A baby boy born to a Jordanian couple is the first to be born using a “three-parent” technique – DNA from three separate individuals.
The controversial process, which is only legal in the United Kingdom, allows parents with rare genetic abnormalities to have healthy offspring. The Jordanian couple had been trying to start a family for the past 20 years, but the mother carries genes for Leigh syndrome, a fatal condition that affects the nervous system. The mother was able to give birth to a baby girl in 2005, but she died at six years old due to the genetic mutation that was passed on to her. The couple’s second child inherited the same syndrome and lived for only eight months.
Genes for Leigh syndrome lie in mitochondrial DNA, which carry 37 genes passed from the mother. Mitochondria are separate from the rest of the DNA that dictates things like physical traits, as these reside in the cell’s nucleus. The mother was healthy, but her genetic anomalies would keep passing on to any children she might have, New Scientist reports.
The couple decided to seek for options that would allow them to have a healthy child and found Dr. John Zhang and a team at the New Hope Fertility Center in New York City. Zhang has been working on a new method to address mitochondrial mutations using the “three-parent” technique. There are a few ways to do this.
In the UK, the legal method is called pronuclear transfer, wherein a mother’s egg and a donor’s egg are fertilized by a father’s sperm. Before the eggs begin dividing into early-stage embryos, the nuclei are removed. The nucleus from the donor’s fertilized egg is replaced by the nucleus from the mother’s, essentially destroying the donor egg and transferring healthy mitochondria while keeping the mother’s DNA.
However, the couple felt strongly about the destruction of any embryos, so Zhang suggested a different approach called spindle nuclear transfer.
Zhang removed the nucleus from a donor egg, took the nucleus from the mother’s egg and moved it to the donor egg.
The egg, which now carried mitochondrial DNA from the donor and nuclear DNA from the mother, was then fertilized with the father’s sperm.
Zhang and his team created five embryos, only one of which developed normally. The embryo was implanted in the mother, and she was able to carry the child to full term. At five months, the baby boy is healthy and shows no signs of Leigh syndrome.
Since none of these methods are legal in the USA, Zhang performed the procedure in Mexico and is confident that he made the right choice. While many have taken up arms over the ethics surrounding DNA manipulation, scientists have backed Zhang, calling the procedure both exciting and revolutionary.
Sian Harding, who was part of the UK review board on pronuclear transfer, pointed out that the team seems to have taken the ethical route. They did not destroy embryos and used a male embryo so that the child would not be able to pass on any mitochondrial DNA. When Zhang and his team tested the baby’s mitochondria, they found less than 1% carried the mutation, which they expect is too low to cause any damage. It takes around 18% of mitochondrial abnormalities to trigger health conditions.
Aside from ethics, critics say that safety is a concern. The last time scientists attempted to create a baby using three DNA contributions in the 1990s. They injected mitochondrial DNA from a donor into a woman’s egg. Two of the fetuses developed genetic disorders, causing the US Food and Drug Administration to ban the practice. The problem could have been that the embryos had mitochondria from two sources.
The baby will continue to be monitored for any symptoms. The research summary of the procedure was published in the journal Fertility & Sterility.