Glial fibrillary acidic protein (GFAP), neurofilament light chain (NfL), phosphorylated tau (p‐tau)181 and amyloid beta (Aβ)42/40 were measured using ultra‐sensitive Simoa immunoassays in 44 healthy controls and 480 participants diagnosed with Alzheimer's disease/mild cognitive impairment (AD/MCI), Parkinson's disease (PD), frontotemporal dementia (FTD) spectrum disorders, or cerebrovascular disease (CVD). The gene discussed is GFAP; the disease is early-onset autosomal dominant Alzheimer disease.