Last year, Kyle and Nicole Muldoon welcomed their baby KJ into the world. Almost immediately, doctors realized something was wrong. KJ had been born with a genetic mutation that made it impossible to regulate the amount of ammonia in his system. The rare disease had the potential to kill him or cause severe brain damage.

But KJ is almost 10 months old today. And he’s doing better than ever. Because this little baby has become a piece of medical history: the first patient of any age to receive a personalized gene-editing treatment. It's truly remarkable. In the hundreds of years of modern science, no human being had ever received a medicine designed specifically to correct their genetic mutation. A medicine built for one. That is, until KJ Muldoon.

Today, we have a very special guest: Dr. Kiran Musunuru, the gene-editing researcher at the University of Pennsylvania at the center of this breakthrough. We talk about the full story of saving baby KJ, what this breakthrough means for science, and what we need to learn or change to make personalized genetic medicine possible at a larger scale.

If you have questions, observations, or ideas for future episodes, email us at [email protected].

Host: Derek Thompson

Guest: Dr. Kiran Musunuru

Producer: Devon Baroldi

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