Although the mechanism by which the embryos self-corrected their abnormalities was not clear, Dr Munn believed that it probably happened when a trisomic embryo (one with three of a particular chromosome instead of the usual two) lost the third chromosome somewhere between the time that the fertilised egg first started to divide and the blastocyst stage. "However, not all the embryos were trisomic. Some had other abnormalities, namely chaotic mosaics, with all the cells abnormal but each one different from the others. These did not produce stem cells," said Dr Munn. "It is impossible to tell at this stage which embryos are capable of self-correcting and which are not."
Dr Munn's findings offer researchers an opportunity to research early embryonic development and stem cells without embryos needing to be specially created for the purpose. The embryos he used would have been discarded by couples seeking fertility treatment, after PGD showed that there were abnormalities that meant the embryos would either fail to implant, or spontaneously abort at some point in the pregnancy, or would result in the birth of a child with one of the defects that the couple were trying to avoid by having PGD in the first place.
"The use of human embryos or their purposeful creation for stem cell research has been controversial, and a ban on research using government funds has been in effect in the USA since 2001. These findings offer scientists the chance to continue their research in this important field, without having to create embryos especially for the purpose," said Dr Munn.
Contact: Mary Rice
European Society for Human Reproduction and Embryology