A breakthrough to help victims of genetic conditions was announced by scientists. Picture: File

London - A breakthrough to help victims of genetic conditions was announced by scientists.

They said the DNA-editing technique has the potential to fix up to 89% of the mutations that lead to deadly and life-long illnesses.

They have already successfully reversed the mutation which causes sickle cell anaemia.

The procedure works by targeting the "double-helix" which makes up our DNA, containing long chains of chemicals called cytosine, guanine, adenine and thymine – the letters C, G, A and T. These letters, which appear six billion times throughout our cells, need only a single A to change into a T to cause sickle cell anaemia.

Scientists, led by the Broad Institute in Massachusetts, were able to change the T back to an A, and also to remove the four letters in DNA which cause Tay-Sachs disease. The rare genetic condition, which mainly affects babies and young children, stops the nerves working properly and is usually fatal.

The "prime editing" method has been likened to word processing because it rewrites the genetic code. It could also work in a potentially safer way than the first type of gene-editing, Crispr-Cas9. This is because it avoids cutting the double-helix, which can cause unwanted changes to genes.

The scientists report making more than 175 different gene edits in the laboratory, targeting all 12 types of single-letter genetic mutation that cause illness.

In theory the new methods could fix almost 90% of the 75 000-plus known disease mutations. However more research is needed to see if they work in humans.

Professor David Liu, senior author of the study, said: "A major aspiration in the molecular life sciences is the ability to precisely make any change to the genome in any location. We think prime editing brings us closer to that goal." 

Earlier this year it was reported that scientists had treated a patient with sickle cell disease by editing her DNA using Crispr-Cas9. This snips out the error in the genetic code before replacing it with the correct letters – however it can cut in the wrong place.

It can also add extra DNA material or miss out important genetic code. These might cause harmful side effects.

"You can think of prime editors as being like word processors capable of searching for target DNA sequences and precisely replacing them with edited DNA sequences," Professor Liu told The Guardian. 

"Potential impacts include being able to directly correct a much larger fraction of the mutations that cause genetic diseases, and being able to introduce DNA changes into crops that result in healthier or more sustainable foods."

The research was reported in the journal Nature.

Daily Mail