Recently, Rab21 has been identified as a novel interactor of PS1, one of the key secretases for hydrolyzing APP protein to produce beta-amyloid (Aβ) and regulate the activity of PS1 by transferring it from early endosome to late endosome/lysosome, suggesting its crucial role in the neuropathogenesis of AD [20]. This evidence concerns the gene RAB21 and Alzheimer disease.