/ 5 April 2005

‘Editing’ technique can rewrite genes

Scientists have developed a potentially revolutionary technique to permanently rewrite any gene in the human body. The breakthrough brings hope to millions of people with genetic diseases but campaigners have warned that the technology could be abused by parents who want to alter the physical characteristics of their children after they are born.

Scientists at a company in California have developed a potentially revolutionary technique to permanently rewrite any gene in the human body.

The breakthrough brings hope to millions of people with genetic diseases — such as sickle-cell anaemia — but campaigners have warned that the technology, called gene editing, could be abused by parents who want to alter the physical characteristics of their children after they are born.

The scientists, at Sangamo Biosciences, have used the technique to correct mistakes in a gene that causes a rare genetic disease called X-linked severe combined immune deficiency (Scid) — so-called bubble boy disease. Sufferers never develop a fully working immune system and usually die within 18 months of birth.

Doctor Edward Lanphier, the president of Sangamo, said: ”We can target any gene we want, go into human cells and correct mistakes. These results highlight the potential for gene correction therapy for human monogenic disorders, those diseases caused by mutation of a single gene.”

The first applications were likely to be for blood diseases, Lanphier said.

The technique can also target and destroy genes. Clinical trials of its ability to stop HIV infecting immune system cells will start in humans next year.

Gene editing exploits the body’s natural ability to repair broken strands of DNA, the blueprint cells use to churn out thousands of proteins.

The scientists combined a molecule called a zinc finger protein, which can identify and bind to a specified gene, with an enzyme that can cut DNA. The protein effectively delivers the enzyme to its target, just in front of the gene the scientists want to cut out.

The scientists fool the cell into using their chosen gene in repairing the cut DNA strands, rather than a new version of the faulty one, by supplying a DNA template for it to copy. Sir Aaron Klug, the Nobel prize-winning scientist who discovered zinc finger proteins, said: ”For years scientists have been searching for a way to modify, or edit, the genome of plants and animals in a precise and predictable fashion.

”This work is, therefore, truly a landmark study that provides the foundation for gene modification without the safety issues that have plagued many traditional gene therapy applications.”

Conventional gene therapy inserts a correct version of a faulty gene into a patient’s DNA. It is difficult to control and has resulted in several high-profile deaths.

In laboratory tests, the gene editing technique successfully replaced the faulty X-linked Scid gene with a working version in 18% of human cells.

According to Sangamo, this could be enough to cure some Scid patients.

The results appear today in the online version of the journal Nature.

Dr Lanphier admitted the technique could target and change genes not involved in disease, such as those that control eye and hair colour.

”The technology is very flexible and does lend itself to those sorts of questions,” he said. ”But I think the reality is that … the people who apply it will do so for medical reasons.”

Sue Mayer, of the group Genewatch UK, called for regulation to stop gene editing being used for ”trivial” changes. ”We sometimes overstate how many people would want to use it for that, but unless there are safeguards in place the temptation will always be there,” she said. — Guardian Unlimited Â