Relevance of pre-morbid cognitive impairment of schizophrenia

Abstract

This thesis begins with an exploration of the historical associations between learning disability and schizophrenia, which leads to the modern supposition that schizophrenia is commoner in people with learning disability than the normal population. A critical evaluation of both community and hospital epidemiological studies indicates that the point prevalence of schizophrenia in people with mild learning disability is around 3% i.e. around three times that expected in the normal population. Five possible mechanisms to account for this increase are postulated and discussed: a chance co-occurrence, a common aetiology, an epiphenomenon, a severe schizophrenia and a 'de novo' disease.