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Her most important slide showed decreases in the level of mutant huntingtin in trial participants’ CSF — indicative of reduced levels of the toxic protein in their brains — that were proportional to the amounts of drug the volunteers had received. At the two highest doses, production of the protein had, on average, decreased by about 40%.

“People started crying,” says Jeff Carroll, a neuroscientist who investigates Huntington’s disease at Western Washington University in Bellingham. “Everybody who works in Huntington’s disease long enough meets families and gets to know them, so it becomes very personal.”

Carroll’s connection to his work runs particularly deep. He began his career in neuroscience after his mother was diagnosed with Huntington’s disease. Then, in 2003, he discovered that he, too, had the mutation for the condition. Looking at Tabrizi’s slide, Carroll thought, “This is a graph that is changing my life.”