Hyperactivity of Cdk5/p25 contributes to the pathologic progression of several degenerative diseases by phosphorylation different relevant substrates, e.g., tau, neurofilament proteins, and β-amyloid precursor protein related to AD, MEF2D, synuclein, Parkin, and Prx2 related to PD (Su and Tsai, 2011). This evidence concerns the gene MEF2D and neurodegenerative disease.