Mechanistic studies of the sortilin-related receptor 1 (SORL1) gene, which encodes a regulator of protein trafficking between the trans-Golgi network and endosomes, including amyloid precursor protein (APP) (Andersen et al., 2005; Mehmedbasic et al., 2015; Rogaeva et al., 2007; Young et al., 2015), provide an opportunity to analyze a pathogenic cellular pathway common to both monogenic and sporadic AD. Here, APP is linked to Alzheimer disease.