Scientists to 'breed out' disease

Scientists are on the verge of ridding inherited diseases from future generations with a new technique for swapping genes between unfertilised human eggs before the resulting IVF embryos are implanted into the womb.

The technique has been successfully tested on laboratory monkeys and researchers believe it is now safe enough to apply for clinical trials on the many thousands of women at risk of giving birth to babies with some of the most debilitating inherited disorders.

Such a procedure would break new ground and raise fresh ethical concerns over the direction of IVF research because it would lead to permanent changes to the genetic makeup of children that would be passed on to subsequent generations of the same families.

This form of gene therapy, known as germline gene therapy, alters the DNA of sperm or eggs and is banned in Britain because of fears over its safety as well as the prospect of its leading to the creation of "designer babies".

But a clause in the new Human Fertilisation and Embryology Act, which comes into force on October 1, could permit a type of germline gene therapy involving mitochondrial DNA - which exists outside the chromosomes - without the need for changes to primary legislation and a parliamentary vote.

Mitochondria, the tiny "power houses" of cells and their DNA, which lies outside the nucleus, is inherited solely down the maternal line.

It is estimated that one in every 200 babies are born with mitochondrial mutations, some of which can lead to serious, life-long illnesses, such as diseases of muscles and nerves, as well as diabetes and cancer.

The study on monkeys involved "renewing" the mitochondria of their eggs by the wholesale transfer of the chromosomes of one of their eggs into the egg of a donor female that had its own chromosomes removed so only her mitochondrial DNA was left.

The aim was to test the feasibility of taking eggs from women with one of the 150 known mitochondrial DNA disorders and using them to create healthy eggs by transferring their chromosomes into donor eggs with no chromosomes of their own.

The resulting egg would have DNA from two females and, when fertilised with a sperm, would result in an embryo which has three genetic parents. In the latest study, four healthy macaque monkeys have been born using the technique.

The scientists involved said yesterday there is no evidence that the procedure was unsafe and they were planning to apply for ethical approval to conduct clinical trials in humans within a few years.

Conventional gene therapy has been tried in humans for 20 years but changing the DNA of mitochrondria would raise ethical concerns, said Shoukhrat Mitalipov, of Oregon Health and Science University in Beaverton, Oregon.

"This type involves replacing genes in the germline which will of course transmit it to the next generation and there are concerns," Dr Mitalipov said, adding: "We are talking of gene defects that cause terrible diseases."

- INDEPENDENT