MAPT and Alzheimer disease: However, competition studies showed that it has a relatively low affinity for recombinant tau fibrils (Ki 59.3 nM) and even lower for PHF in AD brain homogenates (Kd 86.5 nM) than synthetic heparin-induced tau polymers (HITP) Kd 1.67 nM (Table 2), an evidence of the inadequacies of synthetic tau preparations, which fails to completely replicate native tau aggregates in vivo [156,157].