A five-month-old boy is the first ever baby to be born using a new technique that incorporates DNA from three people.
The controversial technique enables parents with rare genetic conditions to have healthy babies.To date, the practice has only been legally approved in the UK. But embryologists hope that the successful birth of the child to Jordanian parents who were treated by a US-based team in Mexico, will encourage progress around the world.
The mother of the child carries genes for Leigh syndrome, a fatal disorder that affects the developing nervous system. Mitochondrial DNA is housed in cells that supply energy, and is inherited from genetic mothers. This is separate from the majority of human DNA, which is housed in each cell’s nucleus.
Around 25 percent of the mother's mitochondria have the disease-causing mutation. While she is healthy, Leigh syndrome caused the deaths of her first two children. The couple sought out the help of John Zhang and his team at the New Hope Fertility Center in New York City.
Zhang has been developing a way to avoid mitochondrial disease using a "three-parent" technique. This new scientific method was to replace defective mitochondrial DNA (mtDNA) that exposed the child to the risk of inheriting Leigh syndrome, a fatal disorder affecting the developing nervous system.
The traditional method approved in the UK is pronuclear transfer which consists in the fertilization of both the mother's egg and a donor egg with the father's sperm. Before the fertilizaion develops into early-stage embryos, each nucleus is removed. The donor's fertilised egg nucleus is removed and then replaced by the mother's fertilised egg.
However, the couple was not comfortable with this approach for religious reasons. As Muslims they were against the destruction of two embryos. Therefore Zhang undertook a different procedure called spindle nuclear transfer. This method consists in the removal of the nucleus from one of the mother's eggs before inserting it into an egg taken from the donor with its nucleus removed. This produces an egg with mitochondrial DNA from the donor and nuclear DNA from the mother which is then fertilised with the father's sperm.
The team opted for a more ethical approach with this technique, says Sian Harding, who reviewed the ethics of the UK procedure. The team avoided destroying embryos, and used a male embryo, so that the resulting child wouldn't pass on any inherited mitochondrial DNA.
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