In what experts are calling a “revolutionary” medical event, the first baby containing the DNA from three different people was born five months ago after being conceived through a new and controversial technique. The divide is due to the method of conception: a three-parent technique called “spindle nuclear transfer,” the details of which were published last week in the journal Fertility and Sterility.
The controversial three-parent in-vitro fertilization (IVF) procedure is meant only for people who carry genes for fatal and rare diseases, and who do not want to pass the mutation down to their baby. Although the technique has only been legally approved in the UK, a team of doctors from New York performed the procedure in Mexico where there are no laws prohibiting it — unlike in the U.S., where the technique it is still up for consideration.
The boy’s mother carries genes for Leigh syndrome, a fatal disorder that affects the developing nervous system. While she is healthy, Leigh syndrome was responsible for the deaths of her first two children.
The couple sought help from Dr. John Zhang, a reproductive endocrinologist at New Hope Fertility Center in New York City.
Some diseases — including Leigh syndrome — are passed through the DNA of the mitochondria, the part of the cell responsible for generating energy. These genes only get passed down from the mother.
Dr.Zhang opted to try a three-parent IVF technique to ensure the mother’s mitochondrial disease mutation would not be passed along to the baby. In theory, there are a few ways of doing the three-parent technique, but in this particular case, Dr. Zhang used an approach called “spindle nuclear transfer.”
The idea behind the technique is to substitute the faulty mitochondrial DNA in a mother’s egg with a third set of DNA from a donor’s egg in an attempt to avoid these inherited conditions. Hence, “three parents”: the father (sperm), mother (egg, with faulty mitochondrial DNA removed), female donor (mitochondrial DNA).
During the procedure, Dr. Zhang removed the healthy nucleus from one of the mother’s eggs and inserted it into a donor’s egg which had its own nucleus removed. The resulting egg – with nuclear DNA from the mother and mitochondrial DNA from a donor – was then fertilized with the father’s sperm.
This approach resulted in the creation of five embryos that contained genetic material from three parents – the mother, the egg donor, and the father. However, only one embryo developed normally, which was later implanted into the mother womb via normal IVF. The child was born nine months later in April, 2016.
The team of doctors told New Scientist that the baby has not shown any signs of developing the illness. His mitochondria have been tested and less than 1% of the baby boy’s mitochondria carry the faulty DNA mutation, which is believed to be too low a level to lead to disease.
Although the technique is illegal in the U.S., Dr. Zhang believes this baby’s birth will encourage progress around the world for similar cases. And despite its controversy, he is adamant that he made the right choice. “To save lives is the ethical thing to do,” he says.
Sian Harding, a medical professor and bioethics adviser who reviewed the ethics of the technique in the U.K., told New Scientist the case seems to have been handled according to ethical standards. The team avoided destroying embryos, and used a male embryo, so that the resulting child wouldn’t pass on any inherited mitochondrial DNA. “It’s as good as or better than what we’ll do in the UK,” says Harding.
Dr. Zhang and colleagues are expected to describe the case at the American Society for Reproductive Medicine’s annual meeting in Salt Lake City in October.