MAPT and early-onset autosomal dominant Alzheimer disease: When measured in CSF, a combination of decreased concentrations of Aβ42 and increased concentrations of p-Tau and total tau (t-Tau) are consistent with Alzheimer disease.3 Cerebrospinal fluid biomarkers offer greater accessibility and lower costs than amyloid positron emission tomography and may play a pivotal role in qualifying patients for new US Food and Drug Administration–approved treatments that slow disease progression.