Wednesday, May 30, 2007

The number of men ages 35-49 who father children has increased 40 percent since 1980 while the number of fathers under 30 has fallen 20 per cent

Research finds sperm quality drops, genetic problems rise as men age
Sabin Russell, Chronicle Medical Writer

Tuesday, June 6, 2006

With a lineup of Bay Area men at their disposal, Lawrence Livermore scientists have deflated yet another cherished male fantasy -- that sperm quality resists the ravages of age.

In fact, the genetic quality of sperm deteriorates as time goes by.

The Livermore analysis of sperm samples from men ages 22-80 found a gradual but steady increase in the percentage of genetic mutations over time, raising the risk of infertility and of fathering children with genetic abnormalities.

Until now, men had some reason to think their sperm could stand the test of time: Sperm are generated continuously in the testes from sexual maturity through old age. A woman's supply of eggs, on the other hand, is produced before birth. Because the eggs age with her, the risk for some chromosomal anomalies such as Down syndrome linked to egg defects increase with a pregnant woman's age.

The study found that although an older man's sperm does not increase the likelihood of Down syndrome, other genetic conditions such a dwarfism can be passed on with greater frequency by older men.

"There is a reproductive consequence to delaying fatherhood,'' said Andrew Wyrobek, a senior staff biophysicist at the Livermore National Laboratory, and lead author of the study published today in the Proceedings of the National Academy of Sciences.

It is an issue of increasing relevance as men as well as women defer parenthood to a later age in the United States. The number of men ages 35-49 who father children has increased 40 percent since 1980, according to Wyrobek, while the number of fathers under 30 has fallen 20 percent. .................................

Co-lead author Barbara Eskenazi said: "We know that women have a biological time clock. Our research suggests that men too have a biological time clock - only it is different. Men seem to have a gradual rather than an abrupt change in fertility and in the potential to produce viable healthy offspring."

But it found a steady increase in the amount of broken DNA strands as the age of the subjects increased. This genetic damage can translate into fertility problems, pregnancy failures and an increase in some genetic diseases.

As the men aged, the researchers found that the number of genetic mutations that can cause dwarfism increased in the sperm with the age of the men -- at a rate of about 2 percent per year.

Wyrobek stressed that, although the trend toward genetic deterioration with age was clear, there were disparities in sperm quality among the men within each age group. Even in the oldest cohort, there were some men with few genetic mutations in their sperm, while others had multiple abnormalities.

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