Enlarged early endosomes are also observed in induced pluripotent stem cell (iPSC) derived neurons from sporadic AD patients (Israel et al., 2012) and iPSC lines with APP and presenilin 1 (PSEN1) mutations, both genetic risk factors for early-onset AD (Kwart et al., 2019; Lacour et al., 2019). Here, PSEN1 is linked to Alzheimer disease.