Tau fibrils assembled from the co-incubation of the MTBD of tau and polyanions such as heparin, have been widely used to study tau’s propensity to seed wild-type (WT) and mutant tau in vitro and in vivo (Guo and Lee, 2011; Iba et al., 2013; Chakrabarty et al., 2015; Strang et al., 2018; Xia et al., 2021), but heparin-induced tau fibrils do not completely recapitulate filaments found in the brains of patients with tauopathies (Zhang et al., 2019). This evidence concerns the gene MAPT and tauopathy.