Side Effects May Include … A Completely New Hair Color?

^{Photo by ANIRUDH on Unsplash}

In October 2019, Jordan Janz became the first person in the world to receive an experimental therapy for cystinosis, a rare genetic disease. The treatment was physically grueling. Doctors extracted blood stem cells from Janz’s bone marrow and genetically modified them in a lab. Meanwhile, he underwent chemotherapy to clear out the remaining faulty cells in his bone marrow before he got the newly modified ones. The chemo gave Janz sores in his mouth so painful that he couldn’t eat. He lost his head full of pale-blond hair.

But Janz, then a 20-year-old from Alberta, Canada, had signed up for this because he knew that cystinosis was slowly killing him. The mutated gene behind this disease was causing toxic crystals of a molecule called cystine to build up everywhere in his body. He threw up constantly as a kid. Visible crystals accumulated in his eyes. And his kidneys were now failing. Cystinosis patients live, on average, to 28.5 years old.

Fortunately, the experimental gene therapy seemed to work; Janz began to feel better. His...