The classification system divides preclinical Alzheimer's into three stages:
Stage 1: Levels of amyloid beta, a protein fragment produced by the brain, begin to fall in the spinal fluid. This indicates that the substance is beginning to form plaques in the brain.
Stage 2: Levels of tau protein start to rise in the spinal fluid, indicating that brain cells are beginning to die. Amyloid beta levels are still abnormal and may continue to fall.
Stage 3: In the presence of abnormal amyloid and tau biomarker levels, subtle cognitive changes can be detected by neuropsychological testing. By themselves, these changes cannot establish a clinical diagnosis of dementia.
The researchers applied these criteria to research participants studied from 1998 through 2011 at the Knight Alzheimer Disease Research Center. The center annually collects extensive cognitive, biomarker and other health data on normal and cognitively impaired volunteers for use in Alzheimer's studies.
The scientists analyzed information on 311 individuals age 65 or older who were cognitively normal when first evaluated. Each participant was evaluated annually at the center at least twice; the participant in this study with the most data had been followed for 15 years.
At the initial testing, 41 percent of the participants had no indicators of Alzheimer's disease (stage 0); 15 percent were in stage 1 of preclinical disease; 12 percent were in stage 2; and 4 percent were in stage 3. The remaining part
|Contact: Michael C. Purdy|
Washington University School of Medicine