Background: In brains with AD, Abeta is a major component of diffuse plaques. Previous reports showed that CSF Abeta42 levels were lower in patients with AD than in controls. Although studies showed higher plasma Abeta42 levels in familial AD, a recent report has indicated that plasma Abeta42 levels were similar in a sporadic AD group and controls. However, no information is published on plasma Abeta40 and Abeta42 levels in relation to Apo E genotype or severity of dementia in sporadic AD.
Objective: To examine plasma and cerebrospinal fluid (CSF) levels of amyloid beta protein 1-40 (Abeta40) and 1-42 (Abeta42) levels in patients with probable Alzheimer disease (AD) and elderly nondemented control subjects in relation to the apolipoprotein E (Apo E) genotype and dementia severity.
Setting: Two university medical centers.
Patients and methods: Levels of Abeta40 and Abeta42 were measured in plasma from 78 patients with AD and 61 controls and in CSF from 36 patients with AD and 29 controls by means of a sandwich enzyme-linked immunosorbent assay.
Results: Mean plasma Abeta40 levels were higher in the AD group than in controls (P = .005), but there was substantial overlap; Abeta42 levels were similar between the groups. Levels of Abeta40 and Abeta42 showed no association with sex or Mini-Mental State Examination scores. There was a significant relationship between age and Abeta40 level in controls but not in the AD group. Levels of Abeta40 were higher in patients with AD with the Apo E epsilon4 allele than in controls (P<.01). Cerebrospinal fluid Abeta40 levels were similar in the AD group and controls. However, Abeta42 levels were lower in the AD group than in controls (P<.001). The levels showed no association with severity of dementia.
Conclusions: Although mean plasma Abeta40 levels are elevated in sporadic AD and influenced by Apo E genotype, measurement of plasma Abeta40 levels is not useful to support the clinical diagnosis of AD. Lower levels of CSF Abeta42 in the AD group are consistent with previous studies.