Cerebrospinal fluid (CSF) tests for amyloid-β (Aβ42 or Aβ42/40 ratio), phosphorylated tau (p-tau), and total tau (t-tau) have been incorporated into the biological definition of Alzheimer’s disease proposed by the National Institute of Aging and the Alzheimer’s Association (NIA-AA) [3]. This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.