As he parks next to a large white farmhouse that would fit comfortably into a 19th-century still life, Richard Kelley smiles at a rust-colored retriever, an old friend that stirs from an early spring sunbath to greet him. Kelley knows this old place well. He’s been dropping by regularly to check on Joshua since the boy was little more than a month old, when his grandmother noticed that his body quavered slightly but uncontrollably.

Kids with sickle cell disease (SCD) grow up facing a future of potential organ damage, vision problems, infections, and stroke. But perhaps the most agonizing part of living with the disease is dealing with the “crises”—unpredictable attacks of intense pain that take over little bodies, often sending them to a hospital for narcotics to curb […]