Many studies have shown that cell cycle proteins such as cyclins and CDKs are aberrantly expressed in AD brains [50–52], and CDK inhibitors p16INK4a, p15INK4b, p18INK4c and p19INK4d have also been found to be aberrantly expressed in brain neurons of AD patients [53–55]. This evidence concerns the gene CDKN2D and Alzheimer disease.