Heterogeneous group of neurodegenerative disorders characterized by frontal and temporal lobe atrophy associated with neuronal loss, gliosis, and dementia. patients exhibit progressive changes in social, behavioral, and/or language function. Multiple subtypes or forms are recognized based on presence or absence of TAU PROTEIN inclusions. FTLD includes three clinical syndromes: frontotemporal dementia, semantic dementia, and primary progressive nonfluent aphasia.