This aligns with cross-sectional data from genetically determined Alzheimer's disease due to trisomy 21, which indicated that plasma GFAP has an inflection point approximately 10 years before onset of Alzheimer's disease in a Down syndrome cohort.26 Interestingly, in genetic frontotemporal dementia there was no presymptomatic increase in plasma GFAP and any possible increases in symptomatic phases might be mutation-specific,27 which gives further support for an Alzheimer's disease-specific increase of plasma GFAP in presymptomatic individuals. The gene discussed is GFAP; the disease is early-onset autosomal dominant Alzheimer disease.