CDK5 and Alzheimer disease: A wide range of proline-directed kinases (e.g., glycogen synthase kinase 3 β (GSK3β) (Llorens-Martín et al., 2014), cyclin-dependent kinase 5 (CDK5) (Kimura et al., 2014)), nonproline-directed kinases (e.g., tau-tubulin kinases (TTBK) (Tomizawa et al., 2001)), microtubule affinity regulated kinases (e.g., MARK) (Matenia and Mandelkow, 2009) and tyrosine kinases (e.g., Fyn and Abl (Lee et al., 2004; Derkinderen et al., 2005)) have been found to phosphorylate tau and contribute to the pathophysiological hallmark of AD.