APP and early-onset autosomal dominant Alzheimer disease: Over the course of the last 20 years, cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD), including amyloid beta peptide with 42 amino acids (Aβ<sub>42</sub>), total tau protein (τ<sub>T</sub>), and tau protein phosphorylated at a threonine residue at position 181 (τ<sub>P-181</sub>), have become a useful tool for the recognition and diagnosis of AD, even in early or atypical clinical presentations and in the presymptomatic stage of the disease [...].