MAPT and Mental deterioration: For example, only 2 studies, both published in the past year, have examined APOE4’s modification of the associations of 2 select blood-based AD and neurodegenerative markers, plasma p-tau and NfL levels.22,23 One of the studies was a small clinical study23 on the associations of plasma p-tau181, p-tau231, and GFAP with cognitive decline.