Introduction to preimplantation genetic diagnosis
نویسنده
چکیده
Preimplantation genetic diagnosis (PGD) was • fi rst applied in 1988 using a polymerase chain reaction (PCR) protocol to amplify a sequence on the Y chromosome for embryo sexing for patients carrying X-linked disease. Patients have to go through in vitro • fertilization (IVF) so that their embryos may be generated in vitro. Cells are removed from oocytes or embryos and used for the genetic diagnosis. Unaff ected embryos are transferred to the patient. Th e most common biopsy procedure is • cleavage-stage biopsy, but biopsy of polar bodies and trophectoderm cells is performed clinically. Th e indications for PGD are: monogenic • disorders, chromosome abnormalities, sexing, or specifi c diagnosis of X-linked disease. PGD technology has been used to try and • improve the pregnancy rate for infertile patients by screening for aneuploidies. Indications include advanced maternal age, repeated implantation failure, and repeated miscarriages (preimplantation genetic screening; PGS). Fluorescent • in situ hybridization (FISH) is the technique used to analyze chromosomes in the biopsied cells, and is the method of choice for embryo sexing. It is also used for chromosome abnormalities and aneuploidy screening. PCR is the technique used to detect • monogenic disorders but it has been hampered by problems with contamination and allele dropout. PGD has stimulated much ethical debate. • Many countries have legislation controlling PGD and in some countries cleavage-stage and blastocyst biopsy are illegal. Social sexing is illegal in Europe and other countries. Th e fi rst 20 years has shown major advances • in the fi eld of PGD. Th e next 20 years may include the use of arrays for examining all the chromosomes, multiple genes and gene expression. PGD may be used for all IVF patients to select the genetically “best” embryo. Th e European Society for Human • Reproduction and Embryology (ESHRE) PGD Consortium has collected nine years of data on PGD and PGS. Five working groups have been set up to look at PGS, accreditation, the database, guidelines, and misdiagnosis. Additionally a pediatric follow-up and external quality assessment for FISH and PCR have been developed.
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