Primary progressive aphasia (PPA) is an uncommon neurodegenerative syndrome characterized by progressive deterioration of language function as the dominant initial clinical feature. Estimated prevalence is 1 to 9 per 100,000 individuals, placing it in the uncommon category. The condition represents one of the frontotemporal dementia spectrum disorders, arising from neurodegeneration affecting the frontal and temporal cortex. Documented subtypes in this packet include GRN-related frontotemporal lobar degeneration with TDP-43 inclusions and logopenic progressive aphasia. GeneReviews characterization of GRN frontotemporal dementia — a disorder in which primary progressive aphasia is an established clinical presentation — indicates that frontotemporal dementia overall accounts for 5% to 10% of individuals with dementia and 10% to 20% of those with dementia onset before age 65. GRN-related frontotemporal dementia represents approximately 5% of all frontotemporal dementia cases and approximately 20% of cases with a positive family history. The GRN-related form typically manifests in the sixth to eighth decade, with age of onset ranging from 35 to 87 years and a mean of approximately 64.9 years in documented series.

The hallmark feature of primary progressive aphasia is progressive language dysfunction. In the GRN-related frontotemporal dementia presentations that include primary progressive aphasia, affected individuals may also experience behavioral variant frontotemporal dementia features, atypical parkinsonism, or corticobasal syndrome, reflecting the broad clinical spectrum of GRN-FTD. GeneReviews clinical description indicates that GRN-FTD primarily affects the frontal and temporal cortex, with additional involvement of the parietal cortex and basal ganglia producing parkinsonism, cortical basal syndrome, and memory impairment in some individuals. Language disturbances include decline in naming, verbal fluency, and language production, with specific patterns dependent on the clinical variant. Behavioral changes that may co-occur include early disinhibition, loss of social conventions, impulsivity, and compulsive behaviors. Apathy and impaired executive function are documented features. GeneReviews notes that behavioral changes and loss of insight and judgment can represent a considerable burden for caregivers. The logopenic progressive aphasia subtype documented in this packet is distinguished by specific phonological and word retrieval deficits. Clinical variability in the GRN-related form is high, even among individuals sharing the same pathogenic variant.

Primary progressive aphasia arises from neurodegeneration affecting language-dominant cortical networks. Specific gene names are not provided in this packet's verified known_genes field. GeneReviews characterization of GRN-related frontotemporal dementia describes pathogenic variants affecting the progranulin gene as the basis for one hereditary form, with inheritance following an autosomal dominant pattern. Penetrance in the GRN-related form is estimated at approximately 90% by age 75 years, though apparent reduced penetrance has been observed. A study of a common pathogenic variant found that 60% of carriers were affected by age 60 years, and more than 95% by age 70. No obvious genotype-phenotype correlations between specific pathogenic variants and clinical presentation have been identified; variability is high among individuals carrying the same variant. GRN-related frontotemporal dementia accounts for approximately 3.2% of simplex cases in large series. Other forms of primary progressive aphasia — including the logopenic subtype documented in this packet — arise through distinct neuropathological mechanisms not described in this packet's verified data.

Diagnostic evaluation of primary progressive aphasia encompasses clinical assessment, neuroimaging, neuropsychological testing, and in appropriate cases molecular genetic testing. GRN frontotemporal dementia is suspected in individuals presenting with clinical features including behavioral variant frontotemporal dementia, primary progressive aphasia, atypical parkinsonism, or corticobasal syndrome. Neuroimaging evaluates for alternative structural etiologies including white matter disease, frontotemporal focal lesions, frontal lobe tumors, and cerebrovascular disease. Neuropsychological assessment provides comprehensive and objective characterization of language and cognitive function when clinical evaluations are insufficient. Molecular genetic testing is relevant when a familial pattern consistent with autosomal dominant inheritance is identified. Detailed general, neurologic, and family history alongside physical and neurologic examination form the foundation of initial evaluation. Clinical manifestations of GRN-related frontotemporal dementia overlap significantly with those of other conditions including FTD associated with MAPT pathogenic variants, Parkinson disease, Alzheimer disease, Pick disease, corticobasal degeneration, and progressive supranuclear palsy, all of which fall within the differential diagnosis.

No approved pharmacologic treatments are listed in this packet's foundational therapies or approved treatments fields for primary progressive aphasia. GeneReviews explicitly notes that no known treatment exists for GRN-related frontotemporal dementia or for frontotemporal dementia broadly. Psychosocial support is central to management, encompassing occupational therapy, environmental adaptations, and physical interventions. GeneReviews documents that certain behavioral manifestations including apathy, impulsivity, and compulsiveness may show a clinical response to selective serotonin reuptake inhibitors. Psychological support for partners and other caregivers is part of comprehensive management, given the behavioral changes and loss of insight and judgment associated with frontotemporal dementia presentations. Individuals are typically followed in memory disorder clinics or multidisciplinary settings involving neurologic and psychiatric services, as noted in the GeneReviews surveillance section. Multiple clinical trials are actively investigating therapeutic approaches in primary progressive aphasia and related frontotemporal syndromes.

Primary progressive aphasia follows a progressive neurodegenerative course. In GRN-related frontotemporal dementia, GeneReviews data from large study series indicates a median age at onset of 58 years in individuals with GRN pathogenic variants, compared to 61 years in those without. Median age at death was 65.5 years in GRN-related cases versus 69 years in non-GRN cases in the same series. Penetrance by age 75 years is estimated at approximately 90% in GRN pathogenic variant carriers. Clinical variability is high among individuals carrying the same pathogenic variant, and significant intrafamilial variability is well-documented. Natural history data specific to primary progressive aphasia across all clinical subtypes are not available in this packet beyond the GRN-FTD characterization in GeneReviews. Long-term follow-up in memory disorder clinics and multidisciplinary care settings is the described standard of care trajectory.

Multiple clinical trials in primary progressive aphasia and related frontotemporal dementia syndromes are documented in this packet. Studies include an interventional investigation of transcranial direct current stimulation targeting language and executive control networks in the logopenic variant of primary progressive aphasia (NCT03887481, Johns Hopkins University, recruiting). Additional trials are investigating remotely administered interventions and other therapeutic modalities. GeneReviews notes that clinical trial resources including ClinicalTrials.gov and the EU Clinical Trials Register provide access to ongoing studies for frontotemporal dementia spectrum disorders. Therapeutic development in progranulin-related frontotemporal dementia represents an active research domain, with investigational strategies targeting disease-modifying approaches under evaluation.