An example of a successful biomarker of conversion from MCI to AD is the analysis of proteins present in the cerebrospinal fluid (CSF) and in particular total tau (tau), phosphorylated tau (P-tau), and the 42-amino-acid isoform of amyloid-β1–42 (Aβ42) (Parnetti et al., 2012). This evidence concerns the gene MAPT and Alzheimer disease.