Gene editing has become an important tool in our manipulation of DNA. While the technique has been good so far, a new breakthrough might suddenly make it a lot more useful in curing genetic diseases in humans.
The new approach allows scientists to edit out a single letter of DNA, the so-called "point-mutation," by using an enzyme that can convert one DNA base (cytosine) into another (uridine), without breaking the molecule. The technique worked on isolated DNA in test tubes 44 percent of the time. In cells, unfortunately, the success rate was only 7.7 percent, as the enzyme would change one of the strands of DNA and then the cell would correct the mismatch.
“It turns out that the majority of disease-associated human genetic variants are point mutations,” said David Liu, a chemical biologist at Harvard University, to Nature. “But current genome methods correct point mutations much less efficiently and much less cleanly than we can disrupt a gene.”
The most common technique is called CRISPR/Cas9. The technique is affordable and reliable, and it has so far proven quite successful. For example, mosquitos that can resist the malaria parasite were genetically modified using CRISPR.
The Cas9 in CRISPR/Cas9 is an enzyme used to cut a specific chunk of DNA using a guide RNA molecule selected by the scientists. Cells respond to this change by healing the break in a sloppy way, a situation the scientists count on. The change usually stops the expression of the gene.
Scientists have tried to use CRISPR/Cas9 to also insert correct DNA into the gap, but so far the technique has only been successful less than 5 percent of the time.
Liu’s team attached a different enzyme on a disabled Cas9; in doing so, it could still be delivered to the DNA, but the molecule would not be cut. In this case, the new enzyme would simply switch one DNA base for another. While the technique has a lot of potential, it is still in its infancy. As reported in the paper published in Nature, the team has already started modifying it.
By adding a new protein, the "base editor," as Liu calls it, successfully "corrected mutations associated with Alzheimer’s disease in mouse cells grown in culture with an efficiency of up to 75 percent," according to Nature. The same base editor was even able to do these types of corrections in some cancerous human cells, although with an efficiency of only 7.6 percent.
This technique could possibly lead to a cure for many diseases, and the team is currently looking into being able to change different bases, as well as being able to change multiple bases at once. It will be years before this can be applied to humans, but the gene-editing revolution is definitely within our reach.