The levels of cerebrospinal fluid A beta 40 and A beta 42(43) are regulated age-dependently

Decreased levels of cerebrospinal fluid (CSF) A beta 42 is a diagnostic mar ker of Alzheimer' s disease. To clarify the biological basis of this marker , the physiological alterations of CSF A beta 40 and A beta 42 by aging wer e studied. CSF samples from 92 normal subjects between 8 and 89 years old w ere measured using a specific ELISA for A beta 40 and A beta 42(43). High c oncentrations of A beta 40 and A beta 42(43) in the young group, under 29 y ears old, changed to be at low concentrations in the adult group between 30 and 59 years old. Subsequently, the levels increased again with age. Third order regression analysis showed a significant correlation between the lev els of A beta 40 and age (Y = - 169 X-3 + 3.1X(2)- 0.02X + 4135; P < 0.034) and between the levels of A<beta>42(43) and age (Y = - 46 X-3 + 0.9 X-2- 0 .005X + 992; P < 0.005). The levels of CSF A<beta>40 and A beta 42(43) were physiologically regulated to show a U-shaped natural course in normal agin g. These findings suggested that the physiological increase of A beta 42(43 ) over 59 years of age is selectively inhibited in Alzheimer' s disease. (C ) 2001 Elsevier Science Inc. All rights reserved.