Using CRISPR, which makes it possible to snip DNA open at a precisely chosen spot, a team at the hospital had modified his cells in a dish, cutting through the extra exon. When DNA is broken this way, a cell races to make a repair, but the natural repair process typically makes a small error. This causes the unwanted genetic instructions to become unintelligible. The editing process required only a single step and had taken three days. In an image taken with a microscope, his cells were clouded with green puffs of perfect dystrophin.
“I try to be realistic with my expectations,” says Dupree. “But that gave me a sense of ‘Wow, this is here.'”
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