Evidence from longitudinal studies indicates that lower IQ score in childhood and early adolescence increases risk of schizophrenia and schizophrenia spectrum disorders (SSD). This study investigated the association between premorbid IQ and risk of SSD in a population-based cohort of 17-year-old conscripts. Fifty four thousand males assessed by the Israeli Draft Board during two consecutive years were followed by means of the Israeli National Psychiatric Hospitalization Case Registry for up to II years. Tests of verbal and non-verbal reasoning, mathematical knowledge and instructions comprehension and several psychosocial variables were recorded by the Draft Board. Risk for SSD increased with decreasing IQ score. Only poorer non-verbal reasoning conferred a significant increased risk for SSD after taking into account general intellectual ability. IQ was not associated with age of onset. These results confirm the importance of low intellectual functioning as a risk factor for SSD. This is unlikely to be due to prodrome.
|Number of pages||15|
|Journal||Journal of Clinical and Experimental Neuropsychology|
|State||Published - Feb 2006|
Bibliographical noteFunding Information:
Intellectual deviations from population norms are very common among patients with schizophrenia. Between 75% and 85% of all schizophrenia patients exhibit abnormal intellectual functioning, including below normal IQ, as well as abnormal declarative memory, working memory, attention and executive functioning (Calev, Venables, & Monk, 1983; Cannon et al., 1994; Goldberg et al., 1990; Kremen, Seidman, Faraone, Toomey, & Tsuang, 2000; Saykin et al., 1991; Saykin et al., 1994). Between 5%–25% of schizophrenia patients perform outside normal limits (DeLisi et al., 1995; Goldberg & Gold, 1995; Goldberg et al., 1990; Hoff et al., 1999; Kremen et al., 2000). Prospective longitudinal studies of patients with first-episode schizophrenia have demonstrated that the cognitive dysfunction remains stable in most domains, including attention, memory, This study was supported in part by a grant from the German Federal Ministry of Education and Research (BMBF) within the framework of German Israeli Project Cooperation (DIP) to Jonathan Rabinowitz, and by a grant from the Stanley Foundation to Michael Davidson and Mark Weiser.