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PGD


PRE-IMPLANTATION GENETIC DIAGNOSTIC


BY KATHY MILLER, BS, TS


Pre-implantation genetic diagnostic technologies combine advances in medical genetics with in vitro fertilization (IVF) to screen embryos for sources of reproductive failure or dysfunction caused by chromosomal abnormalities, single gene disorders, and epigenetic disorders. These technologies were originally developed as an alternative to prenatal genetic diagnosis and selective abortion for couples at high risk of having a child with a genetic disorder. In the past two decades since the first PGD babies were born1


,


embryo-screening technologies have advanced considerably. Currently there are two types of embryo screening: preimplantation genetic diagnosis (PGD) or preimplantation genetic screening (PGS).


PGD is performed when one or both genetic parents carry a gene mutation or a balanced chromosomal translocation and want to reduce the risk of transmitting these conditions to their offspring by identifying whether that specific mutation or unbalanced chromosome has been transmitted to the oocyte or embryo. PGD is available for a large number of single gene disorders including autosomal recessive disorders such as cystic fibrosis, Tay Sach’s disease,


PGS is applied when the genetic parents are known or assumed to be chromosomally normal and their embryos are screened for aneuploidy (having too few or too many chromosomes). Patients with diagnsoses of advanced maternal age, recurrent miscarriage, severe male factor or repeated IVF failures may benefit from identifying and selecting genetically normal embryos (euploidy) with the greatest implantation potential for embryo transfer.


Both PGD and PGS has been used to select embryos purely for gender preference, as an immunological match for an ill sibling, or free of gene mutations associated with adult onset diseases such as heart


spinal muscular dystrophy and sickle cell anemia; dominant diseases such as myotonic dystrophy, congenital adrenal hyperplasia, Huntington’s disease, and Charcot-Marie-tooth disease and x-linked diseases such as fragile X syndrome, hemophilia and Duchenne muscular dystrophy. In the cases of chromosomal abnormalities, PGD can be performed for reciprocal and Robertsonian translocation as well as chromosomal inversions and deletions.


THE RESOURCES LISTED IN THIS DIRECTORY ARE UNSCREENED AND SHOULD NOT BE VIEWED AS RECOMMENDATIONS OR ENDORSEMENTS, EITHER EXPRESS OR IMPLIED, BY THE AFA. 113


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