Cerebellar c9RAN proteins associate with clinical and neuropathological characteristics of C9ORF72 repeat expansion carriers.

Dennis W Dickson,Colleen S Thomas,Lillian M Daughrity,John A Lucas,Pamela Desaro,Bradley F Boeve,Monica Castanedes‐Casey ,Dieter Edbauer,David S Knopman,Jie Jiang,Kevin B Boylan,Beth Rush ,Linda Rousseau,A Robertson ,Clotilde Lagier‐Tourenne ,Kevin F Bieniek,Melissa E Murray,Julia E Crook,Rosa Rademakers,Karen Overstreet,Neill R Graff‐Radford ,Leonard Petrucelli,Joseph E Parisi,Marka Van Blitterswijk,Otto Pedraza,Tania F Gendron,Don W Cleveland,Ronald C Petersen,Keith A Josephs

doi:10.1007/s00401-015-1474-4

Abstract

Clinical and neuropathological characteristics associated with G4C2 repeat expansions in chromosome 9 open reading frame 72 (C9ORF72), the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia, are highly variable. To gain insight on the molecular basis for the heterogeneity among C9ORF72 mutation carriers, we evaluated associations between features of disease and levels of two abundantly expressed “c9RAN proteins” produced by repeat-associated non-ATG (RAN) translation of the expanded repeat. For these studies, we took a departure from traditional immunohistochemical approaches and instead employed immunoassays to quantitatively measure poly(GP) and poly(GA) levels in cerebellum, frontal cortex, motor cortex, and/or hippocampus from 55 C9ORF72 mutation carriers [12 patients with ALS, 24 with frontotemporal lobar degeneration (FTLD) and 19 with FTLD with motor neuron disease (FTLD-MND)]. We additionally investigated associations between levels of poly(GP) or poly(GA) and cognitive impairment in 15 C9ORF72 ALS patients for whom neuropsychological data were available. Among the neuroanatomical regions investigated, poly(GP) levels were highest in the cerebellum. In this same region, associations between poly(GP) and both neuropathological and clinical features were detected. Specifically, cerebellar poly(GP) levels were significantly lower in patients with ALS compared to patients with FTLD or FTLD-MND. Furthermore, cerebellar poly(GP) associated with cognitive score in our cohort of 15 patients. In the cerebellum, poly(GA) levels similarly trended lower in the ALS subgroup compared to FTLD or FTLD-MND subgroups, but no association between cerebellar poly(GA) and cognitive score was detected. Both cerebellar poly(GP) and poly(GA) associated with C9ORF72 variant 3 mRNA expression, but not variant 1 expression, repeat size, disease onset, or survival after onset. Overall, these data indicate that cerebellar abnormalities, as evidenced by poly(GP) accumulation, associate with neuropathological and clinical phenotypes, in particular cognitive impairment, of C9ORF72 mutation carriers.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-015-1474-4) contains supplementary material, which is available to authorized users.

Highlights

Amyotrophic lateral sclerosis (ALS), the most common motor neuron disease (MND), is characterized by progressive upper and lower motor neuron weakness, typically resulting in death from ventilatory failure within three to five years of onset
Given our findings above and the fact that poly(GA) pathology is abundant in the cerebellum (Fig. 5a), and given a recent report showing that poly(GA) inclusion burden in cerebellar granule cells correlated with neuropathological subgroup [30], we investigated whether cerebellar poly(GA) levels assessed by immunoassay differ based on neuropathological diagnosis or cognitive score in our case series
We show that cerebellar poly(GP) levels were significantly lower in ALS patients compared to frontotemporal lobar degeneration (FTLD) and FTLD-MND patients

Summary

Introduction

Amyotrophic lateral sclerosis (ALS), the most common motor neuron disease (MND), is characterized by progressive upper and lower motor neuron weakness, typically resulting in death from ventilatory failure within three to five years of onset. The clinical overlap between ALS and FTD, combined with neuropathological similarities—TDP-43 pathology is present in the majority of ALS cases and the most common pathological subtype of FTLD (FTLD-TDP)—suggest ALS and FTD are part of a disease spectrum. This concept was strengthened by the discovery that a G4C2 repeat expansion in chromosome 9 open reading frame 72 (C9ORF72) is the most common genetic cause of ALS and FTD [10, 28]. C9RAN protein pathology, in particular inclusions of poly(GP) or poly(GA), is abundant in cerebellum, hippocampus, and neocortical regions [3, 16, 18, 21, 22, 30, 43]

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