11 November 2013

Dr Anna Cauldwell By

Appeared in BioNews 730

A molecular technique that enables any part of the human genome to be altered with extreme precision has been hailed by scientists as a breakthrough in genetics. It is the first time researchers have been able to engineer any part of the genome without introducing mutations, reports The Independent.

'This is really a triumph of basic science', Professor Craig Mello, University of Massachusetts Medical School professor and joint recipient of a Nobel Prize in 2006 for a previous genetic discovery, told The Independent. 'It's a tremendous breakthrough with huge implications for molecular genetics'.

Crispr was originally discovered in bacteria by Japanese researchers in 1987. However, it was largely dismissed by scientists as 'junk DNA' until 2012 when Professor Jennifer Doudna, University of California, Berkeley, uncovered its potential.

Crispr uses an RNA guide molecule that can be programmed to match any unique DNA sequence. This guide is attached to a special enzyme that finds the target sequence of DNA and cuts both DNA strands in the double helix. This then allows copied DNA to be inserted into the genome and defective DNA to be deleted.

Previous gene therapy techniques have made use of less accurate methods that often require the use of a modified virus that inserts DNA at random in the genome, leading to safety concerns.

The Independent reports that some experts have predicted Crispr may soon be used in human gene therapy trials to treat incurable viruses such as HIV or untreatable genetic disorders such as Huntington's disease. Crispr could also be used to potentially correct gene defects in human embryos in IVF, Professor Mello added, although the use of an embryo that has been genetically altered in IVF remains illegal in the UK.

While the development has been widely welcomed by the scientific community, some experts have emphasised that it may be too soon to call its benefits. Professor Dagan Wells, University of Oxford, said: 'I think it's important to stress that the therapeutic potential of this sort of genetic microsurgery is yet to be proven. Additionally, a significant amount of work will need to be done to assess the safety of the method before it can be used clinically'.

Professor Robin Lovell-Badge, MRC National Institute for Medical Research, said while there was much deserved excitement surrounding the technique, 'hype needs to be tempered with a little caution'.

'Although remarkably efficient compared to other techniques, the genetic changes introduced by the Crispr technique are not always as perfect as designed and on occasion it could introduce problems that are just as worse as the one being corrected', he said.

On its potential application to IVF, Professor Peter Braude, Emeritus Professor of Obstetrics and Gynaecology at King's College London, said although the news was 'fascinating', the technique still had a long way to go in relation to IVF.

'For almost all known genetic diseases there is always a proportion of embryos that do not contain the mutation and thus can be selected for by preimplantation genetic diagnosis, a relatively modest modification of the IVF technique without the need for genetic manipulation'.

'Germ line therapy still has a long way to go before it is more widely accepted, both in terms of safety evaluation, and ethics of appropriateness of use', he said.