The recent ATN diagnostic classification of AD incorporates these biomarkers: amyloid (detected using CSF or PET examinations), tau (also by CSF or PET), and neuronal loss (medial temporal lobe and hippocampal atrophy on MR imaging) defines AD, even in its preclinical stage without brain atrophy and cognitive symptoms (i.e., A+T+N−) [23]. The gene discussed is MAPT; the disease is Brain atrophy.