A recent study has described why human embryos may exhibit such high levels of aneuploidy resulting in early pregnancy loss.
Mutations in eggs that attempt to destroy the partner chromosome at fertilisation but fail, can lead to embryos developing with the incorrect number of chromosomes (aneuploidy). Aneuploidies have been detected in all mammal species studied, though not in amphibians and fish (which do not carry their young). Humans exhibit very high rates of aneuploidy, despite being evolutionarily quite advanced.
Professor Laurence Hurst from the Milner Centre for Evolution which carried out the study, proposes that ‘selfish’ mutations which destroy embryos, may have an advantage in mice (which birth multiple offspring), as aneuploid embryos perishing earlier may enable siblings to benefit from a greater share of resources in the womb. In humans, the early loss of pregnancy of an aneuploid embryo, would avoid expending energy on the abnormal pregnancy over the full term and provide the opportunity for the mother to reproduce again in the hope of a successful pregnancy.
Professor Hurst has identified a protein ‘BUB1’ which may be implicated in aneuploidy. As maternal age increases, the levels of BUB1 decrease and aneuploid eggs become more plentiful. The identification of these proteins may enable further research into helping women who suffer from infertility or pregnancy loss.