Objectives: Decreased levels of A beta(1-42) are found in CSF of patients w
ith AD. Because early stages of Creutzfeldt-Jakob disease (CJD) and AD shar
e several clinical features, we investigated A beta(1-42) levels in CSF of
these groups, inferring that this might give additional help in differentia
ting patients with CJD from AD patients. Methods: We investigated 27 patien
ts with CJD, 14 patients with AD, 19 patients with other dementias, and 20
nondemented controls (NDC) for A beta(1-42) in CSF. Twenty-four of the 27 C
JD patients were neuropathologically verified. All the neuropathologically
verified patients presented with a type 1 prion protein pattern. CJD patien
ts were all homozygous for methionine at codon 129. Except in five CJD pati
ents, no beta-amyloid plaques were seen. Additionally, APOE status was dete
rmined in patients with CJD. Results: Levels of A beta(1-42) in CSF were de
creased in patients with AD as well as in CJD. Levels of A beta(1-42) in CS
F of patients with CJD and AD were significantly different from the other d
ementia and NDC groups. There was no substantial difference between the CJD
and AD groups (p = 0.66). Decreased levels of A beta(1-42) did not correla
te with the APOE epsilon 4 load in patients with CJD. Conclusion: Low level
s of A beta(1-42) in CSF do not exclude a diagnosis of CJD. Decreased level
s of A beta(1-42) in CSF can occur without p-amyloid plaque formation in th
e brain. However, the underlying mechanism of this phenomenon must be eluci
dated.