APOE and Cognitive impairment: Though a relatively small number of participants in this initially cognitively normal sample progressed to clinical states of impairment (23 of 236, 9.7%; 20 to Mild Cognitive Impairment and 3 to AD dementia), we observed that higher plasma NT1 levels at study baseline were strongly associated with clinical progression (t(230) = −4.03, p < 0.0005; corrected for age, sex, ApoE ε4 status, and length of follow-up; Fig. 1c).