An American scientist, two Jordanian parents, and an anonymous donor walked into a hospital in Mexico.
That’s not the premise of a joke; those are the characters and the setting for a striking innovation in in-vitro fertilization techniques. The doctor helped the couple and their donor conceive a child in Mexico using a technique that is illegal in the US and remains heavily debated in the UK, according an exclusive report in the New Scientist.
The Jordanian parents previously had two children but they both died young from an illness called Leigh Syndrome. The disease is caused by faulty mitochondria, which are the powerhouses present in most human cells, and were passed onto the children from their mother.
When an egg and sperm combine to make an embryo, only the mother’s mitochondria are passed on to the child. Although in this case the mother herself is healthy despite having faulty mitochondria, her first two children who inherited them were not so lucky. So before trying to conceive a third time, the couple sought help from John Zhang and his team at the New Hope Fertility Center in New York, known for their work on mitochondrial diseases.
Zhang has helped pioneer a technique where healthy mitochondria from a woman donor are inserted into an embryo created by the father’s sperm and the mother’s egg. This leads to “three-parent children,” because mitochondria contain 37 out of the 20,000 genes that make up human DNA—in other words, the child will have DNA from the mother, father, and the donor.
There are three ways doctors can insert donor mitochondria into an embryo:
First is cytoplasmic transfer. This involves taking donor cytoplasm, which includes all the things in the cell except the nucleus, and adding that to a mother’s egg. The egg—now with both faulty and healthy mitochondria—is then fertilized and implanted in a womb. Some 30 or so children have been born via this method. However, in 2002, citing ethical and scientific concerns, the US Food and Drug Administration banned the technique.
Second is pronuclear transfer, in which doctors fertilize both the mother’s egg and the donor’s egg with the father’s sperm. Then, before the resulting embryos start dividing, the nucleus of both eggs is removed and the mother’s nucleus is added to the donor’s egg. This way, the embryo is born with only healthy mitochondria from the donor. This is the technique that has been approved in the UK and can be used after following licensing procedures. No births using this technique have been reported.
However, as Muslims, the Jordanian parents had religious concerns with pronuclear transfer. They weren’t comfortable destroying one embryo and saving the other. So they used a third technique called spindle nuclear transfer, where nucleus from the mother’s unfertilized egg was removed and inserted into a donor’s egg. This egg was then fertilized by the father’s sperm.
It’s illegal to use any of these therapies in the US—which is why Zhang had to go to Mexico, where, as he told the New Scientist, “there are no rules.”
Of the five embryos Zhang created using this technique, only one developed normally. The baby boy is five months old now.
Scientists are happy to hear of the baby’s birth and Zhang’s work. “It’s as good as or better than what we’ll do in the UK,” Sian Harding, a professor at Imperial College London and a member of the Nuffield Council on bioethics, who reviewed the ethics of the UK procedure, told the New Scientist.
They are also wary. About 1% of the baby’s mitochondria are still faulty, probably because they were carried over during the transfer process. That’s considerably less than the 18% that were affected in the mother’s eggs, but there’s a chance that faulty mitochondria might be better at replicating and then gradually increasing in numbers.
Despite the limitations, scientist world over will be watching the pioneering baby’s progress closely. If he remains healthy, it will give proponents more reason to call for legalizing the technique in other countries.
Update: The names of the family members were removed on Zhang’s request.