NEFL and Alzheimer disease: Because plasma Aβ40, Aβ42, and Aβ42/40 levels showed limited correlations with plasma GFAP, NfL, and p-tau 181 levels compared with those of AD patients, the dynamics of plasma Aβ42/40 in PD may differ from those of amyloid PET and CSF Aβ42/40.