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Genetic Breakthrough in Sickle Cell Anemia
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By Edward Edelson Test allows disease-free kids, avoids abortion TUESDAY, May 11 (HealthScout) -- Combining two biomedical technologies, doctors and scientists have enabled a man and wife who carry the gene for sickle cell anemia to have babies free of the life-shortening genetic disorder. The key to the achievement was a preimplantation genetic diagnosis (PGD), a gene study to determine whether fetuses conceived through in vitro fertilization have the genes for sickle cell anemia. It is the first time that PGD has been used for that purpose, says a report in the May 12 Journal of the American Medical Association by a team from Cornell University's Weill Medical College in New York City. Sickle cell anemia occurs mostly in African-Americans, 8 percent of whom carry one gene for the disorder. The gene has persisted in warm-weather countries in Africa and elsewhere. A single copy of the gene, which protects against malaria, usually causes no symptoms. However, a baby born with two copies of the gene is susceptible to infection and many life-threatening conditions. The disease has no effective treatment. Until now, the only way to avoid birth of a sickle cell child was to have amniocentesis and genetic testing during pregnancy and to abort the fetus if it carried two flawed genes. PGD makes it possible to avoid an abortion, said Kangpu Xu, an assistant professor of obstetrics and gynecology and a key member of the Cornell team. "In the world, there are a few major medical centers doing it," Xu said. "This is a very new technique." The Cornell team worked with a 34-year-old woman, who previously had two abortions because she was carrying fetuses with sickle cell anemia. The first step was in vitro fertilization, in which her eggs were fertilized in the laboratory. The first in vitro attempt produced no fetuses. A second try resulted in seven embryos. PGD showed four were normal and two were carriers; diagnosis was not possible for the seventh. Three of the normal embryos were implanted. To be sure of the initial findings, amniocentesis was done during the pregnancy. Healthy twins were delivered after 39 weeks. The obstetrician was Dr. Zev Rosenwaks, director of the Center for Reproductive Medicine and Infertility at Cornell. The Cornell team has since made another attempt, but the patient did not become pregnant. Other attempts will be made, Xu said. While the procedure is both complex and expensive, it is better than the alternative of giving birth to a child with the disease, he said. "The second a child is born, it is in danger," Xu said. "Right now there is no satisfactory treatment. Marrow transfer, blood transfer -- none of the treatments is effective." The journal article said "although prenatal testing is currently available, some couples have strong personal objections to aborting affected fetuses. For these couples, PGD provides a realistic alternative to prenatal testing." Cornell also offers PGD for couples with other genetic conditions, including Tay-Sach's disease, cystic fibrosis and thalassemia. Cornell and other medical centers are working to use PGD with other conditions. What To Do Couples who carry the gene for sickle cell anemia should consult their physicians. The combination of in vitro fertilization and PGD is still experimental. "We want to make sure that the technique works. At this stage, we still cannot recommend it," Xu said.
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