Genetic Diagnosis For Single Gene Disorders And Structural Chromosomal Abnormalities

Genetic Diagnosis For Single Gene Disorders And Structural Chromosomal Abnormalities

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Preimplantation genetic diagnosis (PGD) is a test that aims to diagnosis for single gene disorders and structural chromosomal abnormalities (Sermon & Viville, 2014) in human embryos prior to implantation for couples at risk of transmitting genetic disorders to their offspring. PGD has its roots in the sexing of farm animals for selective breeding purposes (Braude, Pickering, Flinter, & Ogilvie, 2002). The first account of preimplantation testing was in 1968, during which Gardner and Edwards of the University of Cambridge, in The United Kingdom, successfully determined the sex of cultured rabbit blastocysts through identification of the sex chromatin (Braude, Pickering, Flinter, & Ogilvie, 2002). Then, in the 1980s, the invention of PCR (Braude, Pickering, Flinter, & Ogilvie, 2002) allowed for the improved testing of amplified DNA sequences. The first clinical application was in 1990, in which female genotyped embryos were transferred for couples at risk of transmitting x-linked disorders (Braude, Pickering, Flinter, & Ogilvie, 2002).
PGD distinguishes itself from other assisted reproductive technology in that it involves testing prior to implantation, as its name implies. Implantation refers to the event in which an embryo comes into contact with the uterus; this occurs approximately one week after fertilization a zygote is formed with half of both parents’ DNA (Niakan, Han, Pedersen, Simon, & Pera, 2012). The formation of the zygote is considered the beginning point of the embryo (Niakan, Han, Pedersen, Simon, & Pera, 2012). In the time taken to migrate down the fallopian tubes to the uterus, the zygote develops into a blastocyst. It is at this developmental stage when embryos are typically tested for single gene and chromosomal...

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...s typically offered to parents at risk of transmitting DMD in the context of either preventing an affected boy who will suffer early onset of the disorder and most likely an early death (Altarescu, et al., 2014), whereas the prevention of a a girl who is a carrier may or may not be considered acceptable (REF?). This use of PGD in this case is more open to debate than HD because an embryo identified as a carrier will most likely be healthy, and its destruction can be considered unethical. On the other hand, the prevention of the future burden of transmission for one’s children can be considered ethical by others. Another factor worth considering is that distinguishing between a female carrier and non-carrier is not as accurate as distinguishing between a male with and without the affected gene (REF?). For the above reasons, the decision to undergo PGD is complicated.

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