Doctors will seek permission this month to create Britain’s first baby from the DNA of three people if the government’s fertility regulator approves the treatment for carefully chosen patients.

Specialists in Newcastle are ready to offer mitochondrial replacement therapy (MRT) to women who are in danger of passing on devastating and often fatal genetic disorders to their children. The conditions affect about one in 10,000 births.



What is mitochondrial replacement therapy (MRT)? MRT is an experimental treatment that was made legal in Britain in 2015. It aims to prevent serious disorders from being passed to children, caused by mutations in mitochondria, tiny structures that provide energy inside cells. Children inherit all their mitochondria from their mothers. MRT uses healthy donor mitochondria to replace the faulty ones. The child therefore has the usual 46 chromosomes from its parents, plus additional DNA from the donor's mitochondria. To perform MRT doctors pluck the nucleus from the mother’s egg, place it in a healthy donor egg, then fertilise it. Another similar approach uses fertilised eggs.

A scientific review commissioned by the Human Fertilisation and Embryology Authority (HFEA) concluded on Wednesday that the therapy should be approved for “cautious clinical use” when children are at risk of inheriting specific genetic diseases.



The HFEA will now consider the findings and invite clinics to apply for licences if it endorses the recommendations at a meeting on 15 December. Last year, parliament changed the law to allow MRT, but scientists continued with further experiments to assess the treatment’s safety.



The Newcastle team has already selected patients who may be suitable for the therapy and plans to submit a licence application as soon as the HFEA gives the go-ahead.



“Once we get the green light from the HFEA, we are ready to submit an application for a licence to offer mitochondrial donation treatments here at Newcastle Fertility Centre,” said Mary Herbert, professor of reproductive biology at Newcastle. “This will form part of a comprehensive programme of NHS-funded treatment for families affected by mitochondrial DNA disease.

“My own belief is that it should be an option that is offered to these patients as one of their reproductive choices,” said Doug Turnbull, a neurology professor who has pioneered the treatment at Newcastle University. “We can’t say that it abolishes the risk of transmitting mitochondrial disease, but it is a strategy to reduce the risk.”



MRT was developed to help women with harmful genetic mutations in their mitochondria, the tiny battery-like structures that provide energy inside cells. Mitochondria are passed on from mother to child, and when they are faulty, the children can suffer progressive diseases that affect the most energy-demanding tissues in the body, such as the brain, heart, muscles and liver.

MRT aims to overcome the problem by replacing the mother’s defective mitochondria with those from a healthy donor. The resulting baby would have the usual 23 pairs of chromosomes from both parents, but with mitochondria from the healthy donor.

Women with faulty mitochondria can already side-step the risk of passing on disease by adopting or having IVF with healthy donor eggs. To have genetically-related children, they can either take the risk with natural birth, or have a procedure called preimplantation genetic diagnosis (PGD) which can screen out IVF embryos with highly-mutated DNA. While effective for many women, PGD tends to reduce the risk rather than rule it out, and cannot help when all of a woman’s embryos have highly-mutated mitochondria.



MRT could be an effective alternative, but the treatment has its own risks. Recent studies in the US and UK have found that small amounts of mutated DNA that remain in MRT embryos may bounce back as the embryos grow. The process is called reversion and raises the potential that children born from MRT could still develop mitochondrial diseases.



In a new report published in Nature, Shoukhrat Mitalipov at the Oregon Health & Science University, used MRT to create healthy embryos from the eggs of women with the rare mitochondrial conditions Melas and Leigh syndrome. While the experiments were a success, the scientists found that in about 15% of cases, the mother’s defective mitochondria bounced back in some of her embryo’s cells. It is unclear why this happens, but one theory is that some mitochondria replicate faster than others, allowing them to dominate the healthy donor mitochondria.



“The procedure removes 99% of the mutant mitochondria, so only about 1% remains. But that 1% may sometimes come back like a cancer,” Mitalipov said.

“The danger is that in some cases, the mutant mitochondria will come back and the children may still have the disease that was originally removed from the embryo.”



When the US team looked deeper into the problem, they found genetic signatures that helped predict whether the faulty mitochondria would bounce back or not. That could help doctors find the best donors for MRT, but the tests need more work. “When we have a patient, we should be able to screen multiple egg donors and chose one that will be least likely to have this problem,” Mitalipov said.



The HFEA’s scientific review recommends that any clinics that receive MRT licences should offer tests to pregnant women to check whether their babies are genetically healthy. If the HFEA endorses the review, it could issue the licences in a few months, allowing doctors to treat the first patients as early as the spring.

Any MRT babies that are born in the UK will not be the first in the world. Earlier this year, a US team reported the birth of a baby boy after doctors performed the treatment at a clinic in Mexico. The child appears to be healthy, but scientists are keen to follow the boy’s development.

Sally Cheshire, chair of the HFEA, said the scientists’ review would be key to discussions about when was the right time to allow MRT in British clinics. “It is now down to us as an authority to consider these recommendations and decide if the treatments can be offered,” she said.