, Academic Medical Centre, Amsterdam, The Netherlands