Structural and microstructural neuroimaging signature of C9orf72-associated ALS: A multiparametric MRI study

BACKGROUND

ALS patients with hexanucleotide expansion in C9orf72 are characterized by a specific clinical phenotype, including more aggressive disease course and cognitive decline. Computerized multiparametric MRI with gray matter volumetry and diffusion tensor imaging (DTI) to analyze white matter structural connectivity is a potential in vivo biomarker.

OBJECTIVE

The objective of this study was to develop a multiparametric MRI signature in a large cohort of ALS patients with C9orf72 mutations. The aim was to investigate how morphological features of C9orf72-associated ALS differ in structural MRI and DTI compared to healthy controls and ALS patients without C9orf72 mutations.

METHODS

Atlas-based volumetry (ABV) and whole brain-based DTI-based analyses were performed in a cohort of n = 51 ALS patients with C9orf72 mutations and compared with both n = 51 matched healthy controls and n = 51 C9orf72 negative ALS patients, respectively. Subsequently, Spearman correlation analysis of C9orf72 ALS patients' data with clinical parameters (age of onset, sex, ALS-FRS-R, progression rate, survival) as well as ECAS and p-NfH in CSF was performed.

RESULTS

The whole brain voxel-by-voxel comparison of fractional anisotropy (FA) maps between C9orf72 ALS patients and controls showed significant bilateral alterations in axonal structures of the white matter at group level, primarily along the corticospinal tracts and in fibers projecting to the frontal lobes. For the frontal lobes, these alterations were also significant between C9orf72 positive and C9orf72 negative ALS patients. In ABV, patients with C9orf72 mutations showed lower volumes of the frontal, temporal, and parietal lobe, with the lowest values in the gray matter of the superior frontal and the precentral gyrus, but also in hippocampi and amygdala. Compared to C9orf72 negative ALS, the differences were shown to be significant for cerebral gray matter (p = 0.04), especially in the frontal (p = 0.01) and parietal lobe (p = 0.01), and in the thalamus (p = 0.004). A correlation analysis between ECAS and averaged regional FA values revealed significant correlations between cognitive performance in ECAS and frontal association fibers. Lower FA values in the frontal lobes were associated with worse performance in all cognitive domains measured (language, verbal fluency, executive functions, memory and spatial perception). In addition, there were significant negative correlations between age of onset and atlas-based volumetry results for gray matter.

CONCLUSIONS

This study demonstrates a distinct pattern of DTI alterations of the white matter and ubiquitous volume reductions of the gray matter early in the disease course of C9orf72-associated ALS. Alterations were closely linked to a more aggressive cognitive phenotype. These results are in line with an expected pTDP43 propagation pattern of cortical affection and thus strengthen the hypothesis that an underlying developmental disorder is present in ALS with C9orf72 expansions. Thus, multiparametric MRI could contribute to the assessment of the disease as an in vivo biomarker even in the early phase of the disease.

Segmental involvement of the corpus callosum in C9orf72-associated ALS: a tract of interest-based DTI study

Background:

C9orf72 hexanucleotide repeat expansions are associated with widespread cerebral alterations, including white matter alterations. However, there is lack of information on changes in commissure fibres. Diffusion tensor imaging (DTI) can identify amyotrophic lateral sclerosis (ALS)-associated patterns of regional brain alterations at the group level. The objective of this study was to investigate the structural connectivity of the corpus callosum (CC) in ALS patients with C9orf72 expansions.

Methods:

DTI-based white matter mapping was performed by a hypothesis-guided tractwise analysis of fractional anisotropy (FA) maps for 25 ALS patients with C9orf72 expansion versus 25 matched healthy controls. Furthermore, a comparison with a patient control group of 25 sporadic ALS patients was performed. DTI-based tracts that originate from callosal sub-areas I to V were identified and correlated with clinical data.

Results:

The analysis of white matter integrity demonstrated regional FA reductions for tracts of the callosal areas II and III for ALS patients with C9orf72 expansions while FA reductions in sporadic ALS patients were observed only for tracts of the callosal area III; these reductions were correlated with clinical parameters.

Conclusion:

The tract-of-interest-based analysis showed a microstructural callosal involvement pattern in C9orf72-associated ALS that included the motor segment III together with frontal callosal connections, as an imaging signature of the C9orf72-associated overlap of motor neuron disease and frontotemporal pathology.

In vivo histopathological staging in C9orf72-associated ALS: A tract of interest DTI study

BACKGROUND

Diffusion tensor imaging (DTI) can identify amyotrophic lateral sclerosis (ALS)-associated patterns of brain alterations at the group level according to a neuropathological staging system.

OBJECTIVE

The study was designed to investigate the in vivo staging in ALS patients with the C9orf72 expansion and potential differences to ALS patients with the SOD1 mutation.

METHODS

DTI-based white matter mapping was performed both by an unbiased voxel-wise statistical comparison and by a hypothesis-guided tract-wise analysis of fractional anisotropy (FA) maps according to the ALS-staging pattern for 27 ALS patients with C9orf72 expansion vs 15 ALS patients with SOD1 mutation vs 32 matched healthy controls. Clinical and neuropsychological data were acquired and correlated to DTI data.

RESULTS

The analysis of white matter integrity demonstrated regional FA reductions along the CST and also in frontal and prefrontal brain areas according to the proposed propagation pattern for the ALS patients with C9orf72 expansion and sporadic patients. This pattern could not be identified for the SOD1 mutation at the group level. In contrast, in the tract-specific analysis according to the neuropathological ALS-staging pattern, C9orf72 expansion ALS patients showed significant alterations of ALS-related tract systems similar to sporadic patients.

CONCLUSIONS

The DTI study including the tract-of-interest-based analysis showed a microstructural corticoefferent involvement pattern according to the staging scheme in C9orf72-associated ALS patients but not in the SOD1 mutation.

Oligogenicity, C9orf72 expansion, and variant severity in ALS

"Oligogenic inheritance" is used to describe cases where more than one rare pathogenic variant is observed in the same individual. While multiple variants can alter disease presentation, the necessity of multiple variants to instigate pathogenesis has not been addressed in amyotrophic lateral sclerosis (ALS). We sequenced ALS-associated genes in C9orf72-expansion-positive and negative ALS patients, alongside unaffected controls, to test the importance of oligogenicity and variant deleteriousness in ALS. We found that all groups had similar numbers of rare variants, but that variant severity was significantly higher in C9orf72-negative ALS cases, suggesting sufficiency of C9orf72 expansion to cause ALS alone.

Chimeric Peptide Species Contribute to Divergent Dipeptide Repeat Pathology in c9ALS/FTD and SCA36

GGGGCC hexanucleotide repeat expansions (HREs) in C9orf72 cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) and lead to the production of aggregating dipeptide repeat proteins (DPRs) via repeat associated non-AUG (RAN) translation. Here, we show the similar intronic GGCCTG HREs that causes spinocerebellar ataxia type 36 (SCA36) is also translated into DPRs, including poly(GP) and poly(PR). We demonstrate that poly(GP) is more abundant in SCA36 compared to c9ALS/FTD patient tissue due to canonical AUG-mediated translation from intron-retained GGCCTG repeat RNAs. However, the frequency of the antisense RAN translation product poly(PR) is comparable between c9ALS/FTD and SCA36 patient samples. Interestingly, in SCA36 patient tissue, poly(GP) exists as a soluble species, and no TDP-43 pathology is present. We show that aggregate-prone chimeric DPR (cDPR) species underlie the divergent DPR pathology between c9ALS/FTD and SCA36. These findings reveal key differences in translation, solubility, and protein aggregation of DPRs between c9ALS/FTD and SCA36.

Prevalence of C9orf72 hexanucleotide repeat expansion in Greek patients with sporadic ALS

A total of 178 consecutive patients with definite sALS without frontotemporal dementia (FTD) were enrolled in this study, after complete clinical evaluation. A Repeat-Primed Polymerase Chain Reaction (RP-PCR) protocol was applied to detect the G₄C₂ repeats expansions. In the studied sALS patients, 5.06% (n = 9) carried the C9orf72 mutation. Among carriers, 2/3 of them were females and spinal onset accounted for 78% and bulbar for 22%, while the mean age of onset was about 60 years. Our study showed that the prevalence of C9orf72 repeat expansion in Greek sALS patients is similar to the overall frequency of the mutation in European populations. The pathogenic mutation remains a promising biomarker for genetic testing and targeted treatment.

Comparative Analysis of C9orf72 and Sporadic Disease in a Large Multicenter ALS Population: The Effect of Male Sex on Survival of C9orf72 Positive Patients

We investigated whether the C9orf72 repeat expansion is associated with specific clinical features, comorbidities, and prognosis in patients with amyotrophic lateral sclerosis (ALS). A cohort of 1417 ALS patients, diagnosed between January 1, 2009 and December 31, 2013 by 13 Italian ALS Referral Centers, was screened for the C9orf72 repeat expansion, and the analyses were performed comparing patients carrying this expansion (ALS-C9Pos) to those negative for this and other explored ALS-related mutations (ALS without genetic mutations, ALSwoGM). Compared to the ALSwoGM group, ALS-C9Pos patients (n = 84) were younger at disease onset, at the first clinical observation and at diagnosis (p < 0.001). After correcting for these differences, we found that ALS-C9Pos patients had higher odds of bulbar onset, diagnosis of frontotemporal dementia (FTD) and family history of ALS, FTD, and Alzheimer's disease and had lower odds of spinal onset, non-invasive ventilation, hypertension and psychiatric diseases than ALSwoGM patients. Among these variables, those related to shorter survival time were: bulbar onset, presence of FTD, hypertension, psychiatric disease, and family history of ALS (p < 0.05). Cox proportional hazards regression multivariate analysis suggested that carrying the C9orf72 repeat expansion was an independent factor negatively impacting on survival time in men (HR 1.58, 95% CI 1.07–2.33, p = 0.021), but not in women (p > 0.05) as well as in the whole sample (p > 0.05). When compared to ALSwoGM, ALS-C9Pos showed an earlier disease onset, no significant diagnostic delay and a higher odds of bulbar onset, FTD and family history of ALS and dementia. Moreover, male sex drove the negative effect of expanded variant on survival, confirming the hypothesis that sex is likely to be a crucial factor in the biology of C9orf72-related disease.

Astrocytes and Microglia as Potential Contributors to the Pathogenesis of C9orf72 Repeat Expansion-Associated FTLD and ALS

Frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases with a complex, but often overlapping, genetic and pathobiological background and thus they are considered to form a disease spectrum. Although neurons are the principal cells affected in FTLD and ALS, increasing amount of evidence has recently proposed that other central nervous system-resident cells, including microglia and astrocytes, may also play roles in neurodegeneration in these diseases. Therefore, deciphering the mechanisms underlying the disease pathogenesis in different types of brain cells is fundamental in order to understand the etiology of these disorders. The major genetic cause of FTLD and ALS is a hexanucleotide repeat expansion (HRE) in the intronic region of the C9orf72 gene. In neurons, specific pathological hallmarks, including decreased expression of the C9orf72 RNA and proteins and generation of toxic RNA and protein species, and their downstream effects have been linked to C9orf72 HRE-associated FTLD and ALS. In contrast, it is still poorly known to which extent these pathological changes are presented in other brain cells. Here, we summarize the current literature on the potential role of astrocytes and microglia in C9orf72 HRE-linked FTLD and ALS and discuss their possible phenotypic alterations and neurotoxic mechanisms that may contribute to neurodegeneration in these diseases.

Clinical features and genetic characterization of two dizygotic twins with C9orf72 expansion

The objective of the study was to present a detailed clinical, genetic, and epigenetic characterization of 2 amyotrophic lateral sclerosis (ALS) concordant dizygotic twins. The described cases underwent clinical and paraclinical examinations according to the motor neuron disease protocol of our referral center. Mutation analysis of the major causative genes related to ALS was performed. The methylation profile of the CpG island located in the promoter region of C9orf72 and in the repeat region itself was investigated by bisulfite sequencing of C9orf72 expansion carriers. The described cases presented an overlapping phenotype. Genetic analysis revealed the presence of an abnormal (>50 repeats) G₄C₂-repeat expansion in C9orf72. Both the direct bisulfite sequencing-sensitive and the methylation-sensitive HhaI assays did not reveal any DNA methylation at the CpG island 5' of the G₄C₂ repeat in C9orf72. The (G₄C₂)_n methylation assay indicated that also the expansion itself was not methylated in both twins, suggesting a probably intermediate allele expansion. This is the first report of ALS-concordant dizygotic twins carrying a C9orf72 expansion probably of intermediate length, and with a detailed clinical and genetic characterization. Twin studies add significant information about the mechanisms of C9orf72 expansion pleiotropism, probably driven by genetic, epigenetic, and environmental factors.

Clinical spectrum of C9orf72 expansion in a cohort of Huntington's disease phenocopies

The expansion in the C9orf72 gene has been recently reported as a genetic cause of Huntington's disease (HD) phenocopies. We aim to assess the frequency of the C9orf72 gene expansion in a Portuguese HD phenocopies cohort. Twenty HD phenotype-like patients without diagnosis were identified in our institutional database. C9orf72 gene expansion was detected using repeat-primed PCR. Clinical files were reviewed to characterize the phenotype of expansion-positive cases. One patient (5%) was positive for the C9orf72 expansion. A second patient presented 27 repeats-within the intermediate size interval. Both had familial neuropsychiatric disease characterized by diverse movement disorders, dementia, and psychiatric dysfunction that was distinct in severity and clinical expression. C9orf72 disease is clinically heterogeneous and without evident imaging markers. The definition of the role of intermediate alleles and of the pathological threshold for C9orf72 repeat expansions may have diagnostic implications.

The neural correlates and clinical characteristics of psychosis in the frontotemporal dementia continuum and the C9orf72 expansion

OBJECTIVE

This present study aims to address the gap in the literature regarding the severity and underlying neural correlates of psychotic symptoms in frontotemporal dementia with and without the C9orf72 gene expansion.

METHODS

Fifty-six patients with behavioural variant frontotemporal dementia (20 with concomitant amyotrophic lateral sclerosis) and 23 healthy controls underwent neuropsychological assessments, detailed clinical interview for assessment of psychosis symptoms, brain MRI and genetic testing. Carers underwent a clinical interview based upon the neuropsychiatric inventory. Patients were assessed at ForeFront, the Frontotemporal Dementia Research Group at Neuroscience Research Australia or at the Brain and Mind Centre, between January 2008 and December 2013. An index of psychosis was calculated, taking into account the degree and severity of psychosis in each case. Voxel-based morphometry analyses were used to explore relationships between the psychosis index and grey matter changes.

RESULTS

Thirty-four percent of frontotemporal dementia patients showed psychotic features. C9orf72 expansion cases were more likely to exhibit psychotic symptoms than non-carriers (64% vs. 26%; p = 0.006), which were also more severe (psychotic index 23.1 vs. 8.1; p = 0.002). Delusions comprised persecutory, somatic, jealous and grandiose types and were present in 57% of C9orf72 carriers and 19% of non-carriers (p = 0.006). Auditory, visual or tactile hallucinations were present in 36% of C9orf72 carriers and 17% of non-carriers (p = 0.13). Increased psychotic symptoms in C9orf72 expansion carriers correlated with atrophy in a distributed cortical and subcortical network that included discrete regions of the frontal, temporal and occipital cortices, as well as the thalamus, striatum and cerebellum.

CONCLUSIONS

This study underlines the need to consider and assess for psychotic symptoms in the frontotemporal dementia-amyotrophic lateral sclerosis continuum particularly in those with C9orf72 gene expansions. The network of brain regions identified in this study is strikingly similar to that identified in other psychotic disorders such as schizophrenia, which suggests that treatment strategies in psychiatry may be beneficial for the management of psychotic symptoms in frontotemporal dementia.

A PCR-based protocol to accurately size C9orf72 intermediate-length alleles

Although large expansions of the non-coding GGGGCC repeat in C9orf72 gene are clearly defined as pathogenic for Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD), intermediate-length expansions have also been associated with those and other neurodegenerative diseases. Intermediate-length allele sizing is complicated by intrinsic properties of current PCR-based methodologies, in that somatic mosaicism could be suspected. We designed a protocol that allows the exact sizing of intermediate-length alleles, as well as the identification of large expansions.

Identification of miRNAs as Potential Biomarkers in Cerebrospinal Fluid from Amyotrophic Lateral Sclerosis Patients

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disorder. Since no diagnostic laboratory test exists, the identification of specific biomarkers could be fundamental in clinical practice. microRNAs (miRNAs) are considered promising biomarkers for neurodegenerative diseases. The aim of the study was to identify a CSF miRNA set that could differentiate ALS from non-ALS condition. miRNA profiling in CSF from ALS patients (n = 24; eight with C9orf72 expansion) and unaffected control subjects (n = 24) by quantitative reverse transcription PCR identified fourteen deregulated miRNAs. Validation experiments confirmed eight miRNAs as significantly deregulated in ALS. No significant differences were observed between ALS patients with or without C9orf72 expansion. The receiver operator characteristic (ROC) curve analyses revealed the highest diagnostic accuracy for the upregulated miR181a-5p and the downregulated miR21-5p and miR15b-5p. The miR181a-5p/miR21-5p and miR181a-5p/miR15b-5p ratios detected ALS with 90 and 85 % sensitivity and 87 and 91 % specificity, respectively, confirming the application potential as disease biomarkers. These deregulated miRNAs are implicated in apoptotic way and provide insight into processes responsible for motor neuron degeneration.

GBA-associated parkinsonism and dementia: beyond α-synucleinopathies?

BACKGROUND AND PURPOSE

To date the role of GBA mutations beyond α-synucleinopathies in the parkinsonism-dementia spectrum is still unclear. The aim of the study was to screen for GBA mutations in progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), primary progressive aphasia (PPA) and the behavioural variant of frontotemporal dementia (bvFTD).

METHODS

In all, 303 patients with a clinical diagnosis of PSP (n = 157), CBS (n = 39), PPA (n = 35) and bvFTD (n = 72) and 587 neurologically healthy controls were screened for the most common GBA mutations.

RESULTS

GBA mutations were detected in one healthy control and four patients with a clinical diagnosis of PSP (n = 1), probable CBS (n = 2) and PPA (n = 1, with concomitant C9orf72 expansion). Overall the prevalence of GBA mutations was low in non-α-synucleinopathies but significantly higher in the CBS subgroup compared to controls.

CONCLUSION

Although numbers are small, our findings indicate that the clinical phenotype of GBA-associated neurodegenerative disease is more heterogeneous than previously assumed, including phenotypes not usually associated with underlying α-synucleinopathies. This may be of relevance, once causal therapeutic strategies for GBA-associated neurodegenerative disease are developed.