This is most likely reflective of side effects of overdosed BACE1 inhibitor drugs given that the Icelandic mutation (A673T) in the amyloid-β precursor protein (APP) gene resulting in only ~30% lifelong reduction of Aβ is protective against AD and age-related cognitive decline (Jonsson et al., 2012; Martiskainen et al., 2017). Here, APP is linked to Alzheimer disease.