Elaboration on Premorbid Intellectual Performance in Schizophrenia: Premorbid Intellectual Decline and Risk for Schizophrenia

Arch Gen Psychiatry. 2005 Dec;62(12):1297-304. doi: 10.1001/archpsyc.62.12.1297.

Abstract

Context: 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.

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

Setting: Mandatory assessment by the draft board of Israeli conscripts.

Participants: 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.

Main outcome measures: 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Age Factors
  • Child
  • Cohort Studies
  • Developmental Disabilities / diagnosis
  • Developmental Disabilities / epidemiology*
  • Female
  • Hospitalization / statistics & numerical data
  • Humans
  • Intelligence Tests / statistics & numerical data*
  • International Classification of Diseases / statistics & numerical data
  • Israel / epidemiology
  • Male
  • Military Personnel / statistics & numerical data
  • Registries
  • Regression Analysis
  • Risk Factors
  • Schizophrenia / diagnosis
  • Schizophrenia / epidemiology*