Last updated November 14, 2017 at 8:21 am
Scientists in the US have come up with a new way to edit DNA and RNA, called base editing, that makes the process much more precise.
It could dramatically expand the range of inherited diseases that can be treated with gene editing.
The technique, a modified form of CRISPR, is described in a paper published today in Nature. It makes it possible to individually replace all four chemical bases or “letters” of DNA – adenine (A), guanine (G), cytosine (C) and thymine (T) – without breaking the double strands that make up the code.
The human genome contains six billion of these bases which pair off, A with T and C with G.
Previously scientists have edited G-C letter pairs to make T-A pairs, but this new method allows A-T pairs to be converted to G-C pairs thanks to an enzyme called TadA. It converts adenine to a molecule called inosine which cells treat as guanine.
That potentially make it possible to address “point mutations”, where one base pair in a strand of DNA is incorrect or missing. About half of all the 32,000-known disease-related single-base-pair changes involve the conversion of a wild-type G-C base pair to a mutant A-T base pair, so the new system offers the chance to reverse many such mutations, the researchers say.
“Standard genome-editing methods, including the use of CRISPR-Cas9, make double-stranded breaks in DNA, which is especially useful when the goal is to insert or delete DNA bases,” Liu told reporters. “But when the goal is to simply fix a point mutation, base editing offers a more efficient and cleaner solution.”
The ABEs are shown to work on DNA in both bacterial and human cells. In human cells, they can introduce the desired genetic change at a wide range of target regions with an efficiency of around 50%, higher than that of other genome-editing methods, and with virtually no undesired by-products, such as random insertions, deletions or other mutations.
Research earlier this year, published in Nature Methods, highlighted the unintended side effects of CRISPR. Researchers from Stanford University, Columbia University and the University of Iowa sequenced the whole genome of mice that had previously undergone CRISPR gene editing. Two of the mice had undergone 1,500 unintended single nucleotide mutations, and more than 100 deletions and insertions of genetic material.
Related: CRISPR and human embryos