en Cellular and molecular Neuroscience Cellular and molecular Neuroscience Review Review Dementia is a progressive disorder that leads to memory loss and cognition impairment and affects daily function. Alzheimer disease (AD) is the main cause of dementia that characterized by loss of memory and cognition. AD pathologically is demonstrated by neuronal atrophy, synapse loss and the unusual reposition of amyloid-&beta; protein (A&beta;) as senile plaques and hyperphosphorylated tau protein as neurofibrillary tangles (NFT). Tau is a microtubule associated protein mostly expressed in neurons. Site-specific phosphorylation regulates Tau function. In AD, the six adult tau isoforms are unusually phosphorylated that cause to form the paired helical filament. The different conditions of tau phosphorylation eventuate from the function of specific kinases and phosphatases. In recent years some biomarkers such as phospho tau 181, 199 and 231 had been assessed in cerebrospinal fluid&nbsp; &nbsp;(CSF) and blood and had been showed their elevation in AD. This article provides an overview of tau structure, functions, and its involvement in AD and its role as a CSF biomarker.<br> &nbsp; Alzheimer, Tau, Phospho tau, Dementia,CSF biomarker, NFT 0 0 http://bcn.iums.ac.ir/browse.php?a_code=A-10-1136-3&slc_lang=en&sid=1 nahid Ahmadian ahmadiannahid@gmail.com 13700319475328460051341 13700319475328460051341 No Tabriz University of Medical Sciences, Neurosciences Research Center (NSRC), Tabriz, Iran Mahnaz Talebi Talebi511@yahoo.com 13700319475328460051342 13700319475328460051342 Yes Tabriz University of Medical Sciences, Neurosciences Research Center (NSRC), Tabriz, Iran Javad Mahmoudi mahmoudi2044@yahoo.com 13700319475328460051343 13700319475328460051343 No Tabriz University of Medical Sciences, Neurosciences Research Center (NSRC), Tabriz, Iran Saeed sadig etegad saeed.sadigetegad@gmail.com 13700319475328460051344 13700319475328460051344 No Tabriz University of Medical Sciences, Neurosciences Research Center (NSRC), Tabriz, Iran Alireza Aghili Talebi511@yahoo.com 13700319475328460051345 13700319475328460051345 No Tabriz University of Medical Sciences, Neurosciences Research Center (NSRC), Tabriz, Iran