CSF and Plasma Aβ40 and Aβ42 Levels in Down Syndrome (DS) Persons with Alzheimer Disease (AD) [DS/AD+] and Those without [DS/AD-] (P5.172)

Objective: We hypothesized that CSF Aβ42 levels will be lower in DS/AD+ than DS/AD-, and that CSF and plasma Aβ levels will not exhibit any substantial relationship. Background: Older persons with DS have neuropathological changes characteristic of AD. Studies reported increased plasma Aβ40 and Aβ42 levels in DS than age-matched normal controls. However, to our knowledge none has examined the levels in matched pair of plasma and CSF in DS/AD+, and DS/AD-, nor the relationship between the two measures. Methods: Plasma and CSF were collected from DS/AD+ (N=12; 54.4±7.8 years old) and DS/AD- (N=18; 40.4±9.6) (p<.001). Aβ40 and Aβ42 levels in the coded samples were quantitated using sandwich ELISA. All analyses were conducted using both parametric and nonparametric statistics where appropriate, in SPSS. Results: CSF Aβ42 levels were lower in DS/AD+ (172.4±61.0 pg/ml) than DS/AD- (237.2±86.7 pg/ml) (p<.033). CSF Aβ40 levels were similar in both groups (p<.918). Plasma Aβ40 levels were higher in DS/AD+ (240.6±52.7) than DS/AD- (204±35.4) (p<.03). Plasma Aβ42 levels were similar in both groups (p<.233). There was no relation between CSF and plasma Aβ40 or Aβ42 levels in either group, and these findings are consistent with patients having probable AD. Conclusions: Lower levels of CSF Aβ42 in DS/AD+ are consistent with those reported in patients with probable AD, and may be useful to predict AD in DS. The lack of relation between CSF and plasma Aβ40 or Aβ42 levels in DS suggests that the source of the synthesis of Aβ in brain and blood is different. Disclosure: Dr. Mehta has received royalty payments from Covance Labs. Dr. Fortea has nothing to disclose. Dr. Carmona Iragui has nothing to disclose. Dr. De Leon has nothing to disclose. Dr. Zigman has nothing to disclose.