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.
All studies in dementia patients have failed to show improvements, even if amyloid itself was affected. In a prominent case, a vaccine given to patients was shown to have cleared the brain of amyloid of people who nonetheless died of profound dementia.
Over the same period, studies in people destined to develop the condition because of a genetic mutation reported that the changes leading to dementia begin up to 25 years before any symptoms. One logical interpretation is that attempts to find a cure for dementia may have failed because the patients in drug trials were treated too late in the disease process.
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