[1] Univ Newcastle Upon Tyne, Sir James Spence Inst, Royal Victoria Infirm, Newcastle Upon Tyne NE1 4LP, Tyne & Wear, England
[2] Univ London St Georges Hosp, Paediat Neurol Dept, London SW17 0QT, England
[3] Leiden Univ, Ctr Med, Ctr Human & Clin Genet, NL-2300 RC Leiden, Netherlands
[4] Univ Amsterdam, Acad Med Ctr, Dept Neurol H2 237, NL-1100 DD Amsterdam, Netherlands