MAPT and Alzheimer disease: Our study provides proof-of-concept evidence that in the case of Aβ and tau discordance (Aβ(+)T(-)), cognitive decline could be associated with changes within the AD spectrum in a multi-morbidity context, i.e., mixed AD, while in the case of Aβ and tau positivity concordance (Aβ(+)T(+)), AD pathology is the main contributor to cognitive decline.