The major psychoses

Abstract

Schizophrenia and the manic depressive or affective psychoses are the major mental disorders of adult life in which genetic factors have been established as playing an important part. The life time expectancy for someone from the general population developing schizophrenia is probably best taken to be around 1%. Problems of diagnosis and heterogeneity are even greater in the case of the affective psychoses. Bipolar manic depressive psychosis is probably less frequent than schizophrenia and simple unipolar endogenous depression more frequent, but it is difficult to give a firm figure because of the difficulty in drawing a firm line between the endogenous and reactive. The total expectancy for any of these schizophrenic or affective psychoses may be somewhere approaching 5%. To this one should add something like 2.5% for senile dementia, given survival to the age of 80. Among the major psychoses the morbid risk for the children in schizophrenia (about 10%) is lower than that in manic depressive psychosis, but schizophrenia must be regarded as the more detrimental condition. Most current theories do not rely on new mutations for maintaining disorders like schizophrenia in the population. The genes involved are probably polymorphic, i.e. have a frequency of more than 1% in the gene pool. Instead, selective advantage of heterozygotes is invoked or, alternatively, a compensating minor reduction in fitness of the nonschizophrenic alleles in other polygenic settings. If aetiology is multifactorial the psychoses may be relatively insensitive to changes in mutation rate.