Mitochondrial DNA replacement therapy successfully tested in human eggs

Scientists have successfully created human embryos containing donated mitochondrial DNA in an effort to stop children inheriting life-threatening diseases. The technique, known as spindle transfer, involves transferring the nucleus from the egg of a woman with potentially disease-causing mutations in her mitochondrial DNA, into a healthy donor egg which has had its nucleus removed.

'Using this process, we have shown that mutated DNA from the mitochondria can be replaced with healthy copies in human cells', said Dr Shoukhrat Mitalipov from Oregon Health and Science University in Portland, who led the research. 'This research shows that this gene therapy method may well be a viable alternative to preventing devastating diseases passed from mother to infant'.

Mutations in mitochondrial DNA, affecting approximately one in 200 babies, can lead to a range of problems including; muscle weakness, heart disease, learning disabilities and blindness. Spindle transfer was devised with the aim of allowing mothers to prevent the transmission of such mitochondrial disorders to their children and future generations, by replacing the mutant mitochondrial DNA with that from a healthy donor egg.

The researchers decided to test the technique on human cells after demonstrating that it can produce healthy offspring in monkeys. They showed that the process resulted in normal human embryos and moreover can be performed using frozen eggs. This is crucial if the method is to become a practical reality in the clinic. The next step - human clinical trials - is now under serious discussion. 'I would say that it's safe enough at this stage to proceed to clinical trials', said Dr Mitalipov.

The technique is not currently permitted for clinical use in the UK, as it falls within the status of germline gene therapy. This refers to any alterations to the DNA of sperm or eggs that are subsequently passed down to future generations.

The UK's Human Fertilisation and Embryology Authority (HFEA) are now overseeing a public consultation on whether this and other similar techniques, such as that carried out by UK researchers at Newcastle University (BioNews 554), should be made available to prevent the inheritance of mitochondrial diseases (Bionews 673).

Further research is needed into the viability of these techniques, as in the current study only half of the human eggs that underwent spindle transfer were successfully fertilised to produce embryos. Professor Peter Braude, a member of the HFEA expert committee, told the Independent that the research 'is exactly the sort of science that the HFEA committee recommended needed doing, and demonstrates further the feasibility of this technique. However it is still a long way off ready for human use'.

The study was published in the journal Nature.