The sperm age calculator tells men how decrepit their sperm are

By Jessica Hamzelou

A sperm age calculator can tell men how “old” their sperm are based on cues from DNA analysis and has revealed some of the effects of smoking on sperm.

Although a woman’s age has long been known to affect the health of her offspring, it is only recently that we began to understand how a father’s age can have similar effects. It is known that older fathers pass more genetic mutations on to their children than older mothers. And children of older fathers are more likely to have autism and schizophrenia.

The hope is that we may be able to examine people and say, ‘Your sperm is really old’ and identify risks to the offspring, “says Tim Jenkins of the University of Utah.

Growing evidence suggests that older fathers may pass on health risks through epigenetic markings on the DNA in their sperm. These tags alter the activity of active genes, and lifestyle factors such as diet and smoking are known to cause epigenetic changes that can affect the next generation.

Aging is also a factor. Jenkins and his colleagues examined the sperm of 350 men and looked for these genetic switches. So far, the team has found changes at 147 points in the genome that are related to a man’s age.

With this information, the team created a “calculator” that assesses the condition of the DNA of a man’s sperm at these 147 locations. Their analysis can predict a man’s age with approximately 95 percent accuracy and determine whether a man’s sperm has aged prematurely.

Jenkins and his colleagues found that smokers have much older-looking sperm. “For a 40-year-old man who smokes, our calculator would calculate him to 44 or so,” says Jenkins, who will present his results at the American Society of Reproductive Medicine annual meeting in San Antonio, Texas later this month.

Researchers don’t yet know whether these changes are responsible for the increased risk of autism and schizophrenia in children of older men, but Michael Carroll of Manchester Metropolitan University, UK, suggests it is.

“The emphasis on smoking has always been on the mother’s side,” says Carroll. “But it’s becoming more and more apparent that exposure in men can change health. It’s not just about how sperm swim or what they look like – there are changes at the molecular level that can affect offspring.”

Since sperm is produced throughout a man’s life, there is a chance that men with old sperm can reverse some of the damage, says Carroll.

“If you have a guy in his thirties or forties who is sperm age in his fifties or sixties, you need to look at why that is,” says Carroll. “If you could change these factors, you could possibly turn the clock.”