Systematic Review of the Clinical Presentation of Schizophrenia in Intellectual Disability

Schizophrenia and intellectual disability (ID) co-occur three times more than would be expected by chance. This has led to speculation that a particular form of schizophrenia may give rise to both the symptoms of schizophrenia and the intellectual impairment. If this was the case, one may expect the presentation of schizophrenia in an ID population to differ from that in a population with average/high IQ. A systematic review and meta-analysis was undertaken of studies comparing the clinical presentation of schizophrenia in people with mild/borderline ID to that in people with average/high IQ. Five studies were eligible for inclusion. Four reported more negative symptoms in the ID population, while two reported more positive symptoms. Meta-analysis demonstrated that the ID population experienced more negative symptoms. The available evidence supports the proposal that the clinical presentation of schizophrenia in an ID population differs from that in a population with normal IQ.