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CNN's Rhonda Rowland reports on pre-implantation genetic diagnosis
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May 12, 1999
Web posted at: 11:33 a.m. EDT (1533 GMT)

NEW YORK (CNN) -- A New York-area couple who are both carriers of sickle cell disease have twin babies who are completely free of the sickle cell gene, thanks to a technique called pre-implantation genetic diagnosis (PGD), in which fertilized embryos are tested for the disorder before implantation in the woman's uterus.

This first successful use of PGD to eliminate sickle cell disease was reported in Tuesday's Journal of the American Medical Association.

One of every 625 babies born to African-Americans has the blood disorder, which causes repeated episodes of severe pain, and a lowered life expectancy.

The 34-year-old woman who successfully gave birth to the healthy twins had already had two abortions because the fetuses were affected with sickle cell anemia. The lead author of the JAMA report, Kangpu Xu, Ph.D., of Weill Medical College, wrote that the couple then went through extensive counseling and decided to try PGD.

On the second try at in vitro fertilization, doctors tested seven embryos for the sickle cell gene. Four were normal, two were carriers, and diagnosis was unclear for one embryo.

Three disease-free embryos were implanted, and the woman gave birth to healthy twins after 39 weeks of pregnancy.

Genetic test of embryos still experimental

Xu and his colleagues at Cornell University in New York stressed that the PGD test was still experimental in looking for single gene defects, such as sickle cell disease. But with further refinement, researchers said, it will become a powerful diagnostic tool.

Tests already exist to check a fetus for sickle cell during pregnancy. But some couples have strong personal objections to abortion when a pregnancy is already established. Pre-implantation genetic diagnosis could provide couples with another way to avoid passing on sickle cell disease.

When both parents are carriers, they face a 25 percent chance of having a child with the disease, and half of their children may carry the gene. Sickle cell is a blood disorder that affects people of African heritage and several other ethnic groups from around the Mediterranean region.

People with the disease have recurring episodes of intense pain; an increased susceptibility to infections, strokes and organ failure; and a lowered life expectancy.

Cost may be an issue

Despite the success of PGD testing, Xu and his co-authors suggested that its high cost may limit how widely it can be used. And the in vitro fertilization procedure itself is fairly expensive.

Beyond sickle cell anemia, several other hereditary diseases can be diagnosed in an embryo using PGD, including Tay-Sachs disease, Down's syndrome, cystic fibrosis, thalassemia and Fanconi's anemia. And researchers hope soon to add Fragile X syndrome and Huntington's chorea to the list of illnesses that can be detected in a human embryo.

Medical Correspondent Rhonda Rowland contributed to this report.