Senior sperm have dodgier DNA
Men, prepare to hear the ticking of your biological clock
Women who gnash their teeth at men's lack of a biological clock can now take cold comfort from a survey of DNA in sperm, which has found that genetic defects can crop up as men age, potentially diminishing their fertility.
Nearly 100 men aged 22 to 80 who worked at the Lawrence Livermore National Laboratory in California, each donated a semen sample for the study. The samples were then videotaped, counted and tested at the nearby University of California, Berkeley.
Compared to their younger colleagues, the oldest men had five times as many sperm with high levels of fragmentation in their DNA, which is associated with infertility. Sperm from older men were also more likely to carry a mutation that causes achondroplasia, the most common kind of dwarfism.
But there was no age-related effect on the damage that causes Down's syndrome, which is quite closely associated with the mother's age. The study is published this week in the Proceedings of the National Academy of Sciences1.
Don't delay, breed today
People are increasingly choosing to delay parenthood, says Brenda Eskenazi, an epidemiologist at Berkeley, and one of the lead investigators on the project. "Men need to consider not just the female's fertility, but their own, and not just their fertility but their ability to produce healthy offspring." She adds that effects of age on many possible genetic abnormalities of sperm remain to be tested.
Routine semen analysis counts the number, mobility and shape of sperm. But standard tests do not look for DNA fragmentation or the achondroplasia mutation.
Craig Niederberger, a urologist at University of Illinois at Chicago, says the results are interesting, but adds that he is cautious about measurements of DNA fragmentation. Some previous research has not found DNA fragmentation to be directly associated with pregnancy outcomes in a fertility clinic2.
"Up until recently, when we had only semen analysis to guide us, it appeared that male reproductive potential was stable through life," Niederberger says. "Now that we have tools to investigate sperm DNA, we are beginning to see potential effects in ageing, but I wouldn't say that they are conclusive."
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- Wyrobek A. J. , et al. Proc. Nat. Aacd. Sci, published online doi:10.1073/pnas.0506468103 (2006).
- Payne J., et al. Fertil Steril., 84. 356 - 364 (2005).
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