All plasma markers were generally poor at distinguishing MCI-AD from MCI-LB (Aβ42/40 AUC = 0.53 [0.42 to 0.64], p-tau181 = 0.62 [0.51 to 0.73], GFAP = 0.62 [0.51 to 0.72], NfL = 0.58 [0.47 to 0.69]). This evidence concerns the gene GFAP and Alzheimer disease.