A most successful biomarker-based method of predicting the conversion from MCI to AD has been the analysis of cerebrospinal fluid (CSF) and in particular total tau (tau), tau phosphorylated at Thr181 (P-tau) and the 42-amino-acid isoform of amyloid-β1–42 (Aβ42). This evidence concerns the gene MAPT and Alzheimer disease.