Disease Pathophysiology Research Report

Target Disease

Disease Name: Primary Progressive Aphasia (PPA)
MONDO ID: not specified in source set
Category: Neurodegenerative disease

Overview and key concepts

Primary progressive aphasia (PPA) is a language-led neurodegenerative syndrome with three canonical clinical variants: semantic variant (svPPA), nonfluent/agrammatic variant (nfvPPA; also agPPA), and logopenic variant (lvPPA). Clinicopathological correlation shows probabilistic links to molecular proteinopathies: svPPA most often to FTLD-TDP (type C), nfvPPA to primary tauopathies (commonly 4-repeat tau in PSP/CBD; less often 3R tau/Pick disease), and lvPPA to Alzheimer’s disease (AD; Aβ/tau) pathology. Large autopsy-linked cohorts and refined imaging-based classification approaches published in 2023–2024 consolidate these associations and map distinct network-based epicenters of degeneration across variants (e.g., anterior temporal pole in svPPA; left posterior inferior frontal/insula network in nfvPPA; left temporo-parietal network in lvPPA) (URL: https://doi.org/10.1136/jnnp-2023-332862, Mar 2024; https://doi.org/10.1212/WNL.0000000000209924, Nov 2024; https://doi.org/10.1007/s12149-024-01958-w, Jul 2024) (shir2024clinicoradiologicalandneuropathological pages 1-2, watanabe2024primaryprogressiveaphasia pages 1-2, mirbod2024fdgpetinthe pages 1-2).

1. Core pathophysiology

Variant–proteinopathy correlations: In an autopsy cohort of 82 PPAs (1998–2022), lvPPA corresponded to AD in ~80%, agPPA/nfvPPA to tauopathies in ~89%, and svPPA to FTLD-TDP in ~72%. The presence of apraxia of speech in agPPA predicted 4R tau (PSP/CBD) while “pure” agrammatism without apraxia enriched for 3R tau (Pick disease), providing a clinical marker for tau isoform pathology (URL: https://doi.org/10.1136/jnnp-2023-332862, 2024) (shir2024clinicoradiologicalandneuropathological pages 1-2, shir2024clinicoradiologicalandneuropathological pages 8-10, shir2024clinicoradiologicalandneuropathological pages 4-6).
Network-based neurodegeneration: FDG-PET and MRI demonstrate variant-specific hypometabolism/atrophy in the left language network: anterior temporal lobe in svPPA, left inferior frontal gyrus/insula in nfvPPA, and left temporo-parietal junction in lvPPA. Data-driven PET decomposition and machine-learning can predict underlying pathology with balanced accuracy ~76% (URL: https://doi.org/10.1007/s12149-024-01958-w, 2024; https://doi.org/10.1136/jnnp-2023-332862, 2024) (mirbod2024fdgpetinthe pages 1-2, shir2024clinicoradiologicalandneuropathological pages 4-6, shir2024clinicoradiologicalandneuropathological pages 10-11).
Glial/lysosomal mechanisms (GRN-related FTLD): Progranulin (PGRN) haploinsufficiency (GRN LOF) causes lysosomal dysfunction, lipid storage (lipofuscin), and neuroinflammation; patient-derived microglia show cytoplasmic TDP-43 aggregation and lysosomal abnormalities with complement C1q activation and impaired phagocytosis (URL: https://doi.org/10.1186/s12974-024-03039-1, Feb 2024) (sung2024progranulinhaploinsufficiencymediates pages 1-2). Biofluid and tissue studies in genetic and sporadic FTD support elevations of lysosomal metabolites (e.g., glucosylsphingosine) and glial markers (GFAP, YKL-40), and neuronal injury (NfL), consistent with lysosomal-glial pathobiology (URL: https://doi.org/10.1101/2024.02.09.579529, Feb 2024) (hsiaonakamoto2024alterationsinlysosomal pages 1-5, hsiaonakamoto2024alterationsinlysosomal pages 27-30).
Progression beyond language networks: Baseline atrophy in control/salience/default and ventral frontotemporal networks predicts earlier transition to dementia in PPA, underscoring spread beyond core language nodes in prognosis (URL: https://doi.org/10.1212/WNL.0000000000201403, Jan 2023) (tetzloff2023amyloidandtau pages 1-3).

2. Key molecular players

Genes/proteins (HGNC):
GRN (HGNC:4601; progranulin): haploinsufficiency → lysosomal dysfunction, microglial activation, TDP-43 pathology; biomarker/therapeutic target (AAV9 PR006) (sevigny2024progranulinaavgene pages 1-2, sung2024progranulinhaploinsufficiencymediates pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 1-5).
MAPT (HGNC:6893; tau): 3R vs 4R tauopathy differentially linked to agPPA sub-phenotypes (apraxia predictor) (shir2024clinicoradiologicalandneuropathological pages 8-10, shir2024clinicoradiologicalandneuropathological pages 4-6, shir2024clinicoradiologicalandneuropathological pages 1-2).
TARDBP (HGNC:11586; TDP-43): svPPA most often FTLD-TDP type C; TDP-43 aggregates also observed in GRN-deficient microglia in vitro (shir2024clinicoradiologicalandneuropathological pages 1-2, sung2024progranulinhaploinsufficiencymediates pages 1-2).
C9orf72 (HGNC:30055): FTLD spectrum gene; contributes to TDP-43 proteinopathy risk and biomarker heterogeneity in FTD cohorts with PPA presentations (hsiaonakamoto2024alterationsinlysosomal pages 1-5).
AD-related: APP/PSENs/Aβ/tau axis implicated in lvPPA given high amyloid/tau positivity and AD neuropathology (watanabe2024primaryprogressiveaphasia pages 1-2, mirbod2024fdgpetinthe pages 1-2).
Chemical entities (CHEBI; where applicable):
2-deoxy-2-[18F]fluoro-D-glucose (FDG; CHEBI:36932) for FDG-PET hypometabolism mapping (mirbod2024fdgpetinthe pages 1-2).
Glucosylsphingosine (lyso-Gb1; lysosomal biomarker elevated in GRN-FTD plasma/tissue) (hsiaonakamoto2024alterationsinlysosomal pages 1-5, hsiaonakamoto2024alterationsinlysosomal pages 27-30).
Cell types (CL): neurons, microglia (CL:0000129), astrocytes (CL:0000127), oligodendrocytes (CL:0000128). Microglial activation and astroglial reactivity (GFAP, YKL-40) are prominent in GRN-related disease; neuronal/oligodendroglial tau may dominate PET signal in primary tauopathies (URL: https://doi.org/10.1007/s00401-024-02834-7, Nov 2024) (sevigny2024progranulinaavgene pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 1-5, hsiaonakamoto2024alterationsinlysosomal pages 27-30).
Anatomical locations (UBERON): left anterior temporal lobe/pole (svPPA), left inferior frontal gyrus and insula (nfvPPA), left temporo-parietal junction and superior temporal regions (lvPPA) (mirbod2024fdgpetinthe pages 1-2, shir2024clinicoradiologicalandneuropathological pages 1-2, watanabe2024primaryprogressiveaphasia pages 1-2).

3. Biological processes (candidate GO terms)

Protein aggregation and proteostasis: TDP-43 aggregation (svPPA; GRN-related microglia/neurons), tau aggregation (nfvPPA; 3R/4R isoform–specific) (shir2024clinicoradiologicalandneuropathological pages 1-2, sung2024progranulinhaploinsufficiencymediates pages 1-2).
Lysosomal organization and catabolism; lipid metabolism and storage (lipofuscin; gangliosides); autophagy-lysosome pathway dysfunction (GRN-FTD) (sevigny2024progranulinaavgene pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 1-5, hsiaonakamoto2024alterationsinlysosomal pages 27-30).
Innate immune activation and complement signaling (C1q); microglial phagocytosis and synaptic pruning abnormalities (GRN LOF) (sung2024progranulinhaploinsufficiencymediates pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 38-41).
Synaptic dysfunction and neurodegeneration markers (NPTXR/NPTX1/2, VGF decreased in CSF; NfL increased) (hsiaonakamoto2024alterationsinlysosomal pages 1-5).
Network degeneration: hypometabolism/atrophy across language and control/salience/default networks relates to clinical progression (tetzloff2023amyloidandtau pages 1-3, mirbod2024fdgpetinthe pages 1-2).

4. Cellular components

Lysosome and late endosome compartments in microglia/neurons (GRN-related dysfunction; lipofuscin accumulation) (sevigny2024progranulinaavgene pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 1-5).
Cytoplasm (TDP-43 mislocalization/aggregation in microglia; neuronal cytoplasmic inclusions) (sung2024progranulinhaploinsufficiencymediates pages 1-2).
Synapses (altered pruning and synaptic protein biomarkers in FTD) (hsiaonakamoto2024alterationsinlysosomal pages 1-5).
Myelin/white matter tracts affected in nfvPPA network degeneration; oligodendroglial tau contributes to PET signal in 4R tauopathies (URL: https://doi.org/10.1007/s00401-024-02834-7, 2024) (mirbod2024fdgpetinthe pages 1-2, sevigny2024progranulinaavgene pages 1-2).

5. Disease progression

Sequence and staging: “Epicenter” degeneration with network spread. svPPA begins in anterior temporal pole with progressive semantic degradation; nfvPPA begins in left posterior inferior frontal/insula–premotor network leading to agrammatism and/or apraxia of speech; lvPPA begins in left posterior temporal/inferior parietal regions with phonologic working-memory deficits (URL: https://doi.org/10.1007/s12149-024-01958-w, 2024; https://doi.org/10.1136/jnnp-2023-332862, 2024) (mirbod2024fdgpetinthe pages 1-2, shir2024clinicoradiologicalandneuropathological pages 1-2).
Phenotypic evolution: agPPA frequently evolves into corticobasal or PSP syndromes (~64%); svPPA evolves to bvFTD (~44%); lvPPA often remains language-predominant within AD spectrum (URL: https://doi.org/10.1136/jnnp-2023-332862, 2024) (shir2024clinicoradiologicalandneuropathological pages 1-2).
Prognosis from network burden: baseline atrophy in non-language networks (frontoparietal control and ventral frontotemporal) predicts earlier dementia conversion, independent of language network burden (URL: https://doi.org/10.1212/WNL.0000000000201403, 2023) (tetzloff2023amyloidandtau pages 1-3).

6. Phenotypic manifestations (HP terms/examples)

Aphasia (HP:0002381) with variant-specific features: anomia and semantic loss (svPPA), agrammatism/dysprosody/apraxia of speech (nfvPPA; HP:0031542), impaired sentence repetition/phonologic errors and word-finding pauses (lvPPA) (watanabe2024primaryprogressiveaphasia pages 1-2, mirbod2024fdgpetinthe pages 1-2).
Additional features: nonverbal oral apraxia and spread to motor networks in nfvPPA spectrum; behavioral changes as svPPA spreads to right ATL/bvFTD phenotype (recent clinicopathology and imaging) (shir2024clinicoradiologicalandneuropathological pages 1-2, mirbod2024fdgpetinthe pages 1-2).

Recent developments and latest research (2023–2024 prioritized)

Clinicoradiological–neuropathological refinement: A 2024 autopsy series linked apraxia of speech to 4R tau and “pure” agrammatism to 3R tau, improving in vivo prediction of tau isoform pathology. PET machine-learning decomposition improved prediction of underlying proteinopathy; “lvPPA-AD” showed characteristic superior temporal sulcus involvement (URL: https://doi.org/10.1136/jnnp-2023-332862, 2024) (shir2024clinicoradiologicalandneuropathological pages 8-10, shir2024clinicoradiologicalandneuropathological pages 4-6, shir2024clinicoradiologicalandneuropathological pages 10-11).
FDG-PET systematic review (2024): Distinct hypometabolic signatures across PPA variants were consolidated: ATL in svPPA, IFG/insula in nfvPPA, temporoparietal junction in lvPPA; authors recommend integration with other modalities for specificity (URL: https://doi.org/10.1007/s12149-024-01958-w, 2024) (mirbod2024fdgpetinthe pages 1-2).
lvPPA re-conceptualization as AD-related aphasia spectrum (2024): Repetition impairment mapped to left superior temporal hypometabolism; subgroups (pure-LPA, Wernicke-like, anomic-like, TCSA-like) showed predominant AD neuropathology (70% overall; 100% in repetition-impaired subgroups) (URL: https://doi.org/10.1212/WNL.0000000000209924, 2024) (watanabe2024primaryprogressiveaphasia pages 1-2).
AOS/PAA and AD biomarkers (Dec 2023): About half of AOS-PAA patients were positive on Aβ and/or tau PET, yet clinical phenotype did not track AD biomarkers, indicating that 4R tauopathy often underlies these syndromes despite AD co-pathology on PET (URL: https://doi.org/10.3233/JAD-230912, 2023) (tetzloff2023amyloidandtau pages 1-3).
GRN mechanistic and therapeutic advances (2024):
Human microglia from GRN carriers showed cytoplasmic TDP-43 aggregation, lipid droplets, and lysosomal defects driven by complement C1q/inflammation (URL: https://doi.org/10.1186/s12974-024-03039-1, 2024) (sung2024progranulinhaploinsufficiencymediates pages 1-2).
Biomarkers in FTD cohorts: plasma/tissue glucosylsphingosine elevated in GRN carriers; GFAP and CSF YKL-40 elevated in asymptomatic carriers and symptomatic groups; NfL elevated across groups and correlated with severity/progression (preprint) (URL: https://doi.org/10.1101/2024.02.09.579529, 2024) (hsiaonakamoto2024alterationsinlysosomal pages 1-5, hsiaonakamoto2024alterationsinlysosomal pages 27-30).
AAV9 PR006 progranulin gene therapy: First-in-human phase 1/2 interim analysis showed dose-dependent CSF progranulin increases in all patients, acceptable short-term safety (CSF pleocytosis most common AE; transient NfL rises consistent with dorsal root ganglion sensitivity), and nonclinical reversal of lysosomal/inflammatory phenotypes in Grn-/- models (URL: https://doi.org/10.1038/s41591-024-02973-0, May 2024) (sevigny2024progranulinaavgene pages 1-2).

Current applications and real-world implementations

Imaging-based diagnosis and prognostication: FDG-PET patterns and MRI atrophy maps support variant classification in clinical practice; amyloid PET strongly supports lvPPA→AD linkage, and tau PET can aid differential diagnosis in suspected primary tauopathies, though clinical context and autopsy series caution about co-pathology and sensitivity limits (URL: https://doi.org/10.1007/s12149-024-01958-w, 2024; https://doi.org/10.3233/JAD-230912, 2023) (mirbod2024fdgpetinthe pages 1-2, tetzloff2023amyloidandtau pages 1-3).
Machine-learning PET decomposition: Data-driven FDG-PET pipelines applied to PPA cohorts can predict underlying pathology, supporting trial stratification and counseling (URL: https://doi.org/10.1136/jnnp-2023-332862, 2024) (shir2024clinicoradiologicalandneuropathological pages 4-6, shir2024clinicoradiologicalandneuropathological pages 10-11).
Biomarker panels in FTD/GRN context: Plasma GFAP/NfL, CSF YKL-40, and lysosomal lipids (glucosylsphingosine) are emerging biomarkers for screening and progression monitoring in genetic FTD programs that include PPA phenotypes (URL: https://doi.org/10.1101/2024.02.09.579529, 2024) (hsiaonakamoto2024alterationsinlysosomal pages 1-5, hsiaonakamoto2024alterationsinlysosomal pages 27-30).
Gene therapy for GRN-FTD: PR006 (intracisternal AAV9-GRN) increased CSF progranulin in all treated participants in phase 1/2 interim analysis; continued follow-up is ongoing to assess efficacy (URL: https://doi.org/10.1038/s41591-024-02973-0, 2024) (sevigny2024progranulinaavgene pages 1-2).

Expert opinions and authoritative analysis

“LvPPA is overwhelmingly an Alzheimer’s-spectrum aphasia,” with amyloid positivity defining an AD-related aphasia spectrum and repetition impairment mapping to left superior temporal hypometabolism; specifying moderate/severe repetition deficits as a core lvPPA feature may reduce pathologic heterogeneity (Neurology, 2024) (watanabe2024primaryprogressiveaphasia pages 1-2).
“Apraxia of speech is a clinicopathologic marker of 4R tauopathy (PSP/CBD) in agPPA,” whereas “pure” agrammatism without apraxia enriches for 3R tau (Pick disease), enabling in vivo stratification relevant to tau-targeted trials (JNNP, 2024) (shir2024clinicoradiologicalandneuropathological pages 8-10, shir2024clinicoradiologicalandneuropathological pages 1-2).
FDG-PET is emphasized as diagnostically useful across variants but should be integrated with amyloid/tau PET and structural imaging due to overlapping patterns and co-pathology in atypical cases (Ann Nucl Med, 2024) (mirbod2024fdgpetinthe pages 1-2).

Relevant statistics and data from recent studies

Autopsy-confirmed variant–pathology proportions (n=82 PPA): lvPPA ~80% AD; agPPA ~89% tauopathy; svPPA ~72% FTLD-TDP; overall pathology distribution: FTLD-tau 38%, AD 35%, FTLD-TDP 21%, LBD 6% (JNNP, 2024) (shir2024clinicoradiologicalandneuropathological pages 8-10).
agPPA stratification by apraxia: apraxia of speech → 86% 4R tau (PSP/CBD); “pure” agrammatism → 67% 3R tau (PiD) (JNNP, 2024) (shir2024clinicoradiologicalandneuropathological pages 8-10).
FDG-PET machine-learning prediction: balanced accuracy 75.6% (sensitivity 83.3%, specificity 92.6%) for primary pathology prediction in PPA (JNNP, 2024) (shir2024clinicoradiologicalandneuropathological pages 4-6).
lvPPA/language-AD spectrum: 70% AD pathology overall in a PPA cohort lacking nfv/sv core features; repetition-impaired subgroups uniformly AD (Neurology, 2024) (watanabe2024primaryprogressiveaphasia pages 1-2).
Prognostic networks in PPA: Hazard ratios for progression to dementia linked to baseline atrophy in frontoparietal control (HR 1.94) and ventral frontotemporal (HR 1.61) networks (Neurology, 2023) (tetzloff2023amyloidandtau pages 1-3).
GRN biomarkers: Plasma glucosylsphingosine elevated in symptomatic and asymptomatic GRN carriers; plasma GFAP and CSF YKL-40 elevated in asymptomatic carriers and symptomatic groups; NfL correlates with disease severity/progression (bioRxiv, 2024) (hsiaonakamoto2024alterationsinlysosomal pages 1-5, hsiaonakamoto2024alterationsinlysosomal pages 27-30).
GRN AAV gene therapy (PR006): CSF progranulin increased in all treated patients; common AE CSF pleocytosis; transient NfL rise post-treatment; one death deemed unrelated (Nat Med, 2024) (sevigny2024progranulinaavgene pages 1-2).

Variant-specific pathophysiology summaries

svPPA (FTLD-TDP type C predominance): Epicenter in left anterior temporal pole; progressive semantic loss; FTLD-TDP type C on pathology in majority; FDG-PET shows ATL hypometabolism. Mechanistically linked to TDP-43 proteinopathy; microglial and lysosomal pathways implicated in FTLD spectrum (URLs: https://doi.org/10.1136/jnnp-2023-332862; https://doi.org/10.1007/s12149-024-01958-w) (shir2024clinicoradiologicalandneuropathological pages 1-2, mirbod2024fdgpetinthe pages 1-2).
nfvPPA/agPPA (primary tauopathies): Left inferior frontal/insula–premotor network with apraxia of speech and agrammatism; apraxia of speech predicts 4R tau (PSP/CBD), whereas “pure” agrammatism predicts 3R tau (Pick). FDG-PET shows IFG/insula hypometabolism; tau PET utility varies and can be confounded by co-pathology (URLs: https://doi.org/10.1136/jnnp-2023-332862; https://doi.org/10.1007/s12149-024-01958-w; https://doi.org/10.3233/JAD-230912) (shir2024clinicoradiologicalandneuropathological pages 8-10, mirbod2024fdgpetinthe pages 1-2, tetzloff2023amyloidandtau pages 1-3).
lvPPA (AD-related aphasia): Left temporo-parietal network with impaired repetition and phonologic working memory; high amyloid/tau positivity and AD neuropathology; refined subtyping (pure-LPA, Wernicke-like, TCSA-like) maps to severity of repetition/comprehension deficits and left superior temporal hypometabolism (URLs: https://doi.org/10.1212/WNL.0000000000209924; https://doi.org/10.1007/s12149-024-01958-w) (watanabe2024primaryprogressiveaphasia pages 1-2, mirbod2024fdgpetinthe pages 1-2).

Ontology-style annotations for knowledge base integration

Genes/proteins (HGNC): GRN (HGNC:4601), MAPT (HGNC:6893), TARDBP (HGNC:11586), C9orf72 (HGNC:30055); AD axis: APP (HGNC:620), PSEN1 (HGNC:9508), PSEN2 (HGNC:9509) (variant-dependent relevance) (watanabe2024primaryprogressiveaphasia pages 1-2, shir2024clinicoradiologicalandneuropathological pages 1-2, sung2024progranulinhaploinsufficiencymediates pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 1-5).
Biological processes (GO, by name): lysosomal function and lipid degradation; microglial activation and complement C1q-mediated synaptic pruning; protein aggregation (tau, TDP-43); synaptic signaling and degeneration; network-level neurodegeneration (sung2024progranulinhaploinsufficiencymediates pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 1-5, tetzloff2023amyloidandtau pages 1-3, mirbod2024fdgpetinthe pages 1-2).
Cell types (CL): neurons; microglia (activation, phagocytosis, complement); astrocytes (reactivity, GFAP); oligodendrocytes (myelin/4R-tau associations) (sevigny2024progranulinaavgene pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 1-5).
Anatomical locations (UBERON): anterior temporal lobe/pole; inferior frontal gyrus; insula; superior temporal gyrus; temporo-parietal junction; pre-supplementary motor area; salience, default, and frontoparietal control networks (shir2024clinicoradiologicalandneuropathological pages 1-2, mirbod2024fdgpetinthe pages 1-2, tetzloff2023amyloidandtau pages 1-3).
Phenotypes (HP): aphasia, anomia, agrammatism, apraxia of speech, surface dyslexia/dysgraphia (variant-dependent) (watanabe2024primaryprogressiveaphasia pages 1-2, mirbod2024fdgpetinthe pages 1-2, shir2024clinicoradiologicalandneuropathological pages 1-2).
Chemical entities (CHEBI/examples): FDG (CHEBI:36932); glucosylsphingosine (lyso-Gb1; lysosomal metabolite); PET ligands (e.g., PiB, flortaucipir) as imaging agents (mirbod2024fdgpetinthe pages 1-2, hsiaonakamoto2024alterationsinlysosomal pages 1-5, tetzloff2023amyloidandtau pages 1-3).

Evidence items with PMIDs/DOIs and dates (URLs)

Shir et al., 2024 (J Neurol Neurosurg Psychiatry), clinicoradiological and neuropathological evaluation; Mar 2024. URL: https://doi.org/10.1136/jnnp-2023-332862 (shir2024clinicoradiologicalandneuropathological pages 1-2, shir2024clinicoradiologicalandneuropathological pages 8-10, shir2024clinicoradiologicalandneuropathological pages 4-6, shir2024clinicoradiologicalandneuropathological pages 10-11).
Watanabe et al., 2024 (Neurology), lvPPA/language-AD spectrum and refined subtyping; Nov 2024. URL: https://doi.org/10.1212/WNL.0000000000209924 (watanabe2024primaryprogressiveaphasia pages 1-2).
Mirbod et al., 2024 (Ann Nucl Med), FDG-PET systematic review; Jul 2024. URL: https://doi.org/10.1007/s12149-024-01958-w (mirbod2024fdgpetinthe pages 1-2).
Tetzloff et al., 2023 (J Alzheimers Dis), Aβ/tau PET in AOS/PAA; Dec 2023. URL: https://doi.org/10.3233/JAD-230912 (tetzloff2023amyloidandtau pages 1-3).
Katsumi et al., 2023 (Neurology), network atrophy predicting progression to dementia; Jan 2023. URL: https://doi.org/10.1212/WNL.0000000000201403 (tetzloff2023amyloidandtau pages 1-3).
Sung et al., 2024 (J Neuroinflammation), GRN haploinsufficiency in human microglia → TDP-43 aggregation, lysosome defects; Feb 2024. URL: https://doi.org/10.1186/s12974-024-03039-1 (sung2024progranulinhaploinsufficiencymediates pages 1-2).
Hsiao-Nakamoto et al., 2024 (bioRxiv), lysosomal/glial/neuronal biomarkers in FTD incl. GRN; Feb 2024. URL: https://doi.org/10.1101/2024.02.09.579529 (hsiaonakamoto2024alterationsinlysosomal pages 1-5, hsiaonakamoto2024alterationsinlysosomal pages 27-30).
Sevigny et al., 2024 (Nature Medicine), AAV9-GRN (PR006) phase 1/2 interim results; May 2024. URL: https://doi.org/10.1038/s41591-024-02973-0 (sevigny2024progranulinaavgene pages 1-2).

Directly supporting quotes (selected): - “LvPPA… mostly associated with AD (80%)… agPPA… 89% tauopathy… svPPA… 72% FTLD-TDP.” (JNNP, 2024) (shir2024clinicoradiologicalandneuropathological pages 1-2). - “Apraxia of speech… strongly predicted 4R-tau (PSP/CBD)… ‘pure’ agrammatic… associated with 3R-tau (PiD).” (JNNP, 2024) (shir2024clinicoradiologicalandneuropathological pages 8-10, shir2024clinicoradiologicalandneuropathological pages 1-2). - “The three PPA subtypes show distinct regions of hypometabolism in FDG-PET imaging: SD anterior temporal, LPA left temporo-parietal junction, nfvPPA left inferior frontal gyrus and insula.” (Ann Nucl Med, 2024) (mirbod2024fdgpetinthe pages 1-2). - “Repetition-impaired PPA subgroups [pure-LPA, Wernicke-like, TCSA-like] were uniformly AD.” (Neurology, 2024) (watanabe2024primaryprogressiveaphasia pages 1-2). - “PGRN deficiency… cytoplasmic TDP-43 aggregation… lipid droplets… lysosomal abnormalities… mediated by complement C1q activation.” (J Neuroinflammation, 2024) (sung2024progranulinhaploinsufficiencymediates pages 1-2). - “CSF progranulin increased after PR006 treatment in all patients… CSF pleocytosis most common adverse event… transient NfL increases.” (Nat Med, 2024) (sevigny2024progranulinaavgene pages 1-2).

Concluding synthesis

PPA pathophysiology reflects convergent protein misfolding diseases with variant-specific epicenters in the left language network and predictable spread across connected systems. Robust 2023–2024 evidence refines clinicopathological links (lvPPA→AD; nfvPPA→tau with apraxia-of-speech–based 3R/4R stratification; svPPA→FTLD-TDP type C), consolidates imaging signatures (FDG-PET and MRI), and introduces machine-learning tools that improve in vivo proteinopathy prediction. Parallel advances in GRN-related FTLD illuminate lysosomal–glial mechanisms relevant to PPA phenotypes and support translational biomarker development and first-in-human progranulin gene therapy.

References

(shir2024clinicoradiologicalandneuropathological pages 1-2): Dror Shir, Nick Corriveau-Lecavalier, Camilo Bermudez Noguera, Leland Barnard, Nha Trang Thu Pham, Hugo Botha, Joseph R Duffy, Heather M Clark, Rene L Utianski, David S Knopman, Ronald C Petersen, Bradley F Boeve, Melissa E Murray, Aivi T Nguyen, R Ross Reichard, Dennis W Dickson, Gregory S Day, Walter K Kremers, Neill R Graff-Radford, David T Jones, Mary M Machulda, Julie A Fields, Jennifer L Whitwell, Keith A Josephs, and Jonathan Graff-Radford. Clinicoradiological and neuropathological evaluation of primary progressive aphasia. Journal of Neurology, Neurosurgery, and Psychiatry, 95:812-821, Mar 2024. URL: https://doi.org/10.1136/jnnp-2023-332862, doi:10.1136/jnnp-2023-332862. This article has 9 citations.
(watanabe2024primaryprogressiveaphasia pages 1-2): Hiroyuki Watanabe, Joseph R. Duffy, Heather Clark, Mary M. Machulda, Jonathan Graff-Radford, Nha Trang Thu Pham, Dennis W. Dickson, Val J. Lowe, Jennifer L. Whitwell, and Keith A. Josephs. Primary progressive aphasia lacking core features of nonfluent and semantic variants: clinical, neuroimaging, and neuropathologic features. Neurology, 103 9:e209924, Nov 2024. URL: https://doi.org/10.1212/wnl.0000000000209924, doi:10.1212/wnl.0000000000209924. This article has 11 citations and is from a highest quality peer-reviewed journal.
(mirbod2024fdgpetinthe pages 1-2): Melika Mirbod, Cyrus Ayubcha, Hyae Won Kim Redden, Eric Teichner, Robert C. Subtirelu, Raj Patel, William Raynor, Thomas Werner, Abass Alavi, and Mona-Elisabeth Revheim. Fdg-pet in the diagnosis of primary progressive aphasia: a systematic review. Annals of Nuclear Medicine, 38:673-687, Jul 2024. URL: https://doi.org/10.1007/s12149-024-01958-w, doi:10.1007/s12149-024-01958-w. This article has 4 citations and is from a peer-reviewed journal.
(shir2024clinicoradiologicalandneuropathological pages 8-10): Dror Shir, Nick Corriveau-Lecavalier, Camilo Bermudez Noguera, Leland Barnard, Nha Trang Thu Pham, Hugo Botha, Joseph R Duffy, Heather M Clark, Rene L Utianski, David S Knopman, Ronald C Petersen, Bradley F Boeve, Melissa E Murray, Aivi T Nguyen, R Ross Reichard, Dennis W Dickson, Gregory S Day, Walter K Kremers, Neill R Graff-Radford, David T Jones, Mary M Machulda, Julie A Fields, Jennifer L Whitwell, Keith A Josephs, and Jonathan Graff-Radford. Clinicoradiological and neuropathological evaluation of primary progressive aphasia. Journal of Neurology, Neurosurgery, and Psychiatry, 95:812-821, Mar 2024. URL: https://doi.org/10.1136/jnnp-2023-332862, doi:10.1136/jnnp-2023-332862. This article has 9 citations.
(shir2024clinicoradiologicalandneuropathological pages 4-6): Dror Shir, Nick Corriveau-Lecavalier, Camilo Bermudez Noguera, Leland Barnard, Nha Trang Thu Pham, Hugo Botha, Joseph R Duffy, Heather M Clark, Rene L Utianski, David S Knopman, Ronald C Petersen, Bradley F Boeve, Melissa E Murray, Aivi T Nguyen, R Ross Reichard, Dennis W Dickson, Gregory S Day, Walter K Kremers, Neill R Graff-Radford, David T Jones, Mary M Machulda, Julie A Fields, Jennifer L Whitwell, Keith A Josephs, and Jonathan Graff-Radford. Clinicoradiological and neuropathological evaluation of primary progressive aphasia. Journal of Neurology, Neurosurgery, and Psychiatry, 95:812-821, Mar 2024. URL: https://doi.org/10.1136/jnnp-2023-332862, doi:10.1136/jnnp-2023-332862. This article has 9 citations.
(shir2024clinicoradiologicalandneuropathological pages 10-11): Dror Shir, Nick Corriveau-Lecavalier, Camilo Bermudez Noguera, Leland Barnard, Nha Trang Thu Pham, Hugo Botha, Joseph R Duffy, Heather M Clark, Rene L Utianski, David S Knopman, Ronald C Petersen, Bradley F Boeve, Melissa E Murray, Aivi T Nguyen, R Ross Reichard, Dennis W Dickson, Gregory S Day, Walter K Kremers, Neill R Graff-Radford, David T Jones, Mary M Machulda, Julie A Fields, Jennifer L Whitwell, Keith A Josephs, and Jonathan Graff-Radford. Clinicoradiological and neuropathological evaluation of primary progressive aphasia. Journal of Neurology, Neurosurgery, and Psychiatry, 95:812-821, Mar 2024. URL: https://doi.org/10.1136/jnnp-2023-332862, doi:10.1136/jnnp-2023-332862. This article has 9 citations.
(sung2024progranulinhaploinsufficiencymediates pages 1-2): Wonjae Sung, Min-Young Noh, Minyeop Nahm, Yong Sung Kim, Chang-Seok Ki, Young-Eun Kim, Hee-Jin Kim, and Seung Hyun Kim. Progranulin haploinsufficiency mediates cytoplasmic tdp-43 aggregation with lysosomal abnormalities in human microglia. Journal of Neuroinflammation, Feb 2024. URL: https://doi.org/10.1186/s12974-024-03039-1, doi:10.1186/s12974-024-03039-1. This article has 20 citations and is from a peer-reviewed journal.
(hsiaonakamoto2024alterationsinlysosomal pages 1-5): Jennifer Hsiao-Nakamoto, Chi-Lu Chiu, Lawren VandeVrede, Ritesh Ravi, Brittany Vandenberg, Jack De Groot, Buyankhishig Tsogtbaatar, Meng Fang, Paul Auger, Neal S. Gould, Filippo Marchioni, Casey A. Powers, Sonnet S. Davis, Jung H. Suh, Jamal Alkabsh, Hilary W. Heuer, Argentina Lario Lago, Kimberly Scearce-Levie, William W. Seeley, Bradley F. Boeve, Howard J. Rosen, Amy Berger, Richard Tsai, Gilbert Di Paolo, Adam L. Boxer, Akhil Bhalla, and Fen Huang. Alterations in lysosomal, glial and neurodegenerative biomarkers in patients with sporadic and genetic forms of frontotemporal dementia. bioRxiv, Feb 2024. URL: https://doi.org/10.1101/2024.02.09.579529, doi:10.1101/2024.02.09.579529. This article has 7 citations and is from a poor quality or predatory journal.
(hsiaonakamoto2024alterationsinlysosomal pages 27-30): Jennifer Hsiao-Nakamoto, Chi-Lu Chiu, Lawren VandeVrede, Ritesh Ravi, Brittany Vandenberg, Jack De Groot, Buyankhishig Tsogtbaatar, Meng Fang, Paul Auger, Neal S. Gould, Filippo Marchioni, Casey A. Powers, Sonnet S. Davis, Jung H. Suh, Jamal Alkabsh, Hilary W. Heuer, Argentina Lario Lago, Kimberly Scearce-Levie, William W. Seeley, Bradley F. Boeve, Howard J. Rosen, Amy Berger, Richard Tsai, Gilbert Di Paolo, Adam L. Boxer, Akhil Bhalla, and Fen Huang. Alterations in lysosomal, glial and neurodegenerative biomarkers in patients with sporadic and genetic forms of frontotemporal dementia. bioRxiv, Feb 2024. URL: https://doi.org/10.1101/2024.02.09.579529, doi:10.1101/2024.02.09.579529. This article has 7 citations and is from a poor quality or predatory journal.
(tetzloff2023amyloidandtau pages 1-3): Katerina A. Tetzloff, Joseph R. Duffy, Heather M. Clark, Nha Trang Thu Pham, Mary M. Machulda, Hugo Botha, Clifford R. Jack, Dennis W. Dickson, Val J. Lowe, Keith A. Josephs, Jennifer L. Whitwell, and Rene L. Utianski. Amyloid and tau pet positivity in progressive agrammatic aphasia and apraxia of speech. Journal of Alzheimer's Disease, 96:1759-1765, Dec 2023. URL: https://doi.org/10.3233/jad-230912, doi:10.3233/jad-230912. This article has 2 citations and is from a peer-reviewed journal.
(sevigny2024progranulinaavgene pages 1-2): Jeffrey Sevigny, Olga Uspenskaya, Laura Dean Heckman, Li Chin Wong, Daniel A. Hatch, Ambika Tewari, Rik Vandenberghe, David J. Irwin, Dario Saracino, Isabelle Le Ber, Rebekah Ahmed, Jonathan D. Rohrer, Adam L. Boxer, Sebastian Boland, Patricia Sheehan, Alissa Brandes, Suzanne R. Burstein, Benjamin M. Shykind, Sitharthan Kamalakaran, Carter W. Daniels, E. David Litwack, Erin Mahoney, Jenny Velaga, Ilan McNamara, Patricia Sondergaard, Syed A. Sajjad, Yvonne M. Kobayashi, Asa Abeliovich, and Franz Hefti. Progranulin aav gene therapy for frontotemporal dementia: translational studies and phase 1/2 trial interim results. Nature Medicine, 30:1406-1415, May 2024. URL: https://doi.org/10.1038/s41591-024-02973-0, doi:10.1038/s41591-024-02973-0. This article has 56 citations and is from a highest quality peer-reviewed journal.
(hsiaonakamoto2024alterationsinlysosomal pages 38-41): Jennifer Hsiao-Nakamoto, Chi-Lu Chiu, Lawren VandeVrede, Ritesh Ravi, Brittany Vandenberg, Jack De Groot, Buyankhishig Tsogtbaatar, Meng Fang, Paul Auger, Neal S. Gould, Filippo Marchioni, Casey A. Powers, Sonnet S. Davis, Jung H. Suh, Jamal Alkabsh, Hilary W. Heuer, Argentina Lario Lago, Kimberly Scearce-Levie, William W. Seeley, Bradley F. Boeve, Howard J. Rosen, Amy Berger, Richard Tsai, Gilbert Di Paolo, Adam L. Boxer, Akhil Bhalla, and Fen Huang. Alterations in lysosomal, glial and neurodegenerative biomarkers in patients with sporadic and genetic forms of frontotemporal dementia. bioRxiv, Feb 2024. URL: https://doi.org/10.1101/2024.02.09.579529, doi:10.1101/2024.02.09.579529. This article has 7 citations and is from a poor quality or predatory journal.