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Medicine: The Sins of the Fathers

6 minute read
Andrew Purvis

Ever since thousands of severely deformed babies were born in the early 1960s to mothers who had taken the drug thalidomide, doctors have been alert to the risks that certain chemicals can pose to developing fetuses. Precautions, however, have been based on one central assumption: that exposure to dangerous substances is most likely to occur inside the wombs of mothers- to-be. A series of studies has raised the possibility that the fault can sometimes lie with the father. Poisons in a man’s body may silently damage his sperm and thus lead to birth defects.

The new research suggests that men exposed to substances such as lead, alcohol and some anticancer medications, as well as nuclear radiation and dioxin-containing herbicides, could be conceiving children with serious physical and mental abnormalities. Although the reports do not prove that such damage is occurring, the increasing number of studies reflects a concern about the issue that some experts feel is long overdue. Says Dr. Ellen Silbergeld, a toxicologist at the University of Maryland: “There has been a sense ((among scientists studying birth defects)) that reproduction is something that women do, and that men don’t contribute very much. That is simply not true.”

Researchers have long known that certain poisons can produce so-called dominant lethal effects in men. In these cases, the sperm is so damaged that it fails either to fertilize the egg or to produce a viable embryo. But little was known about whether toxins could trigger more insidious defects in the sperm — problems subtle enough to allow the birth of the child but still harmful enough to produce serious malformations. Perhaps the most disturbing recent report concerns lead, which had been shown to impair fetal growth when mothers were exposed while pregnant. At a meeting last month of the American Public Health Association, Silbergeld reported on a study in which male rats subjected to even low levels of the toxic metal — comparable to amounts found in the dust and dirt of many inner-city neighborhoods — often sired offspring with “substantial” changes in brain development.

The dangers of nuclear radiation have been exhaustively studied, especially among survivors of Hiroshima and Nagasaki. Yet researchers had never confirmed that the children of exposed men could be affected. Earlier this year, researchers in England reported that such transmission may in fact be possible. Children of male workers at the Sellafield nuclear power plant were up to eight times as likely to be stricken by leukemia as children whose fathers did not work at the plant. The researchers theorized that cumulative low-level doses of radiation during the six months before conception may have triggered the damage.

Vietnam veterans have long contended that the herbicide Agent Orange, which contains dioxin, has contributed to birth defects in their children, although scientists have not been able to confirm the link. Still, a patchwork of reports continues to suggest at least a minor effect. The most recent study, published last month in the American Journal of Public Health, found that the children of men who served in Vietnam were 1.7 times as likely as the babies of other veterans to suffer from major malformations, such as clubfoot or serious heart problems.

The list of substances suspected of harming children through their fathers is growing steadily. One preliminary report concluded that heavy drinking by a man in the month before conception could cause his child to have low birth weight. Another study conducted in rats found that a powerful anticancer agent called cyclophosphamide — used primarily against advanced malignancies — could hamper nervous-system development in some offspring. Scientists have also begun a major examination of the U.S. semiconductor industry, where workers come into contact with numerous chemicals. The researchers will be looking for birth defects in children of male, as well as female, employees.

Just how men might pass health problems on to their offspring is unclear. In women it is easy to see how substances, once they enter the bloodstream, can penetrate the placenta and harm the fetus, but in men the mechanism must be more complicated. Whatever problems are transmitted have to be passed on ! through the sperm or seminal fluid only at the time of intercourse. Still, researchers believe this could happen in several ways. A toxin might directly damage the genetic material within the sperm (but not so much as to prevent fertilization). Or the poison could alter the packaging around the DNA and somehow hamper the process by which it is unfolded and combined with the egg. Finally, chemicals contained in the semen could pass directly into the women and damage the egg or part of the reproductive tract. Most experts concede, however, that these mechanisms are speculative. Notes Dr. Jeanne Stellman of Columbia University’s School of Public Health: “The big question remains, Do funny-looking sperm produce funny-looking babies? We don’t have an answer to that.”

The issue has caught the attention of women’s groups. Many have been angered by what they consider an overemphasis in science and the media on the woman’s role in triggering birth defects. These critics are particularly concerned about the so-called pregnancy police — a growing band of fetal-rights groups and policymakers who want to regulate women, punishing those who are not properly caring for unborn babies.

In a case before the Supreme Court, Johnson Controls, a Milwaukee-based company, is trying to bar fertile women from the assembly line at a car- battery plant because of alleged risks that such work may pose to unborn children. If the court decides in favor of the company, solid evidence that men are also endangering their future children could lead to major legal challenges as well as a thorough re-examination of procedures in U.S. factories.

No one is suggesting that scientists abandon their search for potential problems in pregnant women. But that approach alone is unlikely to clear up all the questions surrounding the 250,000 birth defects that occur in the U.S. each year. The origins of 60% of these defects are still unknown. Any research that could dispel some of the disturbing mystery behind those numbers would be welcomed by mothers and fathers alike.

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