Indeed, results from several groups demonstrated that normalization of the CSF Aβ42 concentration to the level of total Aβ peptides, using the Aβ42/40 ratio, improved the distinction between dementia and controls [22, 23] and also between AD and non-AD dementia [24–26], particularly in cases with ambiguous core CSF biomarker profiles (i.e., isolated reduction of Aβ42 or elevation of t-Tau/p-Tau) [27–29]. The gene discussed is MAPT; the disease is Alzheimer disease.