PHF1 and Alzheimer disease: We, therefore, compared the immunoreactivity of phospho-tau S396 (pTau S396, PHF-1), a widely used antibody to study Tau pathology in AD, in DS and control organoids at 12 weeks (Citron et al., 1994; Foidl and Humpel, 2018; Aragao Gomes et al., 2021).