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July 22, 2005 -- Scientists may have a new lead on a source of women's infertility.
They studied a gene tied to the hormone estrogen. The gene governs estrogen receptor beta, a protein involved in estrogen's effects.
Estrogen works on tissues by binding to a part of cells called estrogen receptors. There are two types of estrogen receptors found throughout a woman's body.
Mice lacking the estrogen receptor beta had reduced fertility and were less responsive to fertility drugs than normal mice, the researchers report in Endocrinology.
Future Infertility Blood Test?
It's not yet known if the same holds true for women. If so, a blood test could screen for the genetic mutations that affect the estrogen receptor function, giving women more information about their response to fertility treatment options.
That's according to a news release from the National Institute of Environmental Health Sciences (NIEHS), which conducted the study. The NIEHS is a branch of the National Institutes of Health (NIH).
Helping Couples Cope
The goal of such a blood test would be to give couples facing infertility a better sense of their situation.
"Dealing with infertility can be emotionally, financially, and physically draining," states NIEHS director David Schwartz, MD, in the news release.
"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 safe and healthy child," Schwartz continued.
The study doesn't blame genetics for all infertility.
About the Study
Some mice used in the study were bred to lack the estrogen beta. They were compared with healthy mice.
The mice got fertility drugs to stimulate egg development and ovulation, like those commonly given to women undergoing fertility treatments.
Despite the drugs, the mice lacking the beta receptor were more infertile than healthy mice, write Kenneth Korach, PhD, and colleagues.
"What we found is that the beta estrogen receptor plays a role in moving the egg outside the ovary so it can be fertilized," states Korach, in the news release. "We never knew before what function this receptor played in reproduction."
Tracking Fertility in Mice
Eggs are stored in the ovaries. They are released into the reproductive system to be available for fertilization. A mix of hormones is involved in that process.
In mice lacking the estrogen receptor beta, egg development within the ovary was on average less than 30% that of normal mice.
With a higher dose of the fertility drugs, some (but not all) of the mice lacking the beta receptor yielded more eggs. Still, they didn't equal levels seen in normal mice.
Despite the fertility drugs, some of the mice lacking the beta receptor did not ovulate at all. They had no pregnancies over several months.
Other mice were "subfertile." They had a normal number of pregnancies but with fewer baby mice per pregnancy than normal.
SOURCES: Couse, J. Endocrinology, August 2005; vol 146: pp 3247-3262. News release, National Institute of Environmental Health Sciences. WebMD Medical Reference from Healthwise: "Infertility: Cause."