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May 20, 2020
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Identification of Small Segmental Aneuploidies in Preimplantation Embryos


Director of the Pittsburgh Cytogenetics Laboratory,
Associate Professor, Department of Obstetrics, Gynecology & Reproductive Sciences, Pathology and Human Genetics

Preimplantation genetic testing for aneuploidy (PGT-A) of all 24 chromosomes has become a common practice to improve implantation and clinical pregnancy rates in patients undergoing in vitro fertilization. Array comparative genomic hybridization (aCGH) and next-generation sequencing (NGS) enable identification of whole-chromosome aneuploidy and large chromosomal abnormalities. For prenatal and postnatal diagnosis, aCGH and NGS are also used to detect submicroscopic chromosomal imbalances – microdeletions and microduplications. 

In contrast to the 30 percent to 80 percent risk of sporadic whole-chromosome aneuploidy that depends on maternal age, large segmental aneuploidies are independent of maternal age but observed in 10 percent to 15 percent of embryos subjected to PGT-A. These segmental aneuploidies include de novo segmental gains and losses seen in around 10 percent of blastocysts, and genomic imbalances resulting from a known or yet undiagnosed chromosome abnormality in the parents. 

Preimplantation genetic testing for structural rearrangement (PGT-SR) is recommended to such couples, however, around 40 percent of couples with recurrent miscarriages and infertility have normal karyotype analysis despite the presence of a structural rearrangement. Moreover, de novo disease-causing submicroscopic chromosome imbalances affect around 0.3 percent of newborns and are likely more prevalent among preimplantation embryos. Current technologies are limited to identification of chromosomal imbalances larger than 5-10 Mb in size. Embryos affected by cryptic pathogenic aberration that are below the current limits of detection are routinely implanted. 

In this webinar, Svetlana Yatsenko of the Department of Pathology at the University of Pittsburgh will share how her team has used the 60K CGH GenetiSure microarray platform from Agilent to detect large aberrations (greater than 10 Mb in size), as well as aCGH with the “Single Cell Small Aberration Method” to detect copy number variants less than 10 Mb in size. 

Segmental imbalances in embryos have a significantly lower potential for implantation, leading to a diagnosis of idiopathic infertility or discovered by karyotype or microarray analysis after a miscarriage. Detection of microdeletions and duplications associated with human pathologies may improve the success rate of in vitrofertilization procedures and reduce the incidence of microdeletion syndromes.

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