This is potentially physiologically significant since phosphorylation of tau at Thr-231, a target site for ERK2, GSK3β, and cdk5, occurs early in AD and can further inhibit the ability of PP2A/Bα to dephosphorylate other major AD-tau phosphoepitopes (Landrieu et al., 2011). Here, PTPA is linked to Alzheimer disease.