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PGD, or preimplantation genetic diagnosis, is a new technique, which marries the recent spectacular advances in molecular genetics and assisted reproductive technology. Preimplantation genetic diagnosis enables physicians to identify genetic diseases in the embryo, prior to implantation, before pregnancy is established. PGD was first developed for patients who were at risk of having children with serious genetic disorders, which often discouraged them having their own biological children. These couples are often faced with attempting a type of "Russian Roulette" to have children, many times having to confront the difficult decision to terminate an affected pregnancy.
Consider a woman known to be carrying an X-linked disease such as hemophilia with a 50% risk of an affected male in each pregnancy. Her daughters have a 50% risk of being carriers, but are unlikely to be clinically affected. She may not wish to become pregnant if she has to make decisions about an affected child in a viable pregnancy. However, she would become pregnant if she knew she had conceived a daughter, and with preimplantation diagnosis this possibility becomes a reality. PGD thus eliminates the need for possible pregnancy termination after prenatal diagnosis of a genetically affected fetus.
Research has shown that it is possible at three days after fertilization to remove one or two cells from an 8-10 celled embryo without affecting its further development. Embryos can be sexed on the basis of the presence or absence of a DNA fragment specific for the Y chromosome and in 1990 two sets of twin girls were born to five couples at risk of passing on an X linked disorder. Subsequently, a number of babies have been born after preimplantation genetics has ruled out the diagnosis of a number of genetic diseases such as cystic fibrosis, Tay Sachs disease and Lesch Nyhan syndrome.
Sexing the embryo to avoid X linked diseases such as hemophilia and duchenne muscular dystrophy remains the commonest reason for preimplantation diagnosis, now optimally carried out by the molecular cyto genetic technique of FISH (fluorescent in situ hybridization) with DNA probes derived from the X and Y chromosomes.
© Dr. Aniruddha Malpani and Dr. Anjali Malpani www.drmalpani.com
Credits: How to Have a Baby: Overcoming Infertility
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