Semantic dementia arises from focal degeneration of the anterior temporal lobes. The molecular pathology is heterogeneous. In sporadic cases, TDP-43 proteinopathy (FTLD-TDP type C) is the most frequently identified underlying neuropathological substrate. Familial forms have been associated with pathogenic variants in MAPT (microtubule-associated protein tau, chromosome 17) and PSEN1 (presenilin-1, chromosome 14). MAPT mutations are more broadly associated with a range of FTD phenotypes including behavioral variant FTD and parkinsonian syndromes; the GeneReviews chapter on MAPT-related FTD documents that different MAPT variants produce distinct genotype-phenotype correlations across clinical presentations. PSEN1 variants are more commonly associated with familial Alzheimer's disease but have been identified in atypical FTD-spectrum phenotypes. Familial cases of semantic dementia show autosomal dominant inheritance. The majority of cases, however, are sporadic, arising without a clear hereditary basis, and the molecular trigger initiating TDP-43 aggregation in sporadic disease remains under investigation.

Diagnosis rests on clinical criteria requiring documentation of core semantic deficits. International consensus criteria for semantic variant PPA (Gorno-Tempini et al., 2011) specify single-word comprehension impairment and confrontation naming difficulty as primary features, alongside supportive findings of impaired object knowledge and surface dyslexia or dysgraphia. Neuroimaging plays a central role: MRI demonstrates asymmetric anterior temporal lobe atrophy, and FDG-PET reveals hypometabolism in the same regions. Neuropsychological testing quantifies the degree and profile of semantic memory impairment across verbal and nonverbal domains. When familial history is present, molecular genetic testing for MAPT and GRN (granulin precursor) variants is informative; GRN mutations are the most frequent identified cause of svPPA in familial series. Cerebrospinal fluid biomarkers and tau PET imaging are used in specialized centers to characterize underlying proteinopathy. The GeneReviews chapter on MAPT-related FTD describes comprehensive diagnostic evaluation encompassing neurological examination, behavioral assessment, and cognitive testing.

No disease-modifying therapy has received regulatory approval for semantic dementia. Current management is entirely supportive and multidisciplinary. According to GeneReviews, management of frontotemporal dementia manifestations commonly encompasses speech-language pathology addressing communication deficits, physical therapy supporting mobility and strength, occupational therapy facilitating functional adaptation, and psychological or psychiatric support for behavioral symptoms. Communication aids and memory books can extend functional communication in individuals with progressive anomia. Pharmacological interventions are symptom-directed; antidepressants and antipsychotics are used off-label to manage behavioral disturbances in appropriate clinical contexts. One orphan drug designation within the broader FTD category is relevant to the biological context of semantic dementia: a recombinant AAV9 vector encoding the human progranulin gene (PGRN; sponsor: AviadoBio Ltd.) has received orphan designation for frontotemporal dementia. This agent is investigational and has not received marketing approval.

Semantic dementia follows a relentlessly progressive course without remission. Semantic deficits deepen over time, extending from initial word and object knowledge impairment to broader loss across all modalities of recognition and conceptual knowledge. Behavioral symptoms typically emerge or intensify in later stages, particularly as right temporal involvement increases. The rate of progression varies across individuals. The broader FTD population typically survives approximately six to eight years from symptom onset, though the range is wide and varies by underlying pathology and individual factors. Specific survival data for semantic dementia as a distinct entity are limited. As the disease advances, functional dependence increases across activities of daily living and communication. The GeneReviews chapter on MAPT-related FTD notes that penetrance of pathogenic MAPT variants is high, with most pathogenic variant carriers developing clinical disease by a disease-specific age of onset.

Several clinical studies are active within the semantic dementia and svPPA research landscape. The Veri-T trial (NCT05184569) is evaluating verdiperstat specifically in participants with svPPA attributable to TDP-43 pathology. Investigations of non-invasive neuromodulation approaches in primary progressive aphasia (NCT07260253) are recruiting. Additional studies include biomarker surveillance programs (NCT04516499) examining neurofilament levels and other markers across the FTD spectrum, as well as comprehensive natural history studies spanning FTD and ALS-related phenotypes (NCT03225144). Investigational therapeutic strategies described in GeneReviews for MAPT-related FTD include gene therapy approaches and disease-modifying interventions targeting tau and neuroinflammatory pathways. Progranulin restoration strategies, antisense oligonucleotides targeting C9orf72, and tau-directed immunotherapies represent active areas of research within the broader FTD field, with relevance to distinct molecular subtypes of semantic dementia depending on neuropathological substrate.