Plasma GFAP was significantly higher in cognitively unimpaired Aβ-positive (CU- Aβ+), mild cognitively impaired Aβ-positive (MCI Aβ+) and Alzheimer’s disease Aβ-positive (AD Aβ+) groups (P < 0.0001) compared with cognitively unimpaired Aβ-negative (CU Aβ−) and mild cognitively impaired Aβ-negative groups (MCI Aβ−) (P < 0.0005). This evidence concerns the gene GFAP and early-onset autosomal dominant Alzheimer disease.