CDK5 and Alzheimer disease: Tau has 85 phosphorylatable residues (45 of which found in AD brains) (Oliveira et al. 2017); however, it has been demonstrated that residue Thr231 is the primary phosphorylation site for GSK-3β and other kinases, such as cdk5, critical for tau hyperphosphorylation, and phosphorylation at this residue can destabilize tau-binding to microtubules and promote tau aggregation (Lin et al. 2007) The effect of Aβ in modulating protein kinases such as GSK-3β and cdk5 is well established, and these kinases are believed to directly contribute to tau hyperphosphorylation (Oliveira et al. 2015).