Researchers have made a significant breakthrough in reproductive science, claiming to have successfully “rejuvenated” human eggs. This advancement could dramatically enhance the success rates of in vitro fertilization (IVF) for older women. The study indicates that a specific age-related defect causing genetic errors in embryos may be reversed by introducing a vital protein into the eggs.
In experiments, eggs donated by fertility patients received microinjections of a protein called Shugoshin 1. The results showed that these treated eggs were nearly half as likely to exhibit genetic defects compared to untreated eggs. If further trials confirm these findings, this approach could significantly improve egg quality, which is a leading cause of IVF failure and miscarriage among older women.
Prof Melina Schuh, a director at the Max Planck Institute for Multidisciplinary Sciences in Göttingen and co-founder of Ovo Labs, emphasized the importance of this research. “Overall we can nearly halve the number of eggs with [abnormal] chromosomes. That’s a very prominent improvement,” she stated. Many women in their early 40s may have eggs available, but almost all of these eggs possess incorrect chromosome numbers, which is a major barrier to successful conception.
The findings will be presented at the British Fertility Conference in Edinburgh on March 15, 2024, and have already been published as a preprint on the Biorxiv website. The decline in egg quality is a primary contributor to the steep drop in IVF success rates as women age. For instance, the average birth rate for each embryo transferred in IVF treatment is approximately 35% for women under 35, but plummets to just 5% for those aged 43 to 44, according to the most recent UK statistics.
Dr Agata Zielinska, co-founder and co-CEO of Ovo Labs, shared insights on the implications of this research. “Currently, when it comes to female factor infertility, the only solution available to most patients is multiple IVF attempts to improve the likelihood of success. What we envision is that many more women would be able to conceive within a single IVF cycle,” she noted.
The new technique specifically targets a vulnerability in eggs related to a cellular process known as meiosis. During meiosis, sex cells—either eggs or sperm—reduce their genetic material by half to form embryos. In eggs, this process requires 23 pairs of X-shaped chromosomes to align correctly. During fertilization, these pairs ideally split down the centre, resulting in a cell with exactly 23 chromosomes from the mother and the rest supplied by the sperm.
Older eggs often experience a loosening of chromosome pairs at their midpoint, leading to improper alignment and chaotic movement within the cell. This disruption can result in embryos with incorrect chromosome numbers, increasing the risk of genetic disorders.
In previous studies, Schuh and her team identified that the protein Shugoshin 1, which serves to stabilize chromosome pairs, diminishes with age. The current experiments involving mouse and human eggs demonstrated that microinjections of this protein could potentially counteract the premature separation of chromosome pairs. At the Bourn Hall fertility clinic in Cambridge, researchers observed a reduction in the defect rate from 53% in untreated eggs to 29% in those treated with Shugoshin 1. Among eggs from women aged over 35, the defect rate fell from 65% to 44%, though this result was not statistically significant due to a limited sample size.
“What is really beautiful is that we identified a single protein that, with age, goes down, returned it to young levels and it has a big effect,” said Schuh, highlighting the potential impact of their findings.
While this innovative approach will not extend fertility beyond menopause, it does represent a promising direction for IVF treatments. Currently, aside from intra-cytoplasmic sperm injection (ICSI), few methods involve microinjections into eggs. The research team is in discussions with regulatory bodies regarding clinical trials and expects no significant safety issues.
An essential aspect of future research will be to determine if the improved egg quality leads to embryos with fewer genetic errors. Dr Güneş Taylor from the University of Edinburgh, who was not involved in this research, described the findings as “really promising.” She noted the importance of developing effective solutions for older eggs, stating, “If there’s a one-shot injection that substantially increases the number of eggs with properly organized chromosomes, that gives you a better starting point.”
The ongoing exploration in this field of reproductive science holds the potential to change the landscape of fertility treatments, offering hope to many women seeking to conceive later in life.
