MAPT and early-onset autosomal dominant Alzheimer disease: Hippocampal atrophy is a hallmark of Alzheimer’s disease that ranges on a continuum from healthy aging to mNCD and dementia, similar to other biomarkers of disease pathology (e.g., cerebrospinal fluid biomarkers such as the Aβ42 level, tau, or p-tau) or cognitive performance, with high prognostic value for disease progression [3–6].