APP and Alzheimer disease: Stimulation of mTOR signalling has been observed in response to accumulation of Aβ (Caccamo et al., 2010), and hyperactivation of mTOR is observed in Down's syndrome (in which the dosage of the APP gene is increased because it resides on chromosome 21 and early-onset AD is common) (Bordi et al., 2019; Iyer et al., 2014).