Longitudinal stability of CSF tau levels in Alzheimer patients

Background: Antemortem levels of tau in the cerebrospinal fluid (CSF) of Al zheimer's disease (RD) patients have: repeatedly been demonstrated to be el evated when compared to controls. Although CSF tau has been reported to be elevated even in very mild AD, it is unknown how tau levels change during t he course of the disease. Methods: We have followed 29 mild-to-moderately affected AD subjects over 2 years with repeated CSF taps. Clinical measures of dementia severity (Clin ical Dementia Rating Scale, Global Deterioration Scale and Mini-Mental Stat us Examination) were obtained at the start and conclusion of the observatio n period, and CSF tau was measured with a standard enzyme-linked immunoabso rbent assay (ELISA) using two monoclonal antibodies. Results: Despite significant changes in the clinical measures consistent wi th progression of the disease, no significant overall change in CSF tau lev els (548 +/- 355 vs. 557 +/- 275 pg/mL, NS) was observed None of the clinic al variables was significantly correlated with either baseline measures of CSI; tau or delta CSF tau (last-first). Similarly, CSF tau at baseline and changes over time were not significantly related to Apolipoprotein E (APO E ) phenotype. Conclusions: These data suggest that CSF tau levels are stable over extende d periods of time in a group of mild-to-moderately demented AD subjects and that CSF tau levels do not predict the severity or rate of progression of AD, at least not during the middle stages of the illness.