1. Department of Speech and Language Therapy, Aberdeen Royal Infirmary, Aberdeen, Scotland, UK
2. Department of Neurology, Leiden University Medical Centre, Leiden, The Netherlands
3. Department of Speech & Language Therapy, Huntington Centre, Topaz, Overduin, Katwijk, The Netherlands
4. National Hospital for Neurology & Neurosurgery, UCLH NHS Foundation Trust, London, UK
5. Department of Speech & Language Therapy, Royal Hospital for Neuro-disability, Putney, London, UK
6. Department of Clinical Genetics, NHS Grampian, Aberdeen, Scotland, UK
7. University of Aberdeen, Aberdeen, AB25 2ZA Scotland, UK
8. Department of Clinical Genetics, NHS Grampian, Aberdeen, Scotland, UK.