In CU individuals at risk of developing AD, GFAP predicted brain PET Aβ + (AROC = 0.76), outperforming CSF GFAP (AROC = 0.69) and other glial markers (CSF chitinase-3-like protein 1, YKL-40: AROC = 0.64; and Triggering Receptor Expressed on Myeloid Cells 2: AROC = 0.71). Here, GFAP is linked to Alzheimer disease.