The clinical and pathological phenotype of C9ORF72 hexanucleotide repeat expansions

Abstract

There is increasing evidence that frontotemporal dementia and amyotrophic lateral sclerosis are part of a disease continuum. Recently, a hexanucleotide repeat expansion in C9orf72 was identified as a major cause of both sporadic and familial frontotemporal dementia and amyotrophic lateral sclerosis. The aim of this study was to investigate clinical and neuropathological characteristics of hexanucleotide repeat expansions in C9orf72 in a large cohort of Dutch patients with frontotemporal dementia. Repeat expansions were successfully determined in a cohort of 353 patients with sporadic or familial frontotemporal dementia with or without amyotrophic lateral sclerosis, and 522 neurologically normal controls. Immunohistochemistry was performed in a series of 10 brains from patients carrying expanded repeats using a panel of antibodies. In addition, the presence of RNA containing GGGGCC repeats in paraffin-embedded sections of post-mortem brain tissue was investigated using fluorescence in situ hybridization with a locked nucleic acid probe targeting the GGGGCC repeat. Hexanucleotide repeat expansions in C9orf72 were found in 37 patients with familial (28.7%) and five with sporadic frontotemporal dementia (2.2%). The mean age at onset was 56.9 ± 8.3 years (range 39-76), and disease duration 7.6 ± 4.6 years (range 1-22). The clinical phenotype of these patients varied between the behavioural variant of frontotemporal dementia (n = 34) and primary progressive aphasia (n = 8), with concomitant amyotrophic lateral sclerosis in seven patients. Predominant temporal atrophy on neuroimaging was present in 13 of 32 patients. Pathological examination of the 10 brains from patients carrying expanded repeats revealed frontotemporal lobar degeneration with neuronal transactive response DNA binding protein-positive inclusions of variable type, size and morphology in all brains. Fluorescence in situ hybridization analysis of brain material from patients with the repeat expansion, a microtubule-associated protein tau or a progranulin mutation, and controls did not show RNA-positive inclusions specific for brains with the GGGGCC repeat expansion. The hexanucleotide repeat expansion in C9orf72 is an important cause of frontotemporal dementia with and without amyotrophic lateral sclerosis, and is sometimes associated with primary progressive aphasia. Neuropathological hallmarks include neuronal and glial inclusions, and dystrophic neurites containing transactive response DNA binding protein. Future studies are needed to explain the wide variation in clinical presentation.

Isoform‐specific antibodies reveal distinct subcellular localizations of C9orf72 in amyotrophic lateral sclerosis

“…In contrast, C9-S antibody gave a very specific labeling of the nuclear membrane, clearly showing that C9-L and C9-S have different subcellular localizations in Purkinje cells. Previously published reports using commercial antibodies against C9orf72 protein have noted diffuse and granular staining in neuronal cytoplasm and neurites; however, these antibodies show high levels of nonspecific staining and are either unable to discriminate between C9-L and C9-S or are solely directed against C9-L. 11,12,15,16,40,44 Thus, our antibodies provide greatly improved detection of C9orf72 protein isoforms and have revealed distinct subcellular localizations of C9-L and C9-S. Immunohistochemical labeling of spinal cord tissue showed that the subcellular localization of C9-L in diseased motor neurons appeared unchanged in c9-ALS and non-c9-ALS cases compared to controls. However, changes in the relative intensity of staining between cases were apparent, with some c9-ALS cases showing a relative increase in labeling and others a decrease.…”

“…1,2,5,6 Patients carrying the expansion can show heterogeneous clinical presentation, and the expansion has been identified in patients with other neurological diseases. 1,2,[7][8][9][10][11][12][13][14][15][16][17][18][19] Three potential pathomechanisms have been proposed to arise from the repeat expansion in C9orf72: RNAmediated toxicity through generation of RNA foci and sequestration of RNA-binding proteins from their normal targets; expression of dipeptide repeat proteins by repeatassociated non-ATG (RAN) translation; and haploinsufficiency. 1,2,[20][21][22][23] C9orf72 generates three transcripts through alternative splicing that encode 2 protein isoforms; a long isoform of approximately 54 kDa (termed C9-L), corresponding to variants 2 (V2) and 3 (V3), and a short isoform of approximately 24 kDa (termed C9-S) corresponding to variant 1 (V1).…”

Drosophila as an In Vivo Model for Human Neurodegenerative Disease

“…However, pathology specific to C9orf72 carriers include RNA foci hybridizing to both the sense GGGGCC repeat RNA, as well as the antisense GGCCCC repeat RNA, in spinal cord and multiple brain regions, implicating an RNA gain-of-function mechanism Simon-Sanchez et al 2012;Donnelly et al 2013;Gendron et al 2013;LagierTourenne et al 2013;Lee et al 2013;Mizielinska et al 2013). An additional pathology found in GGGGCC repeat carriers is the cerebellar, hippocampal, and cortical accumulation of TDP-43 negative inclusions that are positive for proteins in the ubiquitin-proteasome pathway (Mackenzie et al 2014).…”

C9orf72-related disorders: expanding the clinical and genetic spectrum of neurodegenerative diseases

“…Neuropsychiatric profile involves early disinhibition (up to 85%), lack of insight (up to 78%), hallucinations (up to 50%), delusion (up to 50%), anxiety (up to 52%), hyperorality (up to 100%), early apathy (up to 100%), loss of empathy (up to 77%) and obsessive-compulsive symptoms (up to 12%) 5,42,43 . There is an important clinical overlap with probable Alzheimer's disease in the early-onset cases, mainly in Caucasian patients 45,46 , making it difficult to promote a proper genetic evaluation in association with classical genes (APP, PSEN1, PSEN2) 47,48 , although such cases generally present with an older age than with the FTD clinical spectrum 26 . UBQLN2 gene mutations are great mimickers frequently differentiated in clinical means by the absence of psychiatric features (not behavioural symptoms) and lower motor neuron involvement 14 .…”