These findings add weight to the theory that accumulating mutations in the sperm of older fathers contributes to the overall risk of schizophrenia.

The study involved over 700,000 people born in Sweden between 1973 and 1980. The analysis was based on records of people admitted to hospital between 1989-2001 with a diagnosis of schizophrenia or other non-affective psychosis.

There was a strong association between increased paternal age at conception and their offspring's risk of schizophrenia, which remained even after taking account of a range of other factors that could have affected the results.

Overall, 15.5% of cases of schizophrenia in this group may have been due to the patient having a father who was aged over 30 years at birth, say the authors.

The association seemed to be relatively specific to schizophrenia compared with non-affective psychosis and was stronger in those with no family history of the disorder. This supports the theory that accumulating mutations in the germ lines of older fathers might contribute to an increased risk of schizophrenia, they add.

In England and Wales the average paternal age has increased from 29.2 years in 1980 to 32.1 in 2002. Based on their data, the authors estimate that this increase could have led to an additional 710 cases of schizophrenia in 2002 over and above the 5,923 cases due to the background incidence rate.

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Contact: Emma Dickinson
edickinson@bmj.com
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BMJ-British Medical Journal
21-Oct-2004