2 September 2008
Older sperm more likely to produce bipolar kids
by George Atkinson
Age-related sperm abnormalities appear to be behind a statistically significant increase in the number of bipolar children born to older dads, suggests a report in the Archives of General Psychiatry. Older paternal age has previously been associated with a higher risk of other neurological disorders - such as schizophrenia and autism - but the bipolar association has not been suggested before.
To undertake the study, lead researcher Emma M. Frans, of the Karolinska Institute in Sweden, identified 13,428 patients in Swedish birth registries with a diagnosis of bipolar disorder. For each one, Frans randomly selected from the registries five controls who were the same sex and born the same year but did not have bipolar disorder. When comparing the two groups, it was found that the older an individual's father, the more likely he or she was to have bipolar disorder.
"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," Frans explained. Interestingly, the offspring of older mothers also had an increased risk, but it was less pronounced than the paternal effect. For early-onset bipolar disorder (diagnosed before age 20), the effect of the father's age was much stronger and there was no association with the mother's age.
Frans speculates that there may be a genetic link between the advancing age of the father and bipolar and other disorders in offspring. "As men age, successive germ cell replications occur, and de novo [new, not passed from parent to offspring] mutations accumulate as a result of DNA copy errors," Frans explains. The maternal side of the equation does not suffer such replication errors, she adds. "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."
Male Fertility Declines Markedly After 35
Older Sperm Behind Genetic Mutations
Older Fathers Risk Children With Schizophrenia
Source: Archives of General Psychiatry