Elevated plasma GFAP predicted increased risk of conversion to MCI (HR = 2.19, p < 0.001; adjusted HR = 1.70, p = 0.0056) and AD dementia (HR = 3.5; adjusted HR = 2.49 both p < 0.001).<h4>Conclusion</h4>Plasma GFAP is a sensitive, minimally invasive biomarker with diagnostic relevance for amyloid detection and prognostic relevance for clinical progression in early AD. This evidence concerns the gene GFAP and Alzheimer disease.