Dad's hidden influence: a father's legacy to a child's health may start before conception and last generations

Science News,  March 29, 2008  by Tina Hesman Saey

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Pregnant women know the drill. Don't drink. Don't smoke. Don't eat too much fish. Take vitamins. Mothers have long shouldered the responsibility, and the blame, for their children's health. Fathers don't usually face the same scrutiny.

How a man lives, where he works, or how old he is when his children are conceived doesn't affect their long-term health, scientists used to think. But growing evidence suggests that a father's age and his exposure to chemicals can leave a medical legacy that lasts generations.

Animal studies demonstrate that drugs, alcohol, radiation, pesticides, solvents, and other chemicals can lead to effects that are handed from father to son. Human studies are less clear, but some show that fathers play a role in fetal development and the health of their children.

Teenage dads face increased risk that their babies will be born prematurely, have low birth weight, or die at birth or shortly afterward, a new study in Human Reproduction shows.

Babies of firefighters, painters, woodworkers, janitors, and men exposed to solvents and other chemicals in the workplace are more likely to be miscarried, stillborn, or to develop cancer later in life, according to a review in the February Basic & Clinical Pharmacology & Toxicology.

Fathers who smoke or are exposed at work to chemicals called polycyclic aromatic hydrocarbons put their children at risk of developing brain tumors.

And, older fathers are more likely to have children with autism, schizophrenia, and Down syndrome and to have daughters who go on to develop breast cancer.

Though some of these observations are decades old, attitudes lag even further behind, says Cynthia Daniels, a political scientist at Rutgers University-New Brunswick in New Jersey. Dads aren't held accountable if something goes wrong during fetal development.

MATTER OF MATH Since men make new sperm every 74 days, people used to reason, the genetic slate is wiped clean every couple of months. And even if a man makes defective sperm, the "all-or-nothing" view of reproduction holds that damaged sperm don't fertilize eggs. No harm. No foul.

So no one bothers to remind men to protect themselves against environmental toxins. There are no images of "crack dads" and "crack babies" in the media like those of women who harm developing fetuses with drug and alcohol use, Daniels said in February at a meeting of the American Association for the Advancement of Science held in Boston.

When someone does study fathers-to-be, the focus is usually on fertility, not on the consequences for children's health, she says.

Yet even fertility messages meet resistance from many men.

Harry Fisch, director of the Male Reproductive Center and a urologist at Columbia University Medical Center, found that out when he suggested that men, like women, have ticking biological clocks.

Men can produce sperm throughout life, but that doesn't mean their cells are forever young.

"Every cell in the body ages," says Fisch. "Every cell. The older you get, the more chance of an abnormality. The same thing goes for sperm."

Men younger than 20 and older than 30 make more abnormal sperm than men in their 20s. These damaged sperm could create an unhealthy embryo or pass on damage that could lead to birth defects or illness in offspring.

It is not a popular message.

"Men do not want to hear this," Fisch says. "When my book came out, I got e-mails. I got faxes saying, 'How dare you say this? How can you say this? We know that there are men in their 70s having healthy children.'"

Despite these anecdotal accounts of elderly dads, studies demonstrate that older men are at increased risk of passing on genetic abnormalities. It's a matter of math.

Women are born with all the eggs they will produce in their lifetime. The cells that give rise to eggs divide 24 times, all before birth. But the cells that produce sperm continue to divide throughout a man's lifetime. Each year after puberty, a man's sperm-producing cells replicate about 23 times. Every time the cells divide is another chance for error.

As a result, the sperm produced by a 40-year-old man have gone through about 610 rounds of replication. That's 610 chances of introducing a mutation in the DNA, or improperly divvying up genetic material.

Parents over age 40 are six times more likely to have children with Down syndrome than 25-year-old parents, Fisch and colleagues showed in a 2003 study in the Journal of Urology. An extra copy of chromosome 21 causes Down syndrome. This extra chromosome is just as likely to come from dad as room in the older couples.

Older dads also have a higher risk of fathering children with rare mutations that cause dwarfism or a premature aging disease called Hutchinson-Gilford progeria syndrome.

But sometimes aging fathers pass along traits that can't be traced to only a single mutation. Fathers 40 and older have an increased chance that their children will develop complex disorders such as autism or schizophrenia. There is growing evidence that those disorders are caused by defects in many genes and the way genes are turned off and on.