During an October 19th news conference, John Zhang of New Hope Fertility Center in New York City announced new details regarding the outcome of a “three-parent baby” technique to conceive offspring, employed to avoid passing harmful mitochondrial DNA from a mother to her offspring. A baby born after the use of this procedure, was announced to be healthy, with only 1.6 percent of his mitochondrial DNA coming from his mother, much of whose mitochondria have a mutation that can cause Leigh syndrome, a fatal neurological disorder. The rest of the baby’s mitochondria came from a healthy donor.
In the technique, nuclear DNA is taken from the intended mother, leaving faulty mitochondria behind with the rest of the egg, and then transferred to a donor egg, from which the nucleus has been removed. The healthy egg created by the mother and the donor is then fertilizied with the father’s sperm.
Future checkups will be necessary to assess whether the mitochondria received from his mother increase over time.
The procedure, called “spindle transfer”, was performed in Mexico, 6 months ago. The technique yielded five fertilized oocytes, out which four continued developing. Only one of the five contained the right number of chromosomes, which was the one belonging to the now healthy baby boy. Oocytes are basically immature egg cells that are fertilized and eventually mature into an egg, through meiosis, a type of cell division.
According to Zhang, even though 100 percent of the mother’s mitochondrial DNA had the mutation that causes Leigh’s Syndrome, once the mother’s nucleus was transferred to the donor egg, faulty mitochondria dropped to less than 5 percent.
The technique is considered controversial, as was Zhang’s decision to hold the procedure in Mexico. According to George Daley, a stem-cell researcher at Children’s Hospital Boston, who has led several advisory groups looking into the science and ethics of these procedures, “Going to Mexico is a way to evade the stricter regulatory regime in the US and UK, the danger is to the families and the infants who are being born with this procedure. They’re taking all the risk before really being fully aware of the success rate and failure rate.”
Since mitochondria are passed to offspring only from the mother, a male child conceived using the spindle transfer method would be unable to pass to their offspring. However, there is controversy over the ethics of using the technique to implant a female embryo.
On October 13th, researchers announced that two women in Ukraine are also pregnant with fetuses created using this technique, and one of the two fetuses is female. According to Nature, a paper pending review in an unnamed journal will soon claim that a baby was conceived using spindle transfer in China. These steps forward with the method will put pressure on regulators to define clear limits and regulations for these procedures.