Fluid biomarkers for Alzheimer’s disease (AD) in CSF and blood including different forms of β-amyloid and phosphorylated tau make such an approach possible in AD (Zetterberg and Blennow, 2018), although even these are indirect measures for the proteopathic seeds that are assumed to be driving neurodegeneration. The gene discussed is MAPT; the disease is early-onset autosomal dominant Alzheimer disease.