EXHAUSTED GENES: A recent study found that asthma was more common among New York City children exposed in the womb to high levels of a pollutant found in car exhaust.
FLICKR/KEVIN COLES

Each of us starts life with a particular set of genes, 20,000 to 25,000 of them. Now scientists are amassing a growing body of evidence that pollutants and chemicals might be altering those genes—not by mutating them, but by sending subtle signals that silence them or switch them on at the wrong times.

Last week, several dozen researchers and experts convened by the National Academies tackled this complicated topic, called epigenetics, at a two-day workshop in Washington, D.C. They discussed new findings that suggest chemicals in our environment and in our food can alter genes, leaving people vulnerable to a variety of diseases and disorders, including diabetes, asthma, cancer and obesity. They also considered whether regulatory agencies and industry should start testing the thousands of chemicals in use today for these effects.

“There is little doubt these epigenetic effects are important. The next question is how we test for effects," said William H. Farland, professor of environmental and radiological health sciences at Colorado State University. "We don’t need to abandon current approaches to chemical testing. When testing chemicals in animals, we may just need to add some new endpoints."

Exposure to gene-altering substances, particularly in the womb and shortly after birth, “can lead to increased susceptibility to disease,” said Linda S. Birnbaum, who was named director of the National Institute of Environmental Health Sciences and of the National Toxicology Program in December. “The susceptibility persists long after the exposure is gone, even decades later. Glands, organs, and systems can be permanently altered.”

“There is a huge potential impact from these exposures, partly because the changes may be inherited across generations. You may be affected by what your mother and grandmother were exposed to during pregnancy,” Birnbaum said.

What a pregnant mother eats and the chemicals she is exposed to can affect her offspring without causing mutations in the DNA, the experts said. Instead, such exposures can disrupt the way that genes behave, according to both animal and human studies. These changes, in turn, can be passed on to the next generations.

Some environmental chemicals enable methyl groups (carbon atoms with three hydrogen atoms attached) to attack genes, which turns them off or mutes them, at a time when they should be turned on. When genes are turned off, they can’t direct the manufacture of proteins that are essential for proper cell function. Chemicals also can uncoil parts of the chromosome, causing genes to be expressed, or turned on, at inappropriate times.