What causes Alzheimer's? Study puts leading theory to 'ultimate test'

A doctor points to PET scan results that are part of Alzheimer's disease research. Much work in the field focuses a substance called beta-amyloid. A new study could test whether that's the right target. (Evan Vucci/AP)

An idea that has propelled Alzheimer's research for more than 30 years is approaching its day of reckoning.

Scientists are launching a study designed to make or break the hypothesis that Alzheimer's is caused by a sticky substance called beta-amyloid. The study will give an experimental anti-amyloid drug to people as young as 18 who have gene mutations that often cause Alzheimer's to appear in their 30s or 40s.