Chromosome cohesion decreases in human eggs with advanced maternal age.

Aneuploidy in human eggs increases with maternal age and can result in infertility, miscarriages, and birth defects. The molecular mechanisms leading to aneuploidy, however, are largely unknown especially in the human where eggs are exceedingly rare and precious. We obtained human eggs from subjects ranging from 16.4 to 49.7 years old following in vitro maturation of oocyte-cumulus complexes isolated directly from surgically removed ovarian tissue. A subset of these eggs was used to investigate how age-associated aneuploidy occurs in the human. The inter-kinetochore distance between sister chromatids increased significantly with maternal age, indicating weakened cohesion. Moreover, we observed unpaired sister chromatids from females of advanced age. We conclude that loss of cohesion with increasing maternal age likely contributes to the well-documented increased incidence of aneuploidy.