Contribution of ATXN2 intermediary polyQ expansions in a spectrum of neurodegenerative disorders

OBJECTIVE

The aim of this study was to establish the frequency of ATXN2 polyglutamine (polyQ) expansion in large cohorts of patients with amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and progressive supranuclear palsy (PSP), and to evaluate whether ATXN2 could act as a modifier gene in patients carrying the C9orf72 expansion.

METHODS

We screened a large cohort of French patients (1,144 ALS, 203 FTD, 168 FTD-ALS, and 109 PSP) for ATXN2 CAG repeat length. We included in our cohort 322 carriers of the C9orf72 expansion (202 ALS, 63 FTD, and 57 FTD-ALS).

RESULTS

We found a significant association with intermediate repeat size (≥29 CAG) in patients with ALS (both familial and sporadic) and, for the first time, in patients with familial FTD-ALS. Of interest, we found the co-occurrence of pathogenic C9orf72 expansion in 23.2% of ATXN2 intermediate-repeat carriers, all in the FTD-ALS and familial ALS subgroups. In the cohort of C9orf72 carriers, 3.1% of patients also carried an intermediate ATXN2 repeat length. ATXN2 repeat lengths in patients with PSP and FTD were found to be similar to the controls.

CONCLUSIONS

ATXN2 intermediary repeat length is a strong risk factor for ALS and FTD-ALS. Furthermore, we propose that ATXN2 polyQ expansions could act as a strong modifier of the FTD phenotype in the presence of a C9orf72 repeat expansion, leading to the development of clinical signs featuring both FTD and ALS.

Genetic analysis of SS18L1 in French amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating motor neuron disease including about 15% of genetically determined forms. A de novo mutation in the SS18L1 (also known as CREST or KIAA0693) gene encoding the calcium-responsive transactivator and/or neuronal chromatin remodeling complex subunit has recently been identified by exome sequencing of 47 sporadic ALS trios. This Q388stop mutation deleting the last 9 amino acids was shown to impair activity-dependent dendritic outgrowth. A missense mutation (c.369T>G, p.Ileu123Met) was also found in 1 of 62 ALS families previously screened for other ALS-related genes and not carrying any mutation. To confirm the contribution of SS18L1 to ALS, we sequenced the 11 coding exons and exon-intron boundaries in 87 familial ALS (FALS). We identified 2 variants: the c.660_668del, p.Gln222_Ser224del in a patient devoid of mutation in any ALS related genes and the c.790G>A, p.Ala264Thr in a patient carrying a p.Arg96Leu variant in the OPTN gene. As these variants were not found in Single Nucleotide Polymorphism databases and were absent from 180 controls they could be new SS18L1 mutations causing ALS.

Plasma peptide biomarker discovery for amyotrophic lateral sclerosis by MALDI-TOF mass spectrometry profiling

The diagnostic of Amyotrophic lateral sclerosis (ALS) remains based on clinical and neurophysiological observations. The actual delay between the onset of the symptoms and diagnosis is about 1 year, preventing early inclusion of patients into clinical trials and early care of the disease. Therefore, finding biomarkers with high sensitivity and specificity remains urgent. In our study, we looked for peptide biomarkers in plasma samples using reverse phase magnetic beads (C18 and C8) and MALDI-TOF mass spectrometry analysis. From a set of ALS patients (n=30) and healthy age-matched controls (n=30), C18- or C8-SVM-based models for ALS diagnostic were constructed on the base of the minimum of the most discriminant peaks. These two SVM-based models end up in excellent separations between the 2 groups of patients (recognition capability overall classes > 97%) and classify blinded samples (10 ALS and 10 healthy age-matched controls) with very high sensitivities and specificities (>90%). Some of these discriminant peaks have been identified by Mass Spectrometry (MS) analyses and correspond to (or are fragments of) major plasma proteins, partly linked to the blood coagulation.

C9ORF72 repeat expansions in the frontotemporal dementias spectrum of diseases: a flow-chart for genetic testing

Frontotemporal dementia (FTD) refers to a disease spectrum including the behavioral variant FTD (bvFTD), primary progressive aphasia (PPA), progressive supranuclear palsy/corticobasal degeneration syndrome (PSP/CBDS), and FTD with amyotrophic lateral sclerosis (FTD-ALS). A GGGGCC expansion in C9ORF72 is a major cause of FTD and ALS. C9ORF72 was analyzed in 833 bvFTD, FTD-ALS, PPA, and PSP/CBDS probands; 202 patients from 151 families carried an expansion. C9ORF72 expansions were much more frequent in the large subgroup of patients with familial FTD-ALS (65.9%) than in those with pure FTD (12.8%); they were even more frequent than in familial pure ALS, according to estimated frequencies in the literature (23-50%). The frequency of carriers in non-familial FTD-ALS (12.7%) indicates that C9ORF72 should be analyzed even when family history is negative. Mutations were detected in 6.8% of PPA patients, and in 3.2% of patients with a clinical phenotype of PSP, thus enlarging the phenotype spectrum of C9ORF72. Onset was later in C9ORF72 (57.4 years, 95%CI: 55.9-56.1) than in MAPT patients (46.8, 95%CI: 43.0-50.6; p = 0.00001) and the same as in PGRN patients (59.6 years; 95%CI: 57.6-61.7; p = 0.4). ALS was more frequent in C9ORF72 than in MAPT and PGRN patients; onset before age 50 and parkinsonism were indicative of MAPT mutations, whereas hallucinations were indicative of PGRN mutations; prioritization of genetic testing is thus possible. Penetrance was age- and gender-dependent: by age 50, 78% of male carriers were symptomatic, but only 52% of females. This can also guide genetic testing and counseling. A flowchart for genetic testing is thus proposed.

Muscle histone deacetylase 4 upregulation in amyotrophic lateral sclerosis: potential role in reinnervation ability and disease progression

Amyotrophic lateral sclerosis is a typically rapidly progressive neurodegenerative disorder affecting motor neurons leading to progressive muscle paralysis and death, usually from respiratory failure, in 3-5 years. Some patients have slow disease progression and prolonged survival, but the underlying mechanisms remain poorly understood. Riluzole, the only approved treatment, only modestly prolongs survival and has no effect on muscle function. In the early phase of the disease, motor neuron loss is initially compensated for by collateral reinnervation, but over time this compensation fails, leading to progressive muscle wasting. The crucial role of muscle histone deacetylase 4 and its regulator microRNA-206 in compensatory reinnervation and disease progression was recently suggested in a mouse model of amyotrophic lateral sclerosis (transgenic mice carrying human mutations in the superoxide dismutase gene). Here, we sought to investigate whether the microRNA-206-histone deacetylase 4 pathway plays a role in muscle compensatory reinnervation in patients with amyotrophic lateral sclerosis and thus contributes to disease outcome differences. We studied muscle reinnervation using high-resolution confocal imaging of neuromuscular junctions in muscle samples obtained from 11 patients with amyotrophic lateral sclerosis, including five long-term survivors. We showed that the proportion of reinnervated neuromuscular junctions was significantly higher in long-term survivors than in patients with rapidly progressive disease. We analysed the expression of muscle candidate genes involved in the reinnervation process and showed that histone deacetylase 4 upregulation was significantly greater in patients with rapidly progressive disease and was negatively correlated with the extent of muscle reinnervation and functional outcome. Conversely, the proposed regulator of histone deacetylase 4, microRNA-206, was upregulated in both patient groups, but did not correlate with disease progression or reinnervation. We conclude that muscle expression of histone deacetylase 4 may be a key factor for muscle reinnervation and disease progression in patients with amyotrophic lateral sclerosis. Specific histone deacetylase 4 inhibitors may then constitute a therapeutic approach to enhancing motor performance and slowing disease progression in amyotrophic lateral sclerosis.

A rare motor neuron deleterious missense mutation in the DPYSL3 (CRMP4) gene is associated with ALS

The dihydropyrimidinase-like 3 (DPYSL3) or Collapsin Response Mediator Protein 4a (CRMP4a) expression is modified in neurodegeneration and is involved in several ALS-associated pathways including axonal transport, glutamate excitotoxicity, and oxidative stress. The objective of the study was to analyze CRMP4 as a risk factor for ALS. We analyzed the DPYSL3/CRMP4 gene in French ALS patients (n = 468) and matched-controls (n = 394). We subsequently examined a variant in a Swedish population (184 SALS, 186 controls), and evaluated its functional effects on axonal growth and survival in motor neuron cell culture. The rs147541241:A>G missense mutation occurred in higher frequency among French ALS patients (odds ratio = 2.99) but the association was not confirmed in the Swedish population. In vitro expression of mutated DPYSL3 in motor neurons reduced axonal growth and accelerated cell death compared with wild type protein. Thus, the association between the rs147541241 variant and ALS was limited to the French population, highlighting the geographic particularities of genetic influences (risks, contributors). The identified variant appears to shorten motor neuron survival through a detrimental effect on axonal growth and CRMP4 could act as a key unifier in transduction pathways leading to neurodegeneration through effects on early axon development.

Mutations in SQSTM1 encoding p62 in amyotrophic lateral sclerosis: genetics and neuropathology

Mutations in SQSTM1 encoding the sequestosome 1/p62 protein have recently been identified in familial and sporadic cases of amyotrophic lateral sclerosis (ALS). p62 is a component of the ubiquitin inclusions detected in degenerating neurons in ALS patients. We sequenced SQSTM1 in 90 French patients with familial ALS (FALS) and 74 autopsied ALS cases with sporadic ALS (SALS). We identified, at the heterozygote state, one missense c.1175C>T, p.Pro392Leu (exon 8) in one of our FALS and one substitution in intron 7 (the c.1165+1G>A, previously called IVS7+1 G-A, A390X) affecting the exon 7 splicing site in one SALS. These mutations that are located in the ubiquitin-associated domain (UBA domain) of the p62 protein have already been described in Paget's disease and ALS patients carrying these mutations had both concomitant Paget's disease. However, we also identified two novel missense mutations in two SALS: the c.259A>G, p.Met87Val in exon 2 and the c.304A>G, p.Lys102Glu in exon 3. These mutations that were not detected in 360 control subjects are possibly pathogenic. Neuropathology analysis of three patients carrying SQSTM1 variants revealed the presence of large round p62 inclusions in motor neurons, and immunoblot analysis showed an increased p62 and TDP-43 protein levels in the spinal cord. Our results confirm that SQSTM1 gene mutations could be the cause or genetic susceptibility factor of ALS in some patients.

Validation of robust tools to measure sialorrhea in amyotrophic lateral sclerosis: a study in a large French cohort

There is an unmet need for validated tools to measure sialorrhea in amyotrophic lateral sclerosis, especially to evaluate treatments. We assessed the inter-/intra-rate reviewer reliability of two scales: the Oral Secretion Scale (OSS), specifically developed for ALS patients, and the Sialorrhea Scoring Scale (SSS), initially developed for Parkinson's disease patients. Sialorrhea was rated in 69 ALS consecutive patients by four evaluators: two neurologists, one nurse and one speech therapist. Inter-rater reliability was evaluated by the light kappa coefficient and intra-rater reliability by the weighted kappa coefficient. We also compared patients' and caregivers' answers. Results demonstrated that the two scales present a high inter-/intra-rater reliability: weighted kappas were 0.85 for both scales and light kappas 0.89 for the OSS and 0.88 for the SSS. Both scales also showed a good intra-profession reliability (OSS kappa = 0.84; SSS kappa = 0.79) and agreement between patients' and caregivers' answers. The SSS showed a higher responsiveness compared to OSS. In conclusion, both Oral Secretion Scale and Sialorrhea Scoring Scale are reliable tools to measure sialorrhea in ALS patients. Because of the wide range of salivation degrees, SSS may be more sensitive as a tool to evaluate treatments in patients with severe hypersialorrhea.

Phenotype difference between ALS patients with expanded repeats in C9ORF72 and patients with mutations in other ALS-related genes

BACKGROUND

Expanded GGGGCC hexanucleotide repeats in the promoter of the C9ORF72 gene have recently been identified in frontotemporal dementia (FTD), Amyotrophic Lateral Sclerosis (ALS) and ALS-FTD and appear as the most common genetic cause of familial (FALS) and sporadic (SALS) forms of ALS.

METHODS

We searched for the C9ORF72 repeat expansion in 950 French ALS patients (225 FALS and 725 SALS) and 580 control subjects and performed genotype-phenotype correlations.

RESULTS

The repeat expansion was present in 46% of FALS, 8% of SALS and 0% of controls. Phenotype comparisons were made between FALS patients with expanded C9ORF72 repeats and patients carrying another ALS-related gene (SOD1, TARDBP, FUS) or a yet unidentified genetic defect. SALS patients with and without C9ORF72 repeat expansions were also compared. The C9ORF72 group presented more frequent bulbar onset both in FALS (p<0.0001 vs SOD1, p=0.002 vs TARDBP, p=0.011 vs FUS, p=0.0153 vs other FALS) and SALS (p=0.047). FALS patients with C9ORF72 expansions had more frequent association with FTD than the other FALS patients (p<0.0001 vs SOD1, p=0.04 vs TARDBP, p=0.004 vs FUS, p=0.03 vs other FALS). C9ORF72-linked FALS patients presented an older age of onset than SOD1 (p=0.0139) or FUS mutation (p<0.0001) carriers. Disease duration was shorter for C9ORF72 expansion carriers than for SOD1 (p<0.0001) and TARDBP (p=0.0242) carriers, other FALS (p<0.0001) and C9ORF72-negative SALS (p=0.0006).

CONCLUSIONS

Our results confirm the major role of expanded repeats in C9ORF72 as causative for ALS and provide evidence for specific phenotypic aspects compared to patients with other ALS-related genes.

Genotype-phenotype relationship in 2 SMA III patients with novel mutations in the Tudor domain

OBJECTIVE

We report the cases of 2 patients with late-onset spinal muscular atrophy (SMA) type III, who were hemizygous for SMN1 deletion and carriers of novel SMN1 intragenic missense mutations, and we investigate the genotype-phenotype relationship.

METHODS

Patients were tested for SMN1 deletions with standard methodology. Sequencing of all exons, exon-intron junctions, and flanking sequences of SMN1 by nested PCR was used to detect intragenic point mutations. SMN1 and SMN2 quantification was undertaken to investigate the genotype-phenotype relationship.

RESULTS

Two novel point mutations were identified in exon 3 of SMN1 (p.Tyr130Cys and p.Tyr130His) in the highly conserved Tudor domain of the Smn protein.

CONCLUSIONS

The genetic basis of SMA in the rare cases of compound heterozygous carriers of SMN1 deletions is complex. Small intragenic SMN1 mutations often lead to severe SMA phenotypes, especially if the point mutations lie in exon 3 that codes for the highly conserved Tudor domain of the Smn protein. Although both our patients were carriers of intragenic SMN1 mutations in the coding region of the Tudor domain, they presented with a mild SMA phenotype despite a low SMN2 copy number. We discuss the possible determinant role of these novel missense mutations in the phenotypic outcome and compensatory mechanisms that may account for the genotype-phenotype discrepancy.

Abnormalities of satellite cells function in amyotrophic lateral sclerosis

Abstract Amyotrophic lateral sclerosis (ALS) is characterized by progressive denervation leading to muscle atrophy prevented, during the early phase, by compensatory reinnervation. Little is known about muscle fibre regeneration capacity in ALS. We have carried out in vivo and in vitro investigation of skeletal muscle in ALS. Seven ALS patients underwent a deltoid muscle biopsy. Immunohistochemical analysis revealed various degrees of denervation- and reinnervation-related changes in the ALS muscle biopsies including satellite cells (SCs) activation and regenerating fibres. Only 3/7 primary cultures of ALS muscle cells were successfully established and had sufficient myogenicity, as assessed by desmin positivity, to be used without further purification. This was in contrast with the cultures derived from control muscles, predominantly desmin-positive cells. Although capable to proliferate in vitro, ALS-derived SCs presented an abnormal senescent-like morphology. Markers of senescence, including senescent-associated (SA)-βGal activity and p16 expression, were increased. Furthermore, ALS-derived SCs were also unable to fully differentiate in vitro as shown by abnormal myotubes morphology and reduced MHC isoform expression, compared to control myotubes. Our study suggests that SC function is altered in ALS. This could limit the efficacy of compensatory processes and therefore could contribute to the progression of muscle atrophy and weakness.

Identification of novel FUS mutations in sporadic cases of amyotrophic lateral sclerosis

Mutations in the FUS gene have been recently associated with amyotrophic lateral sclerosis (ALS). While most of the variants have been identified in patients with a family history of the disease, a few mutations were also found in sporadic patients. Considering this, we wanted to evaluate the frequency of mutations in the coding region of the FUS gene in a sporadic ALS (SALS) cohort compared to a control population. We tested 475 SALS cases of European origin and 475 matched controls for coding variations in the 15 exons of the FUS gene. Rare novel variants were identified in a total of five SALS patients: one missense, one deletion, one frameshift, and one nonsense substitution. Two of the four variants are located in the carboxy terminal of the protein where the previously reported variants were mostly clustered. In conclusion, FUS gene mutations are rare in SALS, with four new FUS variants identified in five different SALS cases. These findings will help evaluate the proportion of FUS variations in the SALS population, and to better understand its contributing role to ALS pathology.