• schizophrenia;
  • longitudinal studies;
  • risk factors;
  • intelligence;
  • Wechsler scales

Objective: Performance IQ (PIQ) is often lower than verbal IQ (VIQ) in schizophrenic patients. Whether PIQ<VIQ precedes psychotic symptoms in schizophrenia remains uncertain.

Method: We investigated premorbid IQ scores in 63 subjects assessed at a child and adolescent psychiatric unit (mean age 13.1 years, SD 3.2), who at follow-up in adulthood (mean age 30.9 years, SD 3.9) received a lifetime RDC diagnosis of schizophrenia-related psychosis, affective disorder, or no psychiatric disorder.

Results: Premorbid PIQ<VIQ significantly differentiated the groups with schizophrenia-related psychosis and no psychiatric disorder. Subjects with schizophrenia-related psychosis had a significantly lower mean value for premorbid PIQ, but not VIQ, compared to subjects who developed affective disorder or subjects without psychiatric disorder.

Conclusion: Our results emphasize premorbid intellectual deficits in schizophrenia. Those deficits might largely be in consequence of an impairment on the PIQ scale.