Egg injection boosts fertility
New mitochondria may pep up ageing eggs, without creating 'three-parent' babies.
Injecting a woman's eggs with fresh supplies of power-generating mitochondria from the egg of another woman is known to boost the success rate of in vitro fertilization (IVF). But there's a serious ethical hitch: any resulting embryos contain genetic material from three different people.
Now doctors from Taiwan report a way round the problem. Taking mitochondria from a woman's own cells and injecting them into her eggs seems to work just as well, they told a meeting of the American Society for Reproductive Medicine in Philadelphia.
Taipei Medical University, Taiwan
They injected up to 5,000 mitochondria into each egg, 5% of the total number they already contain. The researchers then fertilized the eggs in the lab, allowed them to grow into embryos and implanted them into the woman's uterus.
Of 71 attempts, 35% soon resulted in a pregnancy and 20 babies were born, revealed team leader Chii-Ruey Tzeng of Taipei Medical University on 19 October. By contrast, only 6% of attempts without mitochondrial injection had previously resulted in pregnancy in the same group of patients, none of which had reached term.
Tzeng believes that some women have difficulty conceiving owing partly to their mitochondria flagging, because eggs are thought to hang around in the ovaries from which they are formed. By contrast, cumulus cells are regularly refreshed so their mitochondria carry fewer defects.
He hopes the technique might be used to help women with a range of conception problems, or those whose eggs are simply ageing. "I think it can rescue a lot of patients," he says.
Weill Cornell Medical College, New York
Previous attempts to pep up women's eggs with fresh mitochondria have all suffered from ethical and safety concerns.
One method, called cytoplasmic transfer, involves injecting cytoplasm and mitochondria from a healthy woman's egg into the egg of an infertile woman. The US Food and Drug Authority banned this technique in 2001 (except in clinical trials), because of concerns that it raises the risk of children suffering genetic abnormalities.
There are also ethical concerns about creating an embryo containing the genetic material of three parents: the mother, the father, plus the small amount of DNA harboured in the donor woman's mitochondria.
A related experimental, and also contentious, technique involves transplanting the entire nucleus from an infertile woman's egg into the egg of a healthy woman that has been stripped of its own nucleus.
Because this technique replaces all the mitochondria in the egg, it could be used to help women whose own mitochondria carry a genetic disease that might be passed onto their children. A group in China revealed that they had tried this last year, and a British group has also applied for a licence to study embryos made by a closely related process.