GFAP and hippocampal atrophy: In DS individuals, plasma NfL levels were significantly correlated with CSF NfL,39 basal forebrain volumes,41 longitudinal dementia status,69 gray matter volume loss,49 amyloid pathology and hippocampal atrophy,57 white matter hyperintensity volume,50 plasma p‐tau217, p‐tau181, and GFAP.50, 56