In the case of tau protein, the involvement of several protein isoforms in patients’ fibrils (either by a combination of the 3R/4R isoforms, as in AD, or exclusively 3R, as in Pick’s disease, or 4R isoforms, as in corticobasal degeneration) is in part responsible of distinct folds of tau in tauopathies. This evidence concerns the gene MAPT and Alzheimer disease.