[1] Barberry Natl Ctr Mental Hlth, Dept Neuropsychiat, Birmingham B15 2FG, W Midlands, England
[2] UCL, Inst Neurol, Sobell Dept Motor Neurosci & Movement Disorders, London, England
[3] Univ Catania, Dept Pediat, Sect Child Neurol & Psychiat, Catania, Italy
[4] Univ Catania, Dept Biomed Sci, Catania, Italy
[5] Univ London St Georges Hosp, Sch Med, London SW17 0RE, England
[6] UCL, Dept Mental Hlth Sci, London, England