GFAP and Parkinson disease: Extensive studies have shown a relationship between AD-related biomarkers (β-amyloid (Aβ) 42, Aβ42/Aβ40 ratio, total tau (T-tau), phosphorylated tau181 (p-tau181), and glial fibrillary acidic protein (GFAP)) and cognitive impairment in patients with PD [4,5,6,7].