An assay that selectively binds to brain-derived tau (BD-tau) while avoiding tau from peripheral sources has been investigated for its diagnostic potential in Alzheimer's disease.67 BD-tau in serum significantly correlated with paired CSF BD-tau and was able to differentiate Alzheimer's disease from healthy controls with mean levels of 32.4 pg/mL compared with 3.6 pg/mL. Here, MAPT is linked to early-onset autosomal dominant Alzheimer disease.