title: Frontotemporal lobar degeneration: Pathogenesis, pathology and pathways to phenotype.
abstract: Frontotemporal Lobar Degeneration (FTLD) is a clinically, pathologically and genetically heterogeneous group of disorders that affect principally the frontal and temporal lobes of the brain. 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. All three clinical syndromes can exist separately or in combination with Amyotrophic Lateral Sclerosis (ALS). SD is exclusively a TDP-43 proteinopathy, and PNFA may be so, with both showing tight clinical, histological and genetic inter-relationships. bvFTD is more of a challenge with overlapping histological and genetic features, involvement of any of the three aggregating proteins, and changes in any of the three major genes. However, when ALS is present, all cases show a clear histological phenotype with TDP-43 aggregated proteins, and familial forms are associated with expansions in C9orf72. TDP-43 and FUS are nuclear carrier proteins involved in the regulation of RNA metabolism, whereas tau protein - the product of MAPT - is responsible for the assembly/disassembly of microtubules, which are vital for intracellular transport. Mutations in TDP-43 and FUS genes are linked to clinical ALS rather than FTLD (with or without ALS), suggesting that clinical ALS may be a disorder of RNA metabolism. Conversely, the protein products of GRN and C9orf72, along with those of the other minor genes, appear to form part of the cellular protein degradation machinery. It is possible therefore that FTLD is a reflection of dysfunction within lysosomal/proteasomal systems resulting in failure to remove potentially neurotoxic (TDP-43 and tau) aggregates, which ultimately overwhelm capacity to function. Spread of aggregates along distinct pathways may account for the different clinical phenotypes, and patterns of progression of disease.
authors.affiliation: Division of Neuroscience and Experimental Psychology, School of Biological Sciences, Faculty of Medical and Human Sciences, University of Manchester, Salford Royal Hospital, Salford, M6 8HD, UK.
authors.forename: David M A
authors.initials: DMA
authors.lastname: Mann
authors.affiliation: Division of Neuroscience and Experimental Psychology, School of Biological Sciences, Faculty of Medical and Human Sciences, University of Manchester, Salford Royal Hospital, Salford, M6 8HD, UK.|Cerebral Function Unit, Greater Manchester Neurosciences Centre, Salford Royal Hospital, Stott Lane, Salford, M6 8HD, UK.
authors.forename: Julie S
authors.initials: JS
authors.lastname: Snowden
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics; D001037:Aphasia / Q000473:pathology; D001921:Brain / Q000473:pathology; D000073885:C9orf72 Protein / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D057180:Frontotemporal Dementia / Q000473:pathology; D057174:Frontotemporal Lobar Degeneration / Q000235:genetics* / Q000473:pathology*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D009154:Mutation; D010641:Phenotype; D000077153:Progranulins; D034702:RNA-Binding Protein FUS / Q000235:genetics; D057177:TDP-43 Proteinopathies / Q000235:genetics; D016875:tau Proteins / Q000235:genetics
chemical_list: D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D004268:DNA-Binding Proteins; C492314:GRN protein, human; D036341:Intercellular Signaling Peptides and Proteins; C054369:MAPT protein, human; D000077153:Progranulins; D034702:RNA-Binding Protein FUS; D016875:tau Proteins
keywords: clinical phenotypes; frontotemporal lobar degeneration; genetics; neuropathology; pathogenesis