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  • Title: Premorbid intra-individual variability in intellectual performance and risk for schizophrenia: a population-based study.
    Author: Reichenberg A, Weiser M, Rapp MA, Rabinowitz J, Caspi A, Schmeidler J, Knobler HY, Lubin G, Nahon D, Harvey PD, Davidson M.
    Journal: Schizophr Res; 2006 Jul; 85(1-3):49-57. PubMed ID: 16626941.
    Abstract:
    BACKGROUND: Some, but not most, schizophrenia patients have below-average intelligence years before they manifest psychosis. However, it is not clear if those whose intelligence falls within-normal-range nevertheless have cognitive abnormalities. We examined the association between intra-individual variability in intellectual performance and risk for schizophrenia in individuals with normal IQ. METHODS: 555,326 adolescents, mandatory assessed by the Israeli Draft Board were followed up over 8 to 17 years for psychiatric hospitalization by means of the Israeli National Psychiatric Hospitalization Case Registry. Data were available on 4 intelligence sub-tests, and on behavioral and psychosocial variables. Variability was computed from the variance of the four intelligence tests' standardized scores. RESULTS: There was a significant monotonic association between increased intra-individual variability in intellectual performance and risk of schizophrenia in individuals with within-normal-range IQ. Individuals with the highest variability were 3.8 times more likely to have schizophrenia [95%CI: 2.32-6.08; p < 0.0001] compared with individuals with the lowest variability. This association held after controlling for the effects of potential confounders. CONCLUSIONS: Despite within-normal-range premorbid IQ, apparently healthy adolescents who will later on manifest schizophrenia, nevertheless have cognitive abnormalities such as increased variability across intellectual tasks, possibly related to frontal lobe abnormalities.
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