Associations between premorbid intellectual performance, early-life exposures and early-onset schizophrenia. Cohort study

Abstract

Background: Impaired intellectual performance is associated with an increased risk of schizophrenia.

Aims: To investigate whether this association is due to the influence of prenatal and early childhood exposures on both intellectual development and the risk of schizophrenia.

Method: Cohort of 197 613 Swedish male conscripts with linked birth, census and hospital admission data together with five measures of verbal and non-verbal intellectual performance recorded at conscription.

Results: 109 643 subjects had complete data; over a mean 5-year follow-up, 60 developed schizophrenia and 92 developed other non-affective psychoses. Poor scores for each of the five tests were associated with 3- to 14-fold increased risk of psychosis, particularly schizophrenia. Controlling for birth-related exposures, including birth weight, and parental education did not attenuate these associations.

Conclusions: Poor intellectual performance at 18 years of age is associated with early-onset psychotic disorder. Associations do not appear to be confounded by prenatal adversity or childhood circumstances, as indexed by parental education.