Mosaicism in human embryos
The article above outlines the development of a new, non-invasive method for obtaining embryonic DNA. The field of embryonic research and implantation is fraught with both technical and ethical difficulties and any advance which allows less invasive methodology is broadly to be welcomed. The article refers the phenomenon of mosaicism in embryos. This phenomenon has been recognised since the 1930s, and is a condition in which cells within the same person have a different genetic makeup. Research is on-going into this phenomenon. It is possible that it can affect the ability of the embryo to implant and/or develop, probably depending on the nature of the mosaicism.
Chromosome segregation errors are actually very common in human embryos following IVF. A review from University College London points out that cytogenetic studies show that approximately 60% of in vitro derived human cleavage stage embryos have at least one aneuploid cell by 3 days old. Chromosome content studies of individual cells show that 25% of these embryos have no aneuploid cells, which may relevant to the fact that 1 in 5 has the capacity to implant. Modern screening methods have allowed further insight. For example, FISH analysis was carried out on day 4, 6 and 8 cryopreserved embryos by a group in the University of Utrecht in The Netherlands. They found that 83% of 18 day 4 embryos were mosaic. The incidence had decreased to 42% on Day 8. This highlights how common this phenomenon is. Another study from Guangzhou Medical College in China used the modern preimplantation genetic diagnosis techniques of trophectoderm (TE) biopsy and DNA microarray to focus on aneuploid formation in human blastocysts from women of advanced maternal age. In this study, blastocyst aneuploidy and mosaicism were common, for example 56.6% of blastocysts were aneuploid, with errors most common in chromosome 21. However, other studies have highlighted that mosaicism is not restricted to poorly developing embryos but is also common in high quality IVF embryos. For example, a study from Vrije Universiteit Brussel in Belgium used microarray analysis to demonstrate that over 70% of excellent quality embryos were aneuploid and mosaic.
Clearly this is an example of phenomenon that needs further research to determine its significance or otherwise in development of human embryos.
Sources
LIU, J. et al., 2012. DNA microarray reveals that high proportions of human blastocysts from women of advanced maternal age are aneuploid and mosaic. Biology of reproduction, 87(6), pp. 148-148
MANTZOURATOU, A. and DELHANTY, J.D.A., 2011. Aneuploidy in the human cleavage stage embryo. Cytogenetic And Genome Research, 133(2-4), pp. 141-148
MERTZANIDOU, A. et al., 2013. Microarray analysis reveals abnormal chromosomal complements in over 70% of 14 normally developing human embryos. Human reproduction (Oxford, England), 28(1), pp. 256-264
SANTOS, M.A. et al., 2010. The fate of the mosaic embryo: chromosomal constitution and development of Day 4, 5 and 8 human embryos. Human reproduction (Oxford, England), 25(8), pp. 1916-1926
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The article above outlines the development of a new, non-invasive method for obtaining embryonic DNA. The field of embryonic research and implantation is fraught with both technical and ethical difficulties and any advance which allows less invasive methodology is broadly to be welcomed. The article refers the phenomenon of mosaicism in embryos. This phenomenon has been recognised since the 1930s, and is a condition in which cells within the same person have a different genetic makeup. Research is on-going into this phenomenon. It is possible that it can affect the ability of the embryo to implant and/or develop, probably depending on the nature of the mosaicism.
Chromosome segregation errors are actually very common in human embryos following IVF. A review from University College London points out that cytogenetic studies show that approximately 60% of in vitro derived human cleavage stage embryos have at least one aneuploid cell by 3 days old. Chromosome content studies of individual cells show that 25% of these embryos have no aneuploid cells, which may relevant to the fact that 1 in 5 has the capacity to implant. Modern screening methods have allowed further insight. For example, FISH analysis was carried out on day 4, 6 and 8 cryopreserved embryos by a group in the University of Utrecht in The Netherlands. They found that 83% of 18 day 4 embryos were mosaic. The incidence had decreased to 42% on Day 8. This highlights how common this phenomenon is. Another study from Guangzhou Medical College in China used the modern preimplantation genetic diagnosis techniques of trophectoderm (TE) biopsy and DNA microarray to focus on aneuploid formation in human blastocysts from women of advanced maternal age. In this study, blastocyst aneuploidy and mosaicism were common, for example 56.6% of blastocysts were aneuploid, with errors most common in chromosome 21. However, other studies have highlighted that mosaicism is not restricted to poorly developing embryos but is also common in high quality IVF embryos. For example, a study from Vrije Universiteit Brussel in Belgium used microarray analysis to demonstrate that over 70% of excellent quality embryos were aneuploid and mosaic.
Clearly this is an example of phenomenon that needs further research to determine its significance or otherwise in development of human embryos.
Sources
LIU, J. et al., 2012. DNA microarray reveals that high proportions of human blastocysts from women of advanced maternal age are aneuploid and mosaic. Biology of reproduction, 87(6), pp. 148-148
MANTZOURATOU, A. and DELHANTY, J.D.A., 2011. Aneuploidy in the human cleavage stage embryo. Cytogenetic And Genome Research, 133(2-4), pp. 141-148
MERTZANIDOU, A. et al., 2013. Microarray analysis reveals abnormal chromosomal complements in over 70% of 14 normally developing human embryos. Human reproduction (Oxford, England), 28(1), pp. 256-264
SANTOS, M.A. et al., 2010. The fate of the mosaic embryo: chromosomal constitution and development of Day 4, 5 and 8 human embryos. Human reproduction (Oxford, England), 25(8), pp. 1916-1926
s
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