a1 Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King's College London, UK
a2 Research Unit for Schizophrenia Epidemiology, School of Psychiatry, University of New South Wales, Sydney, Australia
a3 Schizophrenia Research Institute, Sydney, Australia
a4 Département de Psychiatrie, Université de Montréal, Canada
a5 Department of Psychiatry, Heidelberg University, Germany
Background Previous reviews have reported cognitive and motor deficits in childhood and adolescence among individuals who later develop schizophrenia. However, these reviews focused exclusively on studies of individuals with affected relatives or on population/birth cohorts, incorporated studies with estimated measures of pre-morbid intelligence, or included investigations that examined symptomatic at-risk participants or participants 18 years or older. Thus, it remains unclear whether cognitive and motor deficits constitute robust antecedents of schizophrenia. Meta-analyses were conducted on published studies that examined cognitive or motor function in youth aged 16 years or younger who later developed schizophrenia or a schizophrenia spectrum disorder (SSD) and those who did not.
Method Twenty-three studies fulfilled the following inclusion criteria: (1) written in English; (2) prospective investigations of birth or genetic high-risk cohorts, or follow-back investigations of population samples; (3) objective measures of cognitive or motor performance at age 16 or younger; (4) results provided for individuals who did and who did not develop schizophrenia/SSD later in life; and (5) sufficient data to calculate effect sizes. Four domains of function were examined: IQ; Motor Function; General Academic Achievement; and Mathematics Achievement.
Results Meta-analyses showed that, by age 16, individuals who subsequently developed schizophrenia/SSD displayed significant deficits in IQ (d=0.51) and motor function (d=0.56), but not in general academic achievement (d=0.25) or mathematics achievement (d=0.21). Subsidiary analysis indicated that the IQ deficit was present by age 13.
Conclusions These results demonstrate that deficits in IQ and motor performance precede the prodrome and the onset of illness.
(Received November 23 2010)
(Revised July 29 2011)
(Accepted August 04 2011)
(Online publication September 06 2011)
c1 Address for correspondence: H. Dickson, Department of Forensic and Neurodevelopmental Sciences (Box P023), Institute of Psychiatry, King's College London, De Crespigny Park, London SE5 8AF, UK. (Email: email@example.com)