The measurements of Aβ1-42 (Aβ42), total tau (tTau), and phosphorylated tau at Thr181 (pTau181) in cerebrospinal fluid (CSF), as well as the visualization of fibrillar Aβ protein loads in the brain using a radioactive ligand, have proven useful in the early diagnosis of AD, which leads to their inclusion in diagnostic guidelines2,3 and biological definitions of AD4. The gene discussed is MAPT; the disease is Alzheimer disease.