Chromosomal problems affect nearly all hum...( Amsterdam The Netherlands: For the f...)

Amsterdam, The Netherlands: For the first time, scientists have shown that chromosomal abnormalities are present in more than 90% of IVF embryos, even those produced by young, fertile couples. Ms Evelyne Vanneste, a PhD student in the Centre for Human Genetics and the University Fertility Center, Leuven University, Belgium, told the 25th annual conference of the European Society of Human Reproduction and Embryology today (Wednesday July 1), that the surprising finding meant that current techniques used in preimplantation genetic screening (PGS), where embryos are screened genetically in order to select the best embryo for transfer, do nothing to improve pregnancy and live birth rates. Indeed, it can lead to potentially viable embryos being discarded, she said.

Ms Vanneste and her team studied each cell from 23 three or four day-old IVF embryos from young (less than 35 years old), fertile couples who had asked for preimplantation genetic diagnosis (PGD). PGD is carried out where one or both parents have a known genetic abnormality, in this case an X-linked disorder or the microdeletions (loss of a tiny piece of a chromosome) that can cause such disorders as the cancer predisposition syndrome neurofibromatosis type 1. The embryos are screened to avoid the implantation of one carrying that abnormality. Such embryos are the most representative of normal human embryogenesis, the process that begins once an egg has been fertilised.

Using new technologies that can detect chromosomal aberrations in the whole genome (all human chromosomes) of a single cell, the team was able to screen embryonic cells at a much higher resolution than previously, and hence identify more chromosomal abnormalities than has been possible using the current technique, fluorescent in situ hybridisation (FISH), which can only analyse ten of the approximately 32,000 genetic regions at the same time.

"Until now, the majority of studies analysing the genetic compositi
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