PSEN1 and Alzheimer disease: In addition to PSEN1, PSEN2 can also act as the catalytic subunit in the γ-secretase complex (Zhang et al. 2000; Meckler and Checler 2016), but PSEN1 has been the main focus in studies regarding neuronal Aβ production, since mutations in PSEN1 lead to earlier onset and clinically more severe AD compared to PSEN2 (Kabir et al. 2020; Herreman et al. 1999).