Elaboration on premorbid intellectual performance in schizophrenia: premorbid intellectual decline and risk for schizophrenia.
BACKGROUND
Consistent evidence indicates that some, but not most, patients with schizophrenia have below-average intelligence years before they manifest psychosis. However, it is not clear whether this below-average premorbid intelligence is stable or progressive.


OBJECTIVE
To examine whether increased risk for schizophrenia is associated with declining intellectual performance from childhood through adolescence.


METHODS
Historical cohort study of an entire population using record linkage for psychiatric hospitalization during an 8- to 17-year follow-up period.


METHODS
Mandatory assessment by the draft board of Israeli conscripts.


METHODS
Population-based cohort of 555 326 adolescents born in Israel. Data were available on 4 intelligence subtests as well as on reading and spelling abilities and on behavioral and psychosocial variables. A regression-based approach was used to assess the discrepancy between actual IQ at age 17 years and estimated IQ during childhood based on reading and spelling abilities.


METHODS
Hospitalization for schizophrenia (as per the International Statistical Classification of Diseases, 10th Revision criteria).


RESULTS
Lower-than-expected IQ at age 17 years was associated with increased risk for later hospitalization for schizophrenia. Results were held after controlling for potential confounders. For 75% of patients with schizophrenia with low actual IQ (<85) at age 17 years and for 23% of patients with actual IQ within the normal range (> or =85), actual IQ was 10 or more points lower than expected. Lower-than-expected IQ was not associated with bipolar disorder or with depression or anxiety disorder.


CONCLUSIONS
Indirect evidence suggests that intellectual deterioration from childhood through adolescence is associated with increased risk for schizophrenia. Despite within-normal-range premorbid IQ scores, apparently healthy adolescents who will later manifest schizophrenia nevertheless have intellectual decline.
Reichenberg
Abraham
A
Department of Psychiatry, Mount Sinai School of Medicine, One Gustave L. Levy Place, 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; D000367:Age Factors; D002648:Child; D015331:Cohort Studies; D002658:Developmental Disabilities / Q000175:diagnosis / Q000453:epidemiology*; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007361:Intelligence Tests / Q000706:statistics & numerical data*; D038801:International Classification of Diseases / Q000706:statistics & numerical data; D007557:Israel / Q000453:epidemiology; D008297:Male; D008889:Military Personnel / Q000706:statistics & numerical data; D012042:Registries; D012044:Regression Analysis; D012307:Risk Factors; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology*