As previously reported4,7, participants with DS and prodromal AD and AD dementia showed a decrease in the CSF ratio of Aβ1-42/1-40 and an increase in CSF concentration of total tau, p-tau181 and NfL, as well as an increase in plasma concentration of NfL compared with asymptomatic subjects and euploid controls (Table 1). Here, MAPT is linked to Alzheimer disease.