CSF-Progranulin levels were significantly lower in FTD type patients with semantic dementia and behavioral variant FTD mainly attributed to the Tar-DNA-Binding-Protein (TDP) 43 compared to predominantly Tau-mediated PNFA (<i>p</i> < 0.05).
There are three major associated clinical syndromes, behavioral variant frontotemporal dementia (bvFTD), semantic dementia (SD) and progressive non-fluent aphasia (PNFA); three principal histologies, involving tau, TDP-43 and FUS proteins; and mutations in three major genes, MAPT, GRN and C9orf72, along with several other less common gene mutations.
In particular, mutations in GRN account for 5-10% of all cases and give rise to a wide spectrum of clinical phenotypes, ranging from behavioral frontotemporal dementia (bvFTD) to primary progressive aphasia, including progressive non-fluent aphasia (PNFA) and semantic dementia, and corticobasal syndrome (CBS).
Progranulin gene (GRN) mutations cause frontotemporal lobar degeneration (FTLD) with TDP43-positive inclusions, although its clinical phenotype is heterogeneous and includes patients classified as behavioral variant-FTLD (bvFTLD), progressive non-fluent aphasia (PNFA), corticobasal syndrome, Alzheimer's disease (AD), or Parkinson's disease (PD).
Here we undertook a systematic study of nonverbal sound processing in patient groups with canonical dementia syndromes comprising clinically diagnosed typical amnestic Alzheimer's disease (AD; n=21), progressive nonfluent aphasia (PNFA; n=5), logopenic progressive aphasia (LPA; n=7) and aphasia in association with a progranulin gene mutation (GAA; n=1), and in healthy age-matched controls (n=20).
Certain prominent features of this case (in particular, the profile of semantic impairment) have not been emphasised in previous descriptions of LPA or PNFA, suggesting that GRN may cause an overlapping PPA syndrome but with a distinctive cognitive profile.
The importance of these findings is threefold: firstly, the clinico-anatomical entity of LPA has a profile of brain damage that is complementary to the network-based disorders of SD and PNFA; secondly, the core phonological processing deficit in LPA is likely to arise from temporo-parietal junction damage but disease spread occurs through the dorsal language network (and in GRN-PPA, also the ventral language network); and finally, GRN mutations provide a specific molecular substrate for language network dysfunction.
33 PPA patients (9 semantic dementia, SD, 14 progressive nonfluent aphasia, PNFA, 7 logopenic/phonological aphasia, LPA and 3 patients with a PPA syndrome in association with progranulin mutations, GRN-PPA) were assessed using the Neuropsychiatric Inventory to record behavioural changes, as well as volumetric MR imaging.