Britain is a step closer to allowing DNA swaps that, when combined with in vitro fertilization, may spare children from inherited mitochondrial diseases.
The techniques – which involve transferring chromosomes from an egg containing faulty mitochondria to one without mutations – could be allowed in humans if additional cell and animal experiments continue to show that the techniques are safe, concludes a scientific report submitted to the UK’s Human Fertilisation and Embryology Authority (HFEA). It is currently illegal in the UK to alter the DNA in a human embryo for treatment.
“From all the available evidence, we could find nothing to say they’re unsafe,” said Robin Lovell-Badge, chair of the committee that put together the report and a developmental biologist at London’s National Institute of Medical Research, at a press briefing today.
His committee did not call on the government to legalise these techniques, which produce a child with nuclear DNA from his or her mother and mitochondria from another woman. Nor did the committee consider ethical and legal implications of these transfers, which are likely to be taken up by the UK government before it makes any policy decisions.
As many as 1 in 250 people carry a potentially disease-causing mitochondrial mutation. Mutations in mitochondrial DNA, passed from a mother to her offspring, are linked to a number of conditions, including type 2 diabetes, mitochondrial myopathies, and Leigh syndrome, a neuromuscular disease that typically strikes infants.
The HFEA report focuses on two approaches. Maternal spindle transfer (MST) involves transferring the chromosomes of an unfertilized egg into another woman’s egg, stripped of its nucleus. That hybrid cell is then fertilized in vitro. In 2009, scientists in Oregon reported that rhesus macaques conceived this way are born healthy and develop normally.
However, the report recommended that the technique be tested in human embryos before MST get green lighted. Shoukhrat Mitalipov, a reproductive biologist at the Oregon Health and Science University in Portland who led the monkey work, says experiments with human cells are underway in his lab.
In pronuclear transfer, the second technique examined in the HFEA report, scientists shuttle the nucleus of a fertilized egg into another fertilized egg, lacking mitochondrial mutations and removed of its nucleus. Last year, a British team applied this approach to fertilized human eggs that were not suitable for implant and found that the resulting embryos developed normally to the 100-cell blastomere stage.
The HFEA report called for additional research applying the same technique to normal fertilized human eggs to improve efficiency, as well as tests in monkeys similar to those Mitalipov’s team performed.
In a letter to the health minister released today, several groups including the Medical Research Council and the Wellcome Trust called on the government “to publish a timetable for the introduction of regulations so that once sufficient pre-clinical evidence is established, clinical treatment is not unduly delayed.”
If Britain does legalize the nuclear transfer techniques, it would be the first nation to do so. However, the Australian government is considering a similar proposal, according to the Sydney Morning Herald.
“I think it’s about time,” says Mitalipov, who hopes to one day secure approval to try these approaches on patients in the United States. “HFEA is a pioneer and I really applaud their courage.”
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