If true, it is unclear why a therapeutic effect was absent in an earlier phase of AD, but it could be hypothesized that different species of tau more amenable to semorinemab engagement predominate in later stages of the disease; there may be higher concentrations of N-terminal tau fragments in later-stage disease if they are related to the overall amount of cortical tau pathology (soluble or insoluble). Here, MAPT is linked to Alzheimer disease.