They wanted to initially start talking about comfort care, so end-of-life care.

We had to give them an opportunity to fight.

What did you think when they brought up the idea of a gene therapy?

Kind of far-fetched, kind of stuff you hear about on, like, podcasts.

I'm Becky Quick.

This is The Path, the podcast series from CNBC Cures about the people, the powerful communities,

and the pioneers of rare disease, even the smallest pioneers.

Hi. Hi, cutie. Hi.

Hi, cutie.

Yay.

Who are all these people?

K.J. Muldoon, or baby KJ., is the first person in the world to receive a personalized

CRISPR-based gene editing therapy.

He is the whole data set. He's one of a kind,

and he is a success story of modern medicine, a hopeful sign for any of the 30 million Americans

impacted by the thousands of rare diseases and conditions. Rare can mean a lot of things.

These conditions can be misdirections and neuro pathways, deficits of critical proteins or enzymes,

sort of genetic typos, biological chances that impact small patient populations, and 95% of rare diseases lack a cure.

He looks like such a happy boy.

Born with the rare genetic deficiency, CPS1, KJ was just hours old when it became clear that

a severe enzyme deficiency was preventing his liver from working properly.

This condition is so rare that it affects just one child out of every 1.3 million babies, and most don't survive long enough for a liver transplant,

...