A new study has found that babies born to men with birth defects are themselves twice as likely to have birth defects, compared to the offspring of other fathers. Intriguingly, the findings, published today in the Journal of the American Medical Association, indicate that children of affected fathers are at a higher risk of all kinds of defects, not just the one their father had.

Allen J. Wilcox of the National Institute of Environmental Health Sciences and his colleagues studied 12,000 men who had been born with a recognized defect, such as cleft lip or clubfoot, and compared them with nearly half a million unaffected men. Whereas the total risk of birth defects amounted to 2.1 percent among babies born to the unaffected men, those born to men with defects had a 5.1 percent risk.

What really stood out in the data was the range of defects these infants exhibited: 3.4 percent of the children born to affected fathers had defects that were unlike that of their parent. Considering that many birth defects are heritable, the team had expected more of the babies' defects to match their father's. Indeed, an earlier study of women with birth defects found that their children only showed an increased risk for the mother's defect. At present the authors do not have an explanation for the skew in the new study.

"We also need to put this into perspective," Wilcox remarks. "More than 95 percent of all babies with birth defects are born to parents who have no known birth defects themselves. Measles, a lack of folate in the diet and heavy alcohol use are factors for some defects, but the causes of most birth defects--environmental as well as genetic--are not known. We have a lot to learn, still, about the cause and prevention of birth defects."