https://www.wired.com/story/a-new-crispr-technique-could-fix-many-more-genetic-diseases/

Andrew Anzalone was restless. It was late fall, 2017. The year was winding down, and so was his MD/PhD program at Columbia. Trying to figure out what was next in his life, he’d taken to long, leaf-strewn walks in the West Village. One night as he paced up Hudson Street, his stomach filled with La Colombe coffee and his mind with Crispr gene editing papers, an idea began to bubble through the caffeine brume inside his brain.

Crispr, for all its DNA-snipping precision, has always been best at breaking things. But if you want to replace a faulty gene with a healthy one, things get more complicated.