PER2 and Alzheimer disease: Our finding that AD-related genes [32–36], including Egr2, Fos, Arc, Hmgcr, Nuak1, Egr1, Hap1, Per2. Egr2, Fos, Arc, and Hmgcr, show significant differential expression in noise-exposed mice lends support to the idea that environmental hazards including noise exposure may promote the occurrence and development of AD.