In addition, plasma p‐tau181 levels were significantly associated with the volume of the basal forebrain, plasma NfL levels, the CSF Aβ1‐42 to Aβ1‐40 ratio, CSF t‐tau, CSF p‐tau181, CSF NfL concentrations, gray matter volume loss, and the atrophy of characteristic AD regions measured by MRI, including the temporal angular gyrus, supramarginal gyrus, and precuneus in both hemispheres.41, 49, 70. This evidence concerns the gene NEFL and Alzheimer disease.