CDK5 and Alzheimer disease: Interestingly, protein lysates from human AD cortex and animal models of AD show hyperphosphorylation of CRMP-2 at residues Thr509, Thr514, and Ser518 which are known to be the GSK-3β phosphorylation sites as well as Ser522, the well-known Cdk5 phosphorylation site (for review see [78]).