Soluble C-terminally truncated tau species are also preferentially secreted from synaptosomes of Alzheimer’s disease brains (Sokolow et al., 2015) and in conditioned media from patient-derived induced pluripotent stem cell cortical neurons (Bright et al., 2015; Kanmert et al., 2015; Sato et al., 2018). Here, MAPT is linked to early-onset autosomal dominant Alzheimer disease.