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Size Matters

Canadian researchers discover mechanism that controls size of human eggs

OTTAWA, November 25, 2003 - In a discovery that could lead to improved treatment of infertility and higher success rates for In Vitro-Fertilization (IVF), researchers at the Ottawa Hospital Research Institute have identified the mechanism that controls size in eggs and early embryos, including human eggs.

While scientists have known for some time that the size of the human egg is a prime determinant in the viability of the reproductive process, to date any attempts made in a laboratory setting to maintain the precise size of egg required for proper development have been made by trial and error.

"When treating infertility, eggs are very often fertilized in a clinic in the process known as IVF," says Dr. Jay Baltz, a Senior Scientist at The Ottawa Hospital Research Institute. "It was understood that one of the secrets for getting eggs that would be healthy and would develop as normal embryos out of this process was to adjust conditions so that their size stayed as close to normal as possible during the time they were growing in the laboratory, before being returned to the mother's uterus. However, we didn't know anything about how the size of the egg was controlled, and so adjusting the conditions was always done by trial and error."

The discovery made by Dr. Baltz and his team, however, virtually eliminates this kind of guesswork, something which carries significant implications for those suffering from infertility. "We've known for a while that eggs and very early embryos contain a large amount of one particular small molecule - the amino acid glycine," Baltz explains. "Our research team has now found that it is this glycine which controls the size of eggs and early embryos, and we have identified the mechanism that the egg uses. We found in our study that when fertilized eggs and early embryos were able to control their size using this mechanism, they remained healthy and grew normally. However, if this was prevented, then we found that the embryos failed to develop."

According to Dr. Baltz, this information was a missing link in knowing how to improve the success rates of IVF, in which only 10-20% of eggs currently go on to produce pregnancies. "Knowing how growth occurs within eggs and early embryos will allow physicians to better treat infertility by designing better conditions for IVF," stated Dr. Baltz. "Overall, these findings will allow us to understand more completely how healthy embryos develop, which is a very important step in treating infertility."

Led by Dr. Baltz, the group's study results are released in this month's publication of the prestigious Proceedings of the National Academy of Science (PNAS). The group's work is made possible thanks to generous support from the Canadian Institutes of Health Research (CIHR).

About the Ottawa Hospital Research Institute

The OHRI is an institute of The Ottawa Hospital and University of Ottawa. With more than 200 scientists, 225 students and more than 400 support staff, and $47 million in external funding, the OHRI is one of the fastest growing and most respected hospital-based research institutes in Canada.

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