TORONTO - Women injected with urine-derived fertility drugs could be at risk of developing the human form of mad cow disease, although no cases have yet been linked to the drugs, researchers say.
In a Canadian-led study, scientists for the first time document the presence of prion proteins in fertility drugs that are purified from the urine of postmenopausal women.
Prion proteins exist naturally in the body in a harmless form, but they can spontaneously alter their configuration to become "misfolded," making them infectious.
As infectious agents, prions can cause such transmissible and fatal neurodegenerative diseases as Creutzfeldt-Jakob disease (CJD) in humans and bovine spongiform encephalopathy (BSE), commonly known as "mad cow disease," in cattle.
More than 300,000 women in Canada and the United States are prescribed fertility hormones, including those purified from the urine of older women, an age when rare but deadly CJD most commonly occurs.
When the researchers examined dozens of urine-derived drug samples from various pharmaceutical companies and batches, they found evidence of prion proteins -- suggesting the drugs carry a previously unrecognized risk of contamination with the infectious agents.
So far, the danger is theoretical -- there has been no evidence of harm to women who have taken the drugs and it's not known how much of an actual risk they carry, said Dr. Neil Cashman, scientific director of PrioNet Canada and the study's co-principal author.
"There has never been a single recognized case of Creutzfeldt-Jakob disease in a woman who received these urinary pharmaceuticals," he stressed. "So that's a good thing. It means it's not common, if there is transmission. ... So if there's a risk, it's an extremely small one.
"That's a measure of reassurance -- but it's not a guarantee of safety," Cashman said Thursday from Vancouver, where he holds a Canada research chair in neurodegeneration at the University of British Columbia.
The authors of the study, published in the Public Library of Science (PLoS) ONE, say their findings suggest more prion-related research is needed on urine-derived fertility drugs.
Doctors should also think about using engineered products which were found to be prion-free, he said. Engineered, or recombinant, fertility drugs are produced in the lab using benign bacteria that have been genetically altered.
"Based on the information we now have -- including the detection of prions in urine of experimental animals, the relative ease of human-to-human transmission, the risk of prion infection through fertility drug injections, and the young age of fertility drug recipients -- it is important to consider whether the risks of these products may now outweigh their benefits," he said.
Calling it a well-done study, Dr. Roger Pierson said the findings are important.
"These are very sobering data and they should cause all of us to have a very deep reflection on what we know, what we think we know and how we apply that information to the health of Canadians and everyone else in the world," said Pierson, a spokesman for the Canadian Fertility and Andrology Society.
"The question is now we have the information, what to do. The reality is we need to say we understand this is a problem, look at techniques used to purify the products that come from urinary sources and understand the nature of the proteins in those drugs."
Pierson, a professor of obstetrics and gynecology at the University of Saskatchewan, said that will take collaboration between drug companies that make the products and regulatory bodies like Health Canada and the U.S. Food and Drug Administration.
"What we have right now is a very serious theoretical risk," he said from Saskatoon. "And as we learn more and more about prions and whether the prions detected in the drugs are actually infectious or are broken down parts of prions, those are all questions that need to be answered."
However, he said it would be dangerous to jump to rash conclusions without more research.
"This does not mean that every woman in Canada that's had these drugs is going to get sick, or even a small proportion of them. But we need to look."
