The research started with monkeys. In August 2009, scientists from the Oregon National Primate Research Center published a study1 in which they transplanted the DNA of monkeys with damaged mitochondria into “chromosome-empty” eggs of monkeys with healthy mitochondria. Fifteen viable embryos resulted, four of which were brought to term. The purpose of this research was to prevent conditions such as blindness, deafness, dementia, or diabetes, all of which can be caused by faulty mitochondria and affect one in every 6,500 children.
Recently, Doug Turnbull and other researchers from Newcastle University took the primate research a step further by merging fertilized human eggs—thus creating the potential for babies with three parents.2 The researchers essentially replicated the earlier study’s method, taking the DNA, or pronuclei, from the embryo created by the mother’s egg and father’s sperm and injecting it into a “hollowed out” egg belonging to a second woman (i.e. an egg from which the pronuclei have been removed). This creates an embryo with healthy mitochondria (from the donated embryo) while preserving the parental DNA (from the pronuclei).
Ethical concerns aside, several questions remain:
- What might be the effects of having two biological mothers?
- Could the tiny amount of damaged mitochondrial DNA that ends up in the healthy host egg still be enough to cause mitochondrial disease?
Still, researchers are optimistic that their technique will be fine-tuned and ready to undergo the ethical gauntlet in as little as three years time.
Check out another 2009 study3 in which researchers attempt to improve IVF for older women by implanting their nuclei, containing the majority of the DNA for the baby, into the healthy cytoplasm of younger donor mothers’ eggs.
1 Tachibana, M., Sparman, M., Sritanaudomchai, H., Ma, H., Clepper, L., Woodward, J., Li, Y., Ramsey, C., Kolotushkina, O., & Mitalipov, S. (2009). Mitochondrial gene replacement in primate offspring and embryonic stem cells Nature, 461 (7262), 367-372 DOI: 10.1038/nature08368
2 Craven, L., Tuppen, H., Greggains, G., Harbottle, S., Murphy, J., Cree, L., Murdoch, A., Chinnery, P., Taylor, R., Lightowlers, R., Herbert, M., & Turnbull, D. (2010). Pronuclear transfer in human embryos to prevent transmission of mitochondrial DNA disease Nature DOI: 10.1038/nature08958
3 TANAKA, A. (2009). Metaphase II karyoplast transfer from human in-vitro matured oocytes to enuclueated mature oocytes Reproductive BioMedicine Online, 19 (4), 514-520 DOI: 10.1016/j.rbmo.2009.06.004