The Search for the Psychosis Gene

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Abstract
The major psychoses remain an enigma. Affective and schizophrenic psychoses are apparently present (probably at about the same lifetime prevalence of approximately 2%) in all human societies. Yet their aetiology is obscure. While a genetic contribution is acknowledged by most authorities, few accept that genes are a sufficient explanation of causation because: onset is in adult life; psychosis – particularly schizophrenia – is associated with a substantial fertility disadvantage; and most cases lack a family history of illness. But genetic determination has to be considered because onset is determined by chronological age rather than environmental insult (Crow & Done, 1986), adoption away from a family with schizophrenia does not reduce risk of illness, and no plausible environmental precipitant of psychosis has been identified. The fact that psychosis occurs across widely differing climatic, industrial, and social environments without obvious variations in incidence suggests that the disease is relatively independent of the external milieu. The suggestion that birth injury is relevant has been tested in a prospective study (the National Child Development Study) and found wanting (Done et al, 1991).