Premorbid intra-individual variability in intellectual performance and risk for schizophrenia: a population-based study.
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.
Reichenberg
Abraham
A
Department of Psychiatry, Mount Sinai School of Medicine, New York, NY 10029, USA. avi.reichenberg@mssm.edu
Weiser
Mark
M
Rapp
Michael A
MA
Rabinowitz
Jonathan
J
Caspi
Asaf
A
Schmeidler
James
J
Knobler
Haim Y
HY
Lubin
Gad
G
Nahon
Daniela
D
Harvey
Philip D
PD
Davidson
Michael
M
D000293:Adolescent; D002648:Child; D003072:Cognition Disorders / Q000175:diagnosis / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D005625:Frontal Lobe / Q000002:abnormalities / Q000503:physiopathology; D006760:Hospitalization; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D011159:Population Surveillance / Q000379:methods*; D012042:Registries; D012307:Risk Factors; D012559:Schizophrenia / Q000453:epidemiology* / Q000503:physiopathology / Q000534:rehabilitation; D012720:Severity of Illness Index; D013997:Time Factors