TUESDAY, Sept. 2 (HealthDay News) -- The older the father, the greater his child's risk for bipolar disorder.

That's the conclusion of a new study by Swedish researchers who compared 13,428 people with bipolar disorder to more than 67,000 people without the condition.

"After controlling for parity (number of children), maternal age, socioeconomic status and family history of psychotic disorders, the offspring of men 55 years and older were 1.37 times more likely to be diagnosed as having bipolar disorder than the offspring of men aged 20 to 24 years," wrote Emma M. Frans, of the Karolinska Institute in Stockholm, and colleagues.

Children of older mothers also had an increased risk, but the risk was less pronounced than that associated with older fathers. In cases of early onset bipolar disorder (diagnosed before age 20), the effect of the father's age was much stronger, while the mother's age had no effect, the study found.

"Personality of older fathers has been suggested to explain the association between mental disorders and advancing paternal age. However, the mental disorders associated with increasing paternal age are under considerable genetic influence," the study authors wrote.

This suggests a genetic link between the advancing age of the father and bipolar and other disorders among children, the researchers said.

"As men age, successive germ cell replications occur, and de novo (new, not passed from parent to offspring) mutations accumulate monotonously as a result of DNA copy errors," the researchers noted.

"Women are born with their full supply of eggs that have gone through only 23 replications, a number that does not change as they age. Therefore, DNA copy errors should not increase in number with maternal age. Consistent with this notion, we found smaller effects of increased maternal age on the risk of bipolar disorder in the offspring."

The study was published the September issue of the journal Archives of General Psychiatry.

Bipolar disorder is a common, severe mood disorder involving episodes of mania and depression. Other than a family history of psychotic disorders, few risk factors for the condition have been identified, according to background information in the article.

More information

The U.S. National Institute of Mental Health has more about bipolar disorder.