A five-month-old boy is the first baby to be born using a new technique that incorporates DNA from three people, New Scientist can reveal.
“This is great news and a huge deal,” says Dusko Ilic at King’s College London, who wasn’t involved in the work. “It’s revolutionary.”
The controversial technique, which allows parents with rare genetic mutations to have healthy babies, has only been legally approved in the UK.
But the birth of the child, whose Jordanian parents were treated by a
US-based team in Mexico, should fast-forward progress around the world,
say embryologists.
The boy’s mother carries genes for Leigh syndrome,
a fatal disorder that affects the developing nervous system. Genes for
the disease reside in DNA in the mitochondria, which provide energy for
our cells and carry just 37 genes that are passed down to us from our
mothers. This is separate from the majority of our DNA, which is housed
in each cell’s nucleus.
Around a
quarter of her mitochondria have the disease-causing mutation. While
she is healthy, Leigh syndrome was responsible for 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.
John Zhang holds the baby
Zhang
has been working on a way to avoid mitochondrial disease using a
so-called “three-parent” technique. In theory, there are a few ways of
doing this. The method approved in the UK is called pronuclear transfer
and involves fertilising both the mother’s egg and a donor egg with the
father’s sperm. Before the fertilised eggs start dividing into
early-stage embryos, each nucleus is removed. The nucleus from the
donor’s fertilised egg is discarded and replaced by that from the
mother’s fertilised egg.
But
this technique wasn’t appropriate for the couple – as Muslims, they were
opposed to the destruction of two embryos. So Zhang took a different
approach, called spindle nuclear transfer. He removed the nucleus from
one of the mother’s eggs and inserted it into a donor egg that had had
its own nucleus removed. The resulting egg – with nuclear DNA from the
mother and mitochondrial DNA from a donor – was then fertilised with the
father’s sperm.
Zhang’s
team used this approach to create five embryos, only one of which
developed normally. This embryo was implanted in the mother and the
child was born nine months later. “It’s exciting news,” says Bert Smeets at Maastricht University in the Netherlands.
The team will describe the findings at the American Society for Reproductive Medicine’s Scientific Congress in Salt Lake City in October.
Neither
method has been approved in the US, so Zhang went to Mexico instead,
where he says “there are no rules”. He is adamant that he made the right
choice. “To save lives is the ethical thing to do,” he says.
The team seems to have taken an ethical approach with their 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. “It’s as good as or
better than what we’ll do in the UK,” says Harding.
A
remaining concern is safety. Last time embryologists tried to create a
baby using DNA from three people was in the 1990s, when they injected
mitochondrial DNA from a donor into another woman’s egg, along with
sperm from her partner. Some of the babies went on to develop genetic
disorders, and the technique was banned. The problem may have arisen
from the babies having mitochondria from two sources.
When
Zhang and his colleagues tested the boy’s mitochondria, they found that
less than 1 per cent carry the mutation. Hopefully, this is too low to
cause any problems; generally it is thought to take around 18 per cent
of mitochondria to be affected before problems start. “It’s very good,”
says Ilic.
Smeets
agrees, but cautions that the team should monitor the child to make sure
the levels stay low. There’s a chance that faulty mitochondria could be
better at replicating, and gradually increase in number, he says. “We
need to wait for more births, and to carefully judge them,” says Smeets.
Two women, one man and a baby
A
Jordanian couple has been trying to start a family for almost 20 years.
Ten years after they married, she became pregnant, but it ended in the
first of four miscarriages.
In
2005, the couple gave birth to a baby girl. It was then that they
discovered the probable cause of their fertility problems: a genetic
mutation in the mother’s mitochondria. Their daughter was born with
Leigh syndrome, which affects the brain, muscles and nerves of
developing infants. Sadly, she died aged six.
The couple’s second child had the same disorder, and lived for 8 months.
Using a
controversial “three-parent baby” technique (see main story), the
boy was born on 6 April 2016. He is showing no signs of disease.
culled -New Scientist.com