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Evidence of a cohort effect for age at onset of schizophrenia.

OBJECTIVE
The authors address whether a possible age-at-onset cohort effect may have introduced a bias into anticipation studies of schizophrenia.


METHOD
A retrospective review of the medical records of all admissions for psychotic disorders (N=877) was conducted. All subjects with a confirmed DSM-IV diagnosis of schizophrenia and age-at-onset data were included (N=419). For analyses, subjects were placed into one of three successive birth cohorts: 1905-1944 (N=96), 1945-1964 (N=200), and 1965-1984 (N=123).


RESULTS
The mean age at first appearance of psychotic symptoms and, similarly, the mean age at first hospitalization significantly decreased over time in successive birth cohorts (25.3, 23.3, and 20.4 years, respectively, for age at first appearance of psychotic symptoms).


CONCLUSIONS
This potential birth cohort effect for age at onset of schizophrenia needs to be incorporated into genetic models.