Older paternal age has previously been associated with a higher risk of autism but this is the first time that it has been linked to bipolar disorder.
The researchers identified 13,428 patients, born between 1932-1991, who had been diagnosed with bipolar disorder and had information available on the age of both their parents.
For each bipolar sufferer, they randomly selected five controls who were of the same sex and born the same year but did not have the disorder.
When comparing the two groups, the older an individual's father, the more likely he or she was to have bipolar disorder.After adjusting for other risk factors for the disorder such as socioeconomic status and family history of psychotic disorders, the researchers found that there was a significant increase in the risk of bipolar disorder in children of fathers who were older than 29 years.
The highest risk of bipolar disorder was found in children of men aged 55 and over who were 1.37 times more likely to have the disorder than offspring of men aged 20 to 24. Children born to older mothers had a small, but not statistically significant, increased risk of developing the disorder.
Lead researcher Dr Emma Frans, from the Karolinska Institute in Stockholm, said: 'The link between advancing paternal age and bipolar disorder could be a result of genetic alterations. As men age, successive germ cell replications occur and the mutations risk increases.'
But this is not the case for women who are born with their full supply of eggs, that have gone through only 23 replications, a number that does not change as they age, said Dr Frans.
Future studies are now being planned to identify the genetic alterations in relation to paternal age, she added.
- Arch Gen Psychiatry 2008; 65: 1,034-40.
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