New York, NY (May 12, 1999) - 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.
