Schizophrenia, which affects 1 in 100 people worldwide and an estimated 2.4 million Americans, exacts tremendous social costs and great human suffering. Drugs can calm the inner voices, delusions and hallucinations, but few patients recover fully, and there is no cure. Nor are there predictive tests or internal markers for the disease — it must be diagnosed by outward signs alone. But this problem is at last yielding to progress on the genetic front.