MAPT and Alzheimer disease: This fact has currently initiated another hot debate on the proposed biological definition of AD (based on protein changes in amyloid and tau) called the recently revised AT(N)-system with A for amyloid, T for tau (and N for neurodegeneration) as justification (Høilund-Carlsen et al., 2024b; Lista et al., 2024; Jack et al., 2024).