PSEN2 and Alzheimer disease: Although the processes of AD could be triggered by many environmental factors, previous studies also suggested that genetic polymorphisms play an important role in AD, among which mutations in amyloid precursor protein (APP), presenilin‐1 (PSEN1), presenilin‐2 (PSEN2) and apolipoprotein E (APOE) have been proved to be associated with AD risk 2.