|
| |
Preimplantation
Genetic Diagnosis Preimplantation genetic
diagnosis (PGD) allows the embryologist and physician to screen embryos
for certain inherited genetic diseases. These diseases include Fragile
X Syndrome, Sickle Cell Anemia, Tay Sachs, Cystic Fibrosis, Hemophilia,
Thalassemia, and others. Each cell in the body,
and in an embryo, contains the full genetic blueprint of a person and
the chromosomes can be examined for abnormalities. Therefore, some genetic
diseases can be identified by examining the chromosomes in an embryonic
cell.
Once an embryo has
fully matured and is ready for transfer, a small hole is made in the outer
membrane (zona pellucida) using acid Tyrode's solution, a needle, or a
laser and a single cell is withdrawn. The embryo is not damaged by this
process and will develop normally.
The chromosomes are
analyzed using a process known as fluorescent in situ hybridization (FISH)
and the polymerase chain reaction. The polymerase chain reaction "amplifies"
or "duplicates" sections of the chromosome allowing exami nation
of specific segments. Some diseases are
"sex linked" meaning they are contained on the X or Y chromosome.
Hemophilia is carried on the X chromosome and a mother with the disease
or who is a carrier of the gene abnormality has a very high probability
of passing it to a male child. Diseases such as Down's syndrome are caused
by an extra chromosome (chromosome 21).
After PGD, only embryos
that are not carrying the genetic disorder are transferred into the uterus.
Many researcher hold great hope that advances in PGD will allow for the
screening of other diseases and identify embryos that are at high risk
for miscarriage.
|
|
