Moreover, the expression level of SH-SY5Y cyclin D1 was also increased after treatment with Aβ1-42, suggesting that Aβ activation of the Ras-ERK signaling pathway may be one of the mechanisms by which Aβ induces cell cycle disorders and apoptosis, leading to neurodegeneration and neuronal loss in AD. This evidence concerns the gene CCND1 and Alzheimer disease.