Jeff Carroll was in the Army when his mom was diagnosed with Huntington’s disease—a fatal, hereditary, neurodegenerative disorder that Carroll, a high-school dropout, had never heard of. So when he got out of the Army, he enrolled in a few university biology classes to better understand it. Huntington’s, he told me—unlike other neurodegenerative diseases such as Alzheimer’s or Parkinson’s—results from one specific genetic mutation, which the research community has known about since 1993. Carroll himself carries the mutation. “You would think, given all that knowledge, or all that time, we’d have figured it out by now,” he said. “We know a lot, but not enough, because we can’t cure anyone of H.D. yet.”