01 September 2009
ByAppeared in BioNews 523
A variation of SCNT (somatic cell nuclear transfer), reported online in the journal Nature, could be used in humans to allow women with a certain group of incurable inherited conditions - known as mitochondrial disorders - to have children without passing on the condition. Because the technique, developed by Dr Shoukhrat Mitalipov and team from the Orgeon National Primate Research Centre, US, involves the sperm from one monkey and two eggs from different monkeys it has been dubbed by the press as the creation of 'three-parent' embryos.
The technique involves transferring the nucleus of an unfertilised egg from one monkey to an egg from another monkey that has had its nucleus removed. Tiny structures present in the egg called mitochondria, contain a small amount of genetic material known as mitochondrial DNA (mtDNA) and are passed on only through the mother. The resulting egg would therefore have mitochondria from one female monkey, containing a very small amount of mtDNA, but its remaining 25,000 or so genes would come from the male and female monkeys who contributed the sperm and egg nucleus to the fertilised egg. If the technique could be replicated in humans, an affected mother could therefore have a child without passing on her faulty mitochondrial genes.
One in 6,500 births in the UK are affected by defects in mtDNA, causing some 50 known genetic disorders, including muscular dystrophy and fatal liver failure. Whilst embryos prepared for IVF can be screened for genetic abnormalities through PGD, it is poorly-understood how mtDNA mutations exert their effects on the body.
'The only way to treat these defects is to replace the genes', said Dr Mitalipov. 'This is gene transfer involving the germline, which is a concern, but we are pursuing it not for general use but for patients with mutations they will pass to the next generation. We believe this technology will prevent that.'
15 embryos were created and implanted into nine surrogate female monkeys, of which three became pregnant. Four monkeys have since been born. Very little of the donor monkey's mtDNA was detected in offspring, suggesting the technique had been a success.
The new Human Fertilisation and Embryology Act, which comes into force on 1 October, recognises what it calls the ‘devastating effects' of mitochondrial diseases and will allow for secondary legislation to sanction treatment of mitochondrial diseases should therapies be developed.
Professor Sir Ian Wilmut, of the medical research centre for regenerative diseases in Edinburgh, who created Dolly the sheep, commended the work: 'The authors are to be congratulated for being the first to demonstrate in primates a new route to therapy. This brings us an important step nearer to being able to prevent the birth of children with a particular type of inherited disease.'
British scientists at the University of Newcastle provoked controversy last year after claiming to have created ten human embryos using similar methods. The embryos were destroyed within 14 days of their creation, in accordance with UK law.