CDK4 and Alzheimer disease: The Cdk inhibitor p16INK4a is elevated in AD and is associated with neurofibrillary degeneration [129], as well as other members of the INK4-family of cyclin-dependent kinase inhibitors such as p15INK4b, p18INK4c and p19INK4d that bind directly to Cdk4/6 or to complexes of Cdk4/6 with D-type cyclins [130].