Could this be a way to boost a flagging reserve of eggs? A technique that uses an egg’s genetic leftovers could double the number of eggs collected in IVF. The method would require another person to donate healthy eggs, but the resulting embryos would be genetically related to the initial woman.
In a typical IVF treatment, a woman takes a course of hormone-based drugs that stimulates more eggs to mature and be released than normal. A doctor then surgically removes the eggs and fertilises them in a lab. The healthiest resulting embryos are then implanted in the uterus in the hope that they will develop into a fetus.
To give the best chance of success, it helps to have lots of eggs in the first place. With drugs, most women can typically produce around 10-15. But for some – such as older women or those with a low egg reserve – the number is much smaller. This can mean they have to go through more rounds of IVF treatment to get pregnant.
Now Shoukhrat Mitalipov at Oregon Health and Science University in Portland and his colleagues have found a way to increase the number of eggs, by making use of DNA that is normally discarded as an egg matures.
Using the leftovers
Eggs are unusually big compared to most cells. In the two divisions that create an egg cell, three other cells are produced, but these are tiny. The smaller cells are known as polar bodies and eventually degrade, but they do each contain all the DNA a normal developing egg would have, prompting Mitalipov to wonder whether this could be put to good use.
His team collected eggs from 11 volunteers using the standard IVF approach, which involves collecting eggs just as the first polar body forms in the first round of cell division. Instead of discarding the polar body, the researchers placed it alongside an egg donated by another individual from which they had carefully removed the DNA-containing nucleus. The donor eggs were able to incorporate the polar body, which became something like a replacement cell nucleus.
This resulted in each woman having a set of her own eggs, plus donor eggs that carried her DNA in their nuclei. However, the donor eggs still carried a small amount of donor DNA in the mitochondria, small power-generating compartments .
Boost to supplies
All the eggs were then fertilised using sperm from a donor. “Most of the resulting embryos look very normal,” says Mitalipov, who subjected them to rounds of genetic and epigenetic testing to screen for any signs of unusual development.
Not all were healthy, though. Although the technique could in theory double the number of eggs produced in IVF, at the moment Mitalipov reckons it could increase the number by 50 per cent. “That is actually huge for IVF,” he says. “It would be a breakthrough if it made it into the clinic.”
“Around 60 per cent of IVF patients have infertility due to age,” says Mitalipov. “The number of eggs these women have declines, and there are more errors in cell division.” Such women could stand to benefit from the technique, he says.
The procedure has benefits and drawbacks, says Bert Smeets at Maastricht University in the Netherlands. “It’s nice that they are able to reuse the material [from the polar body], but on the other hand, you still need a donor egg,” he says.
He points out that the extra eggs also have donor mitochondrial DNA. This probably communicates with nuclear DNA, and we don’t know if having DNA from two different sources will be problematic, or cause any problems later in life, he says. “The simpler thing to do would be to have children younger, or freeze your eggs at a younger age,” says Smeets.
The technique would have to be approved before it can be offered in fertility clinics, but it looks safe, says Jacob Hanna at the Weizmann Institute of Science in Rehovot, Israel. “There are no red flags or scary signs,” he says. “It looks as safe as possible.”
Although three polar bodies are normally discarded in egg development, it would be technically difficult to make use of the other two, says Mitalipov. The first polar body, created during the first round of cell division, has a full set of chromosomes, whereas the others that form later only have half the number.
Journal reference: Cell Stem Cell, DOI: 10.1016/j.stem.2016.10.001
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