Cerebrospinal fluid (CSF) biomarkers for amyloid-β (Aβ42), total tau (T-tau), and phosphorylated tau (P-tau) work well to identify certain neurodegenerative disorders such as Alzheimer’s disease (AD) and its underlying pathology1 and are central to the biological definition of the disease2. Here, MAPT is linked to early-onset autosomal dominant Alzheimer disease.