The technique is controversial because mitochondria carry their own genetic material
More research is needed into a controversial fertility treatment, known as three-parent IVF, before it can be considered safe for clinical use, a review has concluded.
Mitochondrial transfer aims to replace a faulty part of a mother's egg with healthy material from a donor.
This means a baby would have a small amount of the donor's genetic material, and therefore three biological parents.
The Human Fertilisation and Embryology Authority (HFEA) carried out the study.
The HFEA is the UK's independent fertility treatment regulator and its conclusions are published in a scientific review of the technique commissioned by the Department for Health.
Inherited disorders
The proposed treatment is designed to help families with rare inherited disorders.
These disorders are due to faulty energy-generating components of cells called mitochondria. Mothers carrying these faulty mitochondria in their eggs are at risk of having children with the inherited disorder.
Under the transfer treatment, the idea is to replace the faulty mitochondria in the eggs or fertilised embryos with those from eggs or early embryos from a healthy, unaffected donor.
The hope is these methods will enable couples to have healthy children and eliminate the disease for subsequent generations, but the technique is controversial because mitochondria carry their own genetic material (DNA).
Although this is very small and only carries a few genes, the resulting child will have this genetic material from the donor, in addition to the majority of maternally- and paternally-inherited genes present, in the nucleus of the cell.
The scientific review has concluded the two main ways of carrying out mitochondrial transplants appear safe, but a little more research is needed before it can be tried out on people.
Legislation call
Medical charities and research organisations are to press the government to prepare the legislation that would make this procedure legal so the technique can be used in the clinic as soon as it gets the go-ahead from the research community.
Dr Evan Harris, who campaigns for medical research, said: "Without regulations making clinical work legal, it will be difficult to ensure the laboratory research is funded and done in this country and that trials on affected families can be planned.
"Until the government makes clinical research and eventual treatment legal, subject to strict regulation on safety, this country risks losing its world-leading status."
Dr Harris argued for the legalisation of mitochondrial transplantation during the passage of the 2008 Human Fertilisation and Embryology Act when he was science spokesman for the Liberal Democrats.
He has now called on the government to provide a timetable for consultation and the publication of the regulations.
The report, called scientific review of the safety and efficacy of methods to avoid mitochondrial disease through assisted conception, examines three approaches to treating mitochondrial disorders.
The first, which is permitted under current regulations, is known as pre-implantation genetic diagnosis, or PGD.
This involves testing very early stage embryos from the affected couple and implanting only those that seem unaffected by the genetic disorder.
The report authors concluded the technique was unreliable for some disorders and could not guarantee the resulting child would be healthy.
Pro-life groups
The two other techniques are not permitted and would require a change in legislation for its use in the clinic.
Research on human embryonic material however is permitted, provided it is not implanted into a woman's womb.
One technique, known as maternal spindle transfer, involves transplanting the nuclear genetic material (in the form of chromosomes) from an unfertilised egg carrying the abnormal mitochondria obtained from the "patient" (the mother) into an empty donor egg, which is then fertilised.
The other, known as pro-nuclear transfer, involves transplanting the genetic material from a fertilised egg from the patient into a healthy "empty" fertilised egg from a donor, which has had its nuclear genetic material removed.
Some pro-life groups object more to this technique as it involves the creation and destruction of embryos.
Experiments with monkeys and work with embryonic material show promise.
But the HFEA's scientific review says more work needs to be carried out to show that embryos produced by either technique will develop normally.
The report authors also want research that compares the effectiveness of each technique before clinical trials are given the go-ahead.
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