Some couples are at increased risk for transmitting genetic diseases to their children. The disorders include hemophilia, Tay-Sach's disease, Sickle Cell Anemia, Cystic Fibrosis, Down's syndrome, and others.
Women over the age of 38 or those with recurrent miscarriage may be at risk for chromosomal abnormalities called aneuploidies. Preimplantation Genetic Diagnosis (PGD) allows the embryologist to screen embryos for these and many other genetic abnormalities.
PGD patients undergo in vitro fertilization to create embryos that will be transferred to the uterus. Once the embryos mature, the embryologist makes a small hole in the embryo's outer membrane using a laser. A single cell is withdrawn for the PGD procedure(s) without damage to the embryo. Each cell contains the complete genetic makeup of the embryo.
The cell is examined for an abnormal number of chromosomes, using fluorescent in situ hybridization (FISH). FISH, enables the embryologist to count chromosomes and often identify other abnormalities.
The polymerase chain reaction (PCR) is used when damage, or disease, is suspected on a particular chromosome segment. The PCR duplicates and amplifies certain chromosome sections so that disorders can be seen.
Some diseases, such as hemophilia, are sex-linked meaning they are transmitted on the X chromosome. Because males have only 1 X chromosome but females have 2, these sex-linked diseases are more apparent in males. Hemophilia is an example of a sex-linked disease, meaning that males are the ones usually affected. FISH can be used to separate male and female embryos, and in this case, only female embryos would be transferred to the mother. The same applies if a chromosomal abnormality is seen using PCR in that only normal embryos would be transferred.
While no procedure is guaranteed to eliminate birth defects, there are many genetic diseases that can be identified using PGD and research continues to expand the list. Using PGD lowers the chances of genetic birth defects.
