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Cystic Fibrosis Risk Found in Fertility Treatment
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By Adam Marcus Standard gene screening can miss mutation THURSDAY, June 10 (HealthScout) -- While infertility treatments have made parents out of people who otherwise couldn't conceive, there's been an unforeseen cost. Canadian scientists say screening tests are alarmingly ineffective when it comes to catching genetic triggers for cystic fibrosis in the sperm of clinically sterile men. The research, which will appear in next week's issue of the Journal of the American Medical Association (JAMA), was presented today at a genetics meeting in San Francisco. There seems to be a paradox here. How could a clinically sterile man pass on anything in his sperm, much less a genetic trigger for cystic fibrosis? The answer: New procedures have all but eliminated male infertility. Doctors can now fertilize an egg in the lab with a single, well-aimed sperm. Men who no longer had the means to sire now can. But at what price? Led by Dr. Keith Jarvi, associate professor of surgery at the University of Toronto, Ontario, the researchers studied 198 men with a type of infertility that meant they could make sperm but not send it anywhere. Two of the conditions involved the absence of one or both of the vas deferens, the set of tubes that guides sperm from the testes; another one involved unknown blockage of the epididymis, the tube where sperm are housed and mature. Jarvi's group tested the men for mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The standard CFTR test looks for between 30 and 70 of the most common mutations found in whites. But Jarvi and his colleagues found that, compared with a much more thorough screening test, the boilerplate "panel" missed between one-half and three-quarters of CF mutations in men. Cystic fibrosis is one of the most common genetic diseases, affecting as many as one-in-3,500 people in North America. All but eight percent are diagnosed before age three. The disorder leads to gumming of the airways with heavy mucus, problems in the pancreas, and a host of other ailments, and has been linked to at least 800 DNA mutations in its gene, the cystic fibrosis transmembrane conductance regulator. Another complication of cystic fibrosis is male infertility, frequently the result of malformations in the tubes that shuttle sperm from the testes to the penis. Now that the tube transmitting problem has been overcome, children born to these men have up to a 25-fold increased risk of developing CF if their mother also carries a mutation for the disease, the research shows. In addition, even children with only one bad gene are more likely to contract a mild form of the condition, leading to lung, sinus and pancreatic problems. Finally, says Jarvi, the stealthy mutations also increase the risk that male children will have fertility problems like their fathers. The message, says Jarvi who is also a staff urologist at Mount Sinai Hospital in New York City, is that men who come to fertility clinics with blocked or missing tubes should be given the more rigorous gene screening. The test can cost up to about $300, twice the price of the regular panel. What's more challenging, he admits, is how to use the information. Most parents who seek fertility help are desperate for children and won't be deterred by something as abstract as a risk factor, he says. "There's a wide spectrum of what risks patients are willing to take with their children," Jarvi says. Dr. Harry Fisch, director of the male reproductive center at Columbia-Presbyterian Medical Center in New York City, says the latest study shouldn't come as a surprise. "I think we're at the infancy in this fertility issue," says Fisch, who also holds a post at the Albert Einstein College of Medicine. "Today, we don't really have the tools for widespread use to detect these gene abnormalities. We are passing down genes that may have a problem." The trouble, he says, is that doctors, and families who benefited from fertility therapy, won't know the extent of the risks for a decade or more, when the earliest generation of intracytoplasmic sperm injection babies matures. "It's really one big experiment," says Fisch. What To Do Forunately, says Fisch, most children born through infertility treatments turn out fine. While significant, this study tested only 198 men. Many gene diseases require two sets of abnormal DNA, so even if the father's sperm is damaged, a clean copy of genetic information from the mother is sufficient to create a normal offspring. On the other hand, Fisch says, it's imperative that parents considering infertility treatments like the single-sperm injection be fully aware of the potential dangers, and that they get screened for known gene defects. "Most people will continue on with this understanding that this is still an experiment," Fisch says.
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