The past three decades saw a dramatic improvement in our understanding of what brings about Alzheimer’s disease. Two proteins are thought to be responsible: amyloid and tau. The most widely accepted theory is that a critical level of amyloid in the brain triggers the build-up of the more toxic tau protein. This has led to several studies testing drugs and vaccines that remove amyloid and tau to see if they can improve or even prevent dementia. Results have been disappointing.