Diagnosis of AD onset during the patient’s lifetime is said to be “possible” or “probable.” Amyloid β42 (Aβ42), total Tau (T-Tau), and phosphorylated Tau proteins (P-Tau) assay in cerebrospinal fluid (CSF) is recommended to increase the level of diagnostic certainty for AD in atypical clinical phenotypes, for inclusion of patients in clinical trials and to improve AD diagnosis at the earliest stages of the disease (1–5). The gene discussed is MAPT; the disease is Alzheimer disease.