Semantic dementia is a neurodegenerative disorder characterized by the loss of semantics, or the meaning of nouns and objects. It is one of three major fronto-temporal degenerations, which have their usual onset in the presenium. Although these syndromes are pathologically heterogeneous, most patients with semantic dementia have anterior temporal pathology with abnormal intraneu-ronal ubiquitin-positive inclusions containing deposits of misfolded transactive response DNA-binding protein 43 (TDP-43). Clinically, the earliest and most common deficit in semantic dementia is semantic anomia, or language difficulty characterized by the loss of meaning of words. The deficits in semantic dementia, however, extend beyond language to involve a multimodal or "amodal" impairment in the knowledge of objects, faces, smells, other perceptions, or concepts.
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