Genetic Quality of Sperm Deteriorates as Men Age
Defects heighten risks of disorders such as schizophrenia and dwarfism, study suggests
TUESDAY, June 6, 2006 (HealthDay News) -- A pioneering study has found specific genetic defects in the sperm of older men.
The results suggest that, like women, some men who wait to become fathers raise the risk of passing on certain diseases to their children.
But Andrew J. Wyrobek, lead author of the report and a senior medical biophysicist at the Lawrence Livermore National Laboratory, in California, cautioned that the findings are preliminary because the study was based on just a few tests, one of them developed as recently as this year.
Still, the discovery has endless possibilities, he added.
"This opens up a whole line of research," Wyrobek said. "We have looked at a few genes out of many hundreds. We need tests for those other genes to look at their function as affected by age."
The findings appear in this week's issue of the Proceedings of the National Academy of Sciences.
It has been known that offspring of older fathers are more likely to suffer from conditions such as schizophrenia and achondroplasia, a form of dwarfism, the journal report said. The study enlisted 97 men, aged 22 to 80, from two locations -- the Livermore, Calif., area and Baltimore, the home of Johns Hopkins University, whose researchers participated in the trial.
Many of the findings found no link between birth defects and the sperm of older men. For instance, there was no increase in the incidence of multiple or missing chromosomes that cause Down syndrome and several other genetic conditions. But there was an increase in gene mutations that can lead to achondroplasia and Apert syndrome, which causes malformation of the skull.
Conventional measurements of sperm quantity, such as sperm count and mobility, were not related to the genetic abnormalities, the researchers found.
One intriguing discovery involved a difference in some of the genetic defects, depending on where the men lived. The California group consisted largely of middle-class whites, while the Baltimore group included many inner-city residents. "In the inner city people from Baltimore, we found an age effect that we did not find in California," Wyrobek said.
That finding, he said, "raises the question of whether things that affect the aging process differ among people with different backgrounds, such as income," he said.
Dr. Ethylin Wang Jabs, a professor of pediatric genetics at Johns Hopkins and a member of the research team, said, "We think some of the mutations or changes we are studying could be caused by environmental effects."
There might also be an economic cause for the differences, Jabs said, "but I would be cautious about this because our numbers were small."
The study could help resolve a running debate about the effect of age on the genetic quality of sperm, Wyrobek said. "There have been some studies here or there that look at a single endpoint," he said. "In one person they might find a change, in the next person they might not find it."
What the study shows is that as they grow older, "a small fraction of men are at risk for transmitting multiple genetic and chromosomal defects," the report concluded.
For more on birth defects, visit the March of Dimes.