What This Means
Breaking down key terms
In an analysis from July 2011 to April 2015, chromosome abnormalities have been found in about 60,000 blastocysts tested through array comparative genomic hybridization (aCGH). First of all, a chromosome abnormality is when there is a missing, extra, or irregular portion of chromosomal DNA. This occurs as an accident in the egg or sperm and when this occurs, abnormalities are present in every cell of the body. A blastocyst refers to the human embryo 5 days after fertilization. Finally, aCGH is the latest testing technique used to identify chromosomal abnormalities. It permits testing of all chromosomes of an embryo, obtained from a single cell biopsy. Now that we have all the terms broken down, let’s get started on the research.
In this article you’ll learn:
- What the research entails
- About the different abnormalities being assessed
- Where the increase in abnormality comes from and the complexity of them
Objectives & Materials
What did the researchers assess?
Researchers from Reprogenetics, a Cooper Surgical Company in New Jersey, set out to assess the results of blastocysts via aCGH by age and type of abnormality. 60,492 blastocyst biopsies were analyzed over the course of about 3 years from 12,275 cycles of preimplantation genetic screening (PGS) using blastocyst biopsy and aCGH. Following the Society for Assisted Reproductive Technology (SART) age groups, they were categorized to examine the percentage of embryos that were euploid, monosomic, trisomic, had chromosome gains or losses, or double aneuploidies.
Results & Conclusion
What are the outcomes of the assessment of blastocysts
As I’m sure anyone can guess, chromosome abnormalities increased with advanced maternal age from 31% in egg donors to 85% in women older than 42. Not only that, the complications of the abnormalities also increased with advanced maternal age. There are double and multiple abnormalities increasing and single full aneuploidies and single partial aneuploidies decreasing. A partial aneuploidies is the presence or absence of a fragment of a chromosome. The proportion of full monosomies to trisomies were 50:50 ratio of monosomies to trisomies, but for partial abnormalities it was skewed 69:31 towards chromosome losses. However, the total rate of partial abnormalities does not change with advancing age. In other words, these different tendencies, according to the analysis, indicate different origins of partial and full aneuploidies. For instance, full aneuploidies is mostly meiotic in origin. Meiosis is the process where chromosomes are copied, paired up and separated create eggs or sperm. On the other hand, partials remain mitotic (non-age related) or paternal in origin with the resulting chromosome fragments being lost more easily than gained.