Together the combined analysis of CSF total tau and Aβ1–42 levels provides the most sensitive and specific laboratory-based test for AD and MCI (Andreasen et al. 2001; Hulstaert et al. 1999) that in conjunction with neuro-imaging and a detailed case history could be effectively implemented in the clinic and to date provides the gold standard to which all other tests for putative molecular biomarkers of AD should be compared. This evidence concerns the gene MAPT and Alzheimer disease.