MAPT and argyrophilic grain disease: While this unifying disease mechanism is the underlying cause of several frontotemporal lobar degenerative diseases (FTLDs), including argyrophilic grain disease (AGD), corticobasal degeneration (CBD), globular glial tauopathy (GGT), and progressive supranuclear palsy (PSP), each disease is defined by a unique clinical presentation, as well as type and distribution of tau inclusions in the brain.