Amyloid-β 42 Plasma Levels are Elevated in Amnestic Mild Cognitive Impairment

Amnestic mild cognitive impairment (aMCI) is considered a prodromal stage of Alzheimer's disease (AD). We measured plasma levels of amyloid-β₄₀ (Aβ₄₀) and Aβ₄₂ in 191 subjects with aMCI. Seventy-nine of them were clinically followed for two years. In the total cohort of aMCI cases, the average level of Aβ₄₂, as well as the Aβ₄₂/Aβ₄₀ ratio, was significantly higher than those of the 102 cognitively normal age-matched subjects. The aMCI cases that converted to probable AD within 2 years had higher levels of Aβ₄₂ and, to a lesser extent, Aβ₄₀ than the stable cases. However the large variability of measured values indicates that plasma Aβ is not a suitable marker of incipient AD.