Initial findings from an analysis of cerebrospinal fluid taken between 1995 and 2005 from 265 middle-aged healthy volunteers, of whom 75% had a close family member with Alzheimer’s disease, has found that the ratios of phosphorylated tau and amyloid-beta could predict mild cognitive impairment more than five years before symptom onset — the more tau and less amyloid-beta, the more likely MCI will develop. The rate of change in the ratio over time was also predictive — the more rapidly the ratio of tau to amyloid-beta went up, the more likely the eventual development of MCI.
The drop in amyloid-beta is thought to be because it is getting trapped in the plaques characteristic of Alzheimer’s.
 . CSF biomarker changes precede symptom onset of mild cognitive impairment. Neurology [Internet]. 2013 . Available from: http://www.neurology.org/content/early/2013/10/16/01.wnl.0000435558.98447.17