MAPT and Alzheimer disease: More recently, the so-called AT(N) system (A for amyloid load, T for tau accumulation and N for neurodegeneration) [40] has been proposed by the National Institute of Aging and Alzheimer’s Association (NIA–AA) Research Framework group, in which AD is viewed as a biological process, irrespective of the type (amnestic vs non-amnestic presentations), severity (MCI vs dementia) or even absence of symptoms (pre-clinical stage) at a certain time point [41].