MAPT and early-onset autosomal dominant Alzheimer disease: Cerebrospinal fluid (CSF) levels of amyloid peptide β with 42 amino acids (Aβ42), tau protein phosphorylated at a threonine residue at position 181 (τP-181) and total tau protein (τT) constitute the three established (classical) biomarkers for Alzheimer’s disease (AD) [1].