Extreme CSF Aβ levels identify familial eoAD and loAD PSEN1 mutations and, thus, can be useful endophenotypes for genetic AD [155] as well as for children with Down syndrome [156], but inverse relations between in vivo amyloid imaging load in human brain and CSF Aβ-42 have been found [103]. Here, PSEN1 is linked to Alzheimer disease.