In this study, we examined sarkosyl-insoluble and trypsin-resistant fragments of abnormal tau from brains of patients with AD, PiD, CBD, PSP, and intronic MAPT mutations, and found that the core units of the tau aggregates were composed of different tau repeat regions located between residues 243–406, indicating that the conformations of the aggregates are disease-specific. The gene discussed is MAPT; the disease is Alzheimer disease.