To investigate the unique etiological parallels between DS and AD, we measured the levels of Aβ and tau prions in frontal brain cortices of 28 deceased patients with DS who ranged from age 19 to 65 y (median age, 51 y; SI Appendix, Table S1) and 14 deceased control cases with no cognitive impairment, who ranged in age from 27 to 70 y (median age, 48 y; SI Appendix, Table S1). Here, MAPT is linked to Alzheimer disease.