Fertility drugs may not help certain women if they lack a certain estrogen-related gene, scientists, who studied mice, report on Wednesday.

Mice genetically engineered to lack the gene did not ovulate in response to fertility drugs, the researchers found. If the same is true in women, it could help explain some forms of infertility and also help steer women away from treatments unlikely to help them.

The gene is called estrogen receptor beta, the team of National Institutes of Health researchers report in the August issue of Endocrinology.

“What we found is that the beta-estrogen receptor plays a role in moving the egg outside the ovary so it can be fertilized,” Kenneth Korach of the National Institute of Environmental Health Sciences (NIEHS) said in a statement. “We never knew before what function this receptor played in reproduction.”

The NIEHS researchers treated normal female mice and genetically engineered mice with fertility drugs similar to those commonly used by women undergoing fertility treatments.

The mice bred to lack this receptor gene were more likely to be infertile or had fewer offspring. When treated with fertility drugs the mice did not produce more egg cells.

“Dealing with infertility can be emotionally, financially and physically draining,” said Dr. David Schwartz, director of the NIEHS.

“If we can help couples understand the reasons for their infertility, doctors can further define their treatment options, help them to minimize the expense and risk of taking drugs that may be less effective for them, and increase their chances of having a…healthy child.”

The NIEHS may also try to find out whether defects in estrogen receptor beta are inherited or caused by some environmental effect - and whether perhaps diet can alter the defects.

Estrogen receptor beta is known to respond to environmental and dietary chemicals that can mimic the effects of estrogen and stimulate the body’s natural hormones, such as genistein, a compound found in soy products, the NIEHS said.