Figure 1.

Levels of Aβ in the insoluble fractions of human brains of various age. Aβ40 (open squares) and Aβ42 (shaded circles) were extracted from the insoluble fractions of 105 normal brains using a guanidine-HCl extraction protocol and quantified by ELISA. The values obtained are plotted as function of age at the time of the patient’s death. Both Aβ40 and Aβ42 were detected in all brains tested, even in those from patients as young as 20 to 30 years of age. The incidence of significant accumulation of Aβ increased age-dependently. Note that y axis is a log scale, and thus levels of Aβ42 increased much more steeply than those of Aβ40.