Three-parent baby technique works successfully

By Tara Shaw

The first baby to be conceived using a “three-parent” technique was born earlier in the year, it has been revealed by New Scientist magazine. The boy, who is now five months old, was born to a Jordanian couple using a special form of in vitro fertilisation (IVF) which combines the DNA of three different people. The technique is called maternal spindle transfer and involves using mitochondrial DNA from a donor, which in this case was an anonymous female.

Most of your DNA is contained in the nucleus of each cell, but a very small amount is contained separately in the mitochondria, the small compartments which generate the cell’s energy. Mitochondrial DNA, or mtDNA, is passed onto a child directly from its mother. This means that if the mother is a carrier of any genetic mutation or disease in her mitochondria, it is highly likely that the baby will develop the disease or become a carrier too.

The couple, who have not been named, were treated by a New York-based fertility team after their first two children died as a result of Leigh syndrome, a rare neurological disorder which is inherited through the mtDNA. Infants with the syndrome typically have low muscle strength and a lack of control over movement, and their symptoms usually lead to death within several years. Although she is healthy, the mother carries the mutation for Leigh syndrome in around a quarter of her mtDNA, and had already experienced four miscarriages by the time the couple’s first child was born.

The technique was performed by taking the nucleus, containing the majority of the mother’s DNA, from the mother’s egg cell and discarding the rest of the cell which contained the unhealthy mitochondria. The nucleus of an egg from the donor was then removed, leaving an egg containing only healthy mtDNA. The nucleus from the mother was inserted into the donor’s egg, and the egg then fertilised with the father’s sperm. This generated a healthy embryo which could then be implanted into the mother’s womb.

The team, led by Dr. John Zhang, travelled to Mexico to perform the treatment, as maternal spindle transfer has not been approved in the United States. Another, similar technique has been developed and was made legal in the UK in February 2015. However, this method involves the destruction of an embryo, which the couple were opposed to.

The idea of replacing mtDNA in this way is controversial, with some people arguing that it starts us on a slippery slope that could eventually lead to “designer babies”. It has also been suggested that the technique is unnecessary and that research efforts should be directed at helping those who have already been born with mitochondrial diseases. In the meantime, however, the baby is showing no signs of disease and Dr Zhang’s team hope the technique will give parents with rare genetic mutations the hope of having healthy children.

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