Description

Pre-implantation genetic diagnosis is used to analyse pre-implantation stage embryos or oocytes for genetic defects, generally for severe Mendelian disorders and chromosome abnormalities. New but controversial indications for pre-implantation genetic diagnosis include identifying human leukocyte antigen compatible embryos suitable as donor, sex selection and adult-onset disorders, particularly cancer. Pre-implantation genetic screening is a variant of pre-implantation genetic diagnosis to improve outcomes of in-vitro fertilization.

 Array comparative genomic hybridization is replacing fluorescence in-situ hybridization for aneuploidy screening. Besides technical advancement of array platform, the success of pre-implantation genetic screening is strongly related to the embryonic biological nature of chromosomal mosaicism. Having been applied for more than 20 years, pre-implantation genetic diagnosis is recognized as an important alternative to prenatal diagnosis. Diagnosis from a single cell, however, remains a technically challenging procedure, and the risk of misdiagnosis cannot be eliminated. Pre-implantation genetic diagnosis (PGD) is the detection of a genetic condition in an embryo prior to its implantation. A single cell is taken from a pre-implantation embryo and subjected to genetic diagnostic techniques, and only those embryos found to be free of the condition are selected for return to the uterus. This avoids the initiation of an affected pregnancy but requires couples who carry a serious genetic disorder but who may not be infertile to undergo assisted reproduction techniques. Pregnancy rates following PGD are lower than for a regular in vitro fertilizations (IVF) cycle and the congenital malformation rate is comparable to that with intracytoplasmic sperm injection (ICSI). This article describes these aspects of the PGD technique, as well as considering future developments. Reliable and accurate pre-implantation genetic diagnosis (PGD) of patient's embryos by next-generation sequencing (NGS) is dependent on efficient whole genome amplification (WGA) of a representative biopsy sample. However, the performance of the current state of the art WGA methods has not been evaluated for sequencing. Using low template DNA (15 pg) and single cells, we showed that the two PCR-based WGA systems SurePlex and MALBAC are superior to the REPLI-g WGA multiple displacement amplification (MDA) system in terms of consistent and reproducible genome coverage and sequence bias across the 24 chromosomes, allowing better normalization of test to reference sequencing data.

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With Regards
Fathima

Journal Coordinator
Journal of Reproductive Endocrinology & Infertility