(Via EurekAlert!) The rate of production and clearance of amyloid beta in the brain is actually very rapid. Excess amyloid increasingly seems to be a problem of clearing mechanisms: "Aging is the most important risk factor for neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease ... the age onset of these diseases is not simply a matter of time but that the aging process plays an active role in controlling the onset of toxicity ... Half of all people who reach age 85 will likely be affected by Alzheimer's disease, and the onset age - usually around 75 - is almost the same for all sporadic neurodegenerative aggregation diseases. ... Throughout life, brain cells produce aggregation-prone beta-amyloid fragments that must be cleared. ... This process is very efficient when we are young but as we get older it gets progressively less efficient ... In individuals who carry early onset Alzheimer's-linked mutation, an increased 'aggregation challenge' leads to clearance failure and the emergence of Alzheimer's much earlier."