However, in tauopathies such as AD, as well as in hibernation, tau undergoes hyperphosphorylation catalyzed by various protein kinases, including but not limited to glycogen GSK3β, cyclin-dependent kinase 5 (CDK5), and protein kinase A (PKA) [103–105], accumulating an excess of 7-10 phosphate groups [106]. Here, CDK5 is linked to Alzheimer disease.