Francisco Lopera’s travels in the Andes began to solve a great mystery

Every ounce of his energy went into that promise. But it was hard to keep. Alzheimer’s was incurable. By his count, more than 800 drugs had been tried on it, to no effect. It was a sly disease, asymptomatic for as much as 30 years, but all that time sticky plaques of amyloid protein, rubbish as he thought of it, were being laid down in the brain, and neurons were dying. Silently, the patient—his grandmother—was being destroyed. First she forgot small things, then how to cook, then who she was. When dementia set in, she would not even know she had it. But her family would be exhausted and devastated.