Tau protein in cerebrospinal fluid: a new diagnostic and prognostic marker in Alzheimer disease?

Tau is the main protein of paired helical filaments. It can be detected and measured in cerebrospinal fluid (CSF) and for this reason it has been proposed as a possible in vivo marker of Alzheimer disease (AD). To evaluate the usefulness of CSF tau in the diagnosis of AD we measured it in patients with AD, frontal lobe dementia (FLD), vascular dementia (VD), and in healthy controls by means of a specific enzyme-linked immunosorbent assay test. Individuals with AD had significantly higher tau levels than FLD, VD, and controls. Individuals with late onset AD had significantly higher levels than those with early onset disease. In AD, CSF tau level did not correlate with age, duration, or severity of the disease, whereas a correlation with age was found in FLD and controls. In the nine AD patients in whom CSF tau measurement was repeated after 2 years, mean levels did not differ from baseline, although a worsening of cognitive performances occurred. The overlap among the different groups and the absence of any modification over time suggest that CSF tau measurement, more than in confirming or staging overt AD, might be useful in revealing the disease at its preclinical phase.