[1] Kings Coll London, Inst Psychiat, London SE5 8AF, England
[2] Maudsley Hosp & Inst Psychiat, Natl & Specialist OCD Clin Young People, London SE5 8AZ, England
[3] Autonomous Univ Barcelona, Dept Psychiat & Legal Med, E-08193 Barcelona, Spain
[4] UCL, Inst Child Hlth, London WC1E 6BT, England