Last year, Verve Therapeutics started the first human trial of a CRISPR treatment that could benefit most people—a signal that gene editing may be ready to go mainstream.

Gene-editing treatments work by directly altering the DNA in a genome. The first generation of CRISPR technology essentially makes cuts in the DNA. Cells repair these cuts, and this process usually stops a harmful genetic mutation from having an effect.

Newer forms of CRISPR work in slightly different ways. Take base editing, which some describe as “CRISPR 2.0.” This technique targets the core building blocks of DNA, which are called bases.

There are four DNA bases: A, T, C, and G. Instead of cutting the DNA, CRISPR 2.0 machinery can convert one base letter into another. Base editing can swap a C for a T, or an A for a G. “It’s no longer acting like scissors, but more like a pencil and eraser,” says Musunuru.

In theory, base editing should be safer than the original form of CRISPR gene editing. Because the DNA is not being cut, there’s less chance that you’ll accidentally excise an important gene, or that the DNA will come back together in the wrong way.

And then there’s prime editing, or “CRISPR 3.0.” This technique allows scientists to replace bits of DNA or insert new chunks of genetic code. It has only been around for a few years and is still being explored in lab animals. But its potential is huge.

That’s because prime editing vastly expands the options. “CRISPR 1.0” and base editing are somewhat limited—you can only use them in situations where cutting DNA or changing a single letter would be useful. Prime editing could allow scientists to insert entirely new genes into a person’s genome.

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