The exact cause of these differences is not known, and may relate to different cells, promoters and expression levels, mouse lines, specific mutations in PS1 used, etc. In any case, it is clear that disturbed UPR signaling is not a common feature of PS1 mutations and, in addition, it is elusive whether UPR signaling is activated and involved in the pathogenesis of AD in PS1 mutation carriers. The gene discussed is PSEN1; the disease is Alzheimer disease.