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Scientists have successfully used a new technique to identify the genetic mutation that causes sickle cell anemia. For the first time, preimplantation genetic diagnosis (PGD) has resulted in the birth of healthy twin girls to a couple where both partners were carriers for the sickle cell trait. The results of this study by researchers from The Center for Reproductive Medicine and Infertility (CRMI) at Weill Medical College of Cornell University and the New York Presbyterian Hospital (New York Weill Cornell Center), in conjunction with researchers at the Center for Molecular Medicine and Genetics (CMMG) at Wayne State University, appear in the May 12th issue of the Journal of the American Medical Association (JAMA).

Embryo biopsy by PGD is a diagnostic technique that is used with in vitro fertilization (IVF) to determine the genetic status of preimplantation embryos. PGD requires the expertise of highly skilled medical and genetic teams and is only available at specialized centers like New York Weill Cornell.

"This technique allows parents to know, with reasonable certainty, that their child will be normal before the mother is carrying the child. With this new capability, we can help couples who carry the genetic trait that causes sickle cell anemia, and we can virtually eliminate the risk of passing on that trait to their children," said Dr. Zev Rosenwaks, Principal Investigator of the study and Director of CRMI at New York Weill Cornell Center.

Sickle cell anemia affects nearly one in 625 births in African-Americans, although nearly 10% of patients with various sickling disorders are identified as non-African-American. Sickle cell disease is a condition which alters the shape of the red blood cells from round to "sickle" shape, causing them to block small blood vessels and interfere with normal blood flow. Children affected with sickle cell disease experience chronic episodes of pain and an increased susceptibility to potentially life-threatening conditions, including bacterial infections and organ failure. At the present time, there are no satisfactory treatments for this sickling condition.

Dr. Zev Rosenwaks and Dr. Kangpu Xu led the team of researchers at New York Weill Cornell Center in collaboration with Dr. Mark Hughes at CMMG. According to the report published in JAMA, the couple was treated in 1997 with standard IVF, a technique commonly used to treat infertility in which sperm and eggs are retrieved and fertilized in the laboratory. PGD was performed on the seven IVF-generated embryos and DNA analysis of single cells biopsied from these embryos determined the genetic status of each embryo. Three apparently normal, unaffected embryos were transferred back to the mother's uterus and a twin pregnancy was confirmed by ultrasound at seven weeks. Amniocentesis performed four months into the pregnancy confirmed that the twins were not affected with the sickle cell mutation. These healthy baby girls were delivered at the New York Weill Cornell Center on May 5, 1998.

"Our results confirm that PGD is a safe and viable option for couples who are carriers of sickle cell disease who wish to prevent a genetically defective child—it may provide them with a realistic alternative to prenatal testing," according to Dr. Xu, lead author of the study.

"PGD has already been used successfully to identify several other inherited traits including cystic fibrosis and sex-linked diseases such as hemophilia. This success is another indication that PGD has enormous benefits for couples who want to minimize the risk that they will pass on certain diseases or conditions to their children," Dr. Rosenwaks said. Previously, sickle cell anemia could only be diagnosed through amniocentesis, a procedure performed during pregnancy.

Currently at New York Weill Cornell Center, preimplantation genetic testing is offered to select couples who suffer from genetic disorders and chromosomal aberrations, including Tay Sach's disease, Down's syndrome, cystic fibrosis, thalassemia, and Fanconi's anemia among others. Drs. Rosenwaks, Xu and their colleagues are actively conducting research into the application of PGD for other chromosomal disorders such as Fragile X syndrome and Huntington's disease.