Alzheimer's decay could start earlier than thought

Alzheimer's disease is thought to be caused by the build up of tangles, or plaques, of a protein called beta amyloid in the brain. However, researchers from Washington University School of Medicine in St Louis have found that in people who have a genetic variation linked to an increased risk of Alzheimer's disease the brain can start going downill even in the absence of amyloid plaques. The researchers studied 100 people with an average age of 62. None of them had amyloid plaques or any sign of the protein in their spinal fluid but half of them had a variation in the gene APOE4 which is linked to an increased risk of Alzheimer's. The participants with the genetic variation showed different functioning in a region of the brain - centred on a structure called the precuneus - called the default mode network. This region is thought to be connected to what the brain does when it is not thinking about anything in particular - wool-gathering or day-dreaming - but is also connected to lots of other regions so a deterioration here could have widespread effects on other thought processes.