ATAXIN2 CAG-repeat length in Italian patients with amyotrophic lateral sclerosis: risk factor or variant phenotype? Implication for genetic testing and counseling

TDP-43 levels in the brain tissue of ALS cases with and without C9ORF72 or ATXN2 gene expansions

OBJECTIVE

To assess the amount of phosphorylated and nonphosphorylated TAR DNA-binding protein 43 (TDP-43) in the motor brain regions of cases of amyotrophic lateral sclerosis (ALS) with and without repeat expansions in the ATXN2 or C9ORF72 genes.

METHODS

The 45-kDa phosphorylated form of TDP-43 and 43-kDa nonphosphorylated form of TDP-43 were quantified by immunoblot in postmortem brain tissue from the motor cortex, spinal cord, and cerebellar vermis of 23 cases with ALS with repeat expansions in the ATXN2 or C9ORF72 genes and sporadic disease and 10 controls.

RESULTS

Significantly greater levels of phosphorylated TDP-43 were identified in the motor cortex of cases with ALS with C9ORF72 expansions, and significantly greater amounts of phosphorylated TDP-43 were found in the spinal cord of cases with ALS with intermediate ATXN2 expansions. In contrast, however, similar levels of nonphosphorylated TDP-43 were found in all 3 regions between ALS groups.

CONCLUSION

Despite its central role in the pathogenesis of ALS and the emergence of potential targets to modify its aggregation, TDP-43 levels have not been quantified in pathologically confirmed cases with ALS. The present results demonstrating significant differences in phosphorylated but not nonphosphorylated TDP-43 levels suggest that different posttranslational modifications are involved in the generation of greater pathologic TDP-43 levels identified here in our cohort of cases with genetic expansions. These findings are consistent with emerging studies implicating distinct pathomechanisms in the generation of pathologic TDP-43 in cases with ALS with C9ORF72 or ATXN2 expansions and are of relevance to therapeutic research aimed at reducing pathologic TDP-43 in all or a subset of patients with ALS.

Association of ATXN2 intermediate-length CAG repeats with amyotrophic lateral sclerosis correlates with the distributions of normal CAG repeat alleles among individual ethnic populations

Intermediate-length CAG repeats in ATXN2 have been widely shown to be a risk factor for sporadic amyotrophic lateral sclerosis (SALS). To evaluate the association of ATXN2 intermediate-length CAG repeat alleles with an increased risk of SALS, we investigated distributions of CAG repeat alleles in 394 patients with SALS and 490 control individuals in the Japanese population. In the intermediate-length repeat units of 29 or more, we identified one SALS patient with 31 repeat units and two control individuals with 30 repeat units. Thus, no significant differences in the carrier frequency of intermediate-length CAG repeat alleles were detected between patients with SALS and control individuals. When we investigated the distribution of "large normal alleles" defined as ATXN2 CAG repeats ranging from 24 up to 33 in the Japanese population compared with those in other populations in previous studies, the frequency of large normal alleles was significantly higher in the European and North American series than in the Japanese series. Moreover, these frequencies in the Turkish, Chinese, Korean, and Brazilian (Latin American) series were also higher than that in the Japanese series. These results raise the possibility that the frequencies of large normal alleles in individual populations underlie the frequencies of ALS risk alleles in the corresponding populations.

Tremor in motor neuron disease may be central rather than peripheral in origin

BACKGROUND AND PURPOSE

Motor neuron disease (MND) refers to a spectrum of degenerative diseases affecting motor neurons. Recent clinical and post-mortem observations have revealed considerable variability in the phenotype. Rhythmic involuntary oscillations of the hands during action, resembling tremor, can occur in MND, but their pathophysiology has not yet been investigated.

METHODS

A total of 120 consecutive patients with MND were screened for tremor. Twelve patients with action tremor and no other movement disorders were found. Ten took part in the study. Tremor was recorded bilaterally using surface electromyography (EMG) and triaxial accelerometer, with and without a variable weight load. Power spectra of rectified EMG and accelerometric signal were calculated. To investigate a possible cerebellar involvement, eyeblink classic conditioning was performed in five patients.

RESULTS

Action tremor was present in about 10% of our population. All patients showed distal postural tremor of low amplitude and constant frequency, bilateral with a small degree of asymmetry. Two also showed simple kinetic tremor. A peak at the EMG and accelerometric recordings ranging from 4 to 12 Hz was found in all patients. Loading did not change peak frequency in either the electromyographic or accelerometric power spectra. Compared with healthy volunteers, patients had a smaller number of conditioned responses during eyeblink classic conditioning.

CONCLUSIONS

Our data suggest that patients with MND can present with action tremor of a central origin, possibly due to a cerebellar dysfunction. This evidence supports the novel idea of MND as a multisystem neurodegenerative disease and that action tremor can be part of this condition.

The epidemiology and genetics of Amyotrophic lateral sclerosis in China

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder associated with loss of motor neurons. Previous knowledge of the disease has been mainly based on studies from Caucasian ALS patients of European descent. Here we review the epidemiological characteristics of ALS among the Chinese population in order to compare the similarities and differences between Chinese ALS cases and those from other countries. We describe a potential lower incidence and prevalence of ALS, a younger age of onset and a lower proportion of familial ALS cases in the Chinese population. Additionally, we highlight potential genetic differences between Chinese and Caucasian ALS patients. Most notably, the frequency of GGGGCC repeat expansions in C9ORF72 in Chinese ALS is significantly lower than in Caucasians. Since some conclusions might not be consistent across all of the studies around China to date, we suggest that it is necessary to carry out a prospective population-based study and large-scale gene sequencing around to better define epidemiological and genetic features of Chinese ALS patients.

C9orf72 hexanucleotide repeat expansions and Ataxin 2 intermediate length repeat expansions in Indian patients with amyotrophic lateral sclerosis

Repeat expansions in the chromosome 9 open reading frame 72 (C9orf72) gene have been recognized as a major contributor to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia in the Caucasian population. Intermediate length repeat expansions of CAG (polyQ) repeat in the ATXN2 gene have also been reported to increase the risk of developing ALS in North America and Europe. We screened 131 ALS patients and 127 healthy controls from India for C9orf72 and ATXN2 repeat expansions. We found pathogenic hexanucleotide expansions in 3 of the 127 sporadic ALS patients, in 1 of the 4 familial ALS patients, and in none of the healthy controls. In addition, our findings suggest that the 10 base-pair deletion that masks detection of C9orf72 repeat expansion does not explain the low frequency of this repeat expansion among Indian ALS patients. Intermediate length polyQ expansions (27Qs-32Qs) in the ATXN2 gene were detected in 6 of the 127 sporadic ALS patients and 2 of the 127 of the healthy controls. Long ATXN2 polyQ repeats (≥33Qs) were not present in any of the ALS patients or controls. Our findings highlight the need for large-scale multicenter studies on Indian ALS patients to better understand the underlying genetic causes.

ATXN2 trinucleotide repeat length correlates with risk of ALS

We investigated a CAG trinucleotide repeat expansion in the ATXN2 gene in amyotrophic lateral sclerosis (ALS). Two new case-control studies, a British dataset of 1474 ALS cases and 567 controls, and a Dutch dataset of 1328 ALS cases and 691 controls were analyzed. In addition, to increase power, we systematically searched PubMed for case-control studies published after 1 August 2010 that investigated the association between ATXN2 intermediate repeats and ALS. We conducted a meta-analysis of the new and existing studies for the relative risks of ATXN2 intermediate repeat alleles of between 24 and 34 CAG trinucleotide repeats and ALS. There was an overall increased risk of ALS for those carrying intermediate sized trinucleotide repeat alleles (odds ratio 3.06 [95% confidence interval 2.37-3.94]; p = 6 × 10-18), with an exponential relationship between repeat length and ALS risk for alleles of 29-32 repeats (R2 = 0.91, p = 0.0002). No relationship was seen for repeat length and age of onset or survival. In contrast to trinucleotide repeat diseases, intermediate ATXN2 trinucleotide repeat expansion in ALS does not predict age of onset but does predict disease risk.

RNA-binding disturbances as a continuum from spinocerebellar ataxia type 2 to Parkinson disease

CAG triplet expansions in Ataxin-2 gene (ATXN2) cause spinocerebellar ataxia type 2 and have a role that remains to be clarified in Parkinson's disease (PD). To study the molecular events associated with these expansions, we sequenced them and analyzed the transcriptome from blood cells of controls and three patient groups diagnosed with spinocerebellar ataxia type 2 (herein referred to as SCA2c) or PD with or without ATXN2 triplet expansions (named SCA2p). The transcriptome profiles of these 40 patients revealed three main observations: i) a specific pattern of pathways related to cellular contacts, proliferation and differentiation associated with SCA2p group, ii) similarities between the SCA2p and sporadic PD groups in genes and pathways known to be altered in PD such as Wnt, Ephrin and Leukocyte extravasation signaling iii) RNA metabolism disturbances with "RNA-binding" and "poly(A) RNA-binding" as a common feature in all groups. Remarkably, disturbances of ALS signaling were shared between SCA2p and sporadic PD suggesting common molecular dysfunctions in PD and ALS including CACNA1, hnRNP, DDX and PABPC gene family perturbations. Interestingly, the transcriptome profiles of patients with parkinsonian phenotypes were prevalently associated with alterations of translation while SCA2c and PD patients presented perturbations of splicing. While ATXN2 RNA expression was not perturbed, its protein expression in immortalized lymphoblastoid cells was significantly decreased in SCA2c and SCA2p versus control groups assuming post-transcriptional biological perturbations. In conclusion, the transcriptome data do not exclude the role of ATXN2 mutated alleles in PD but its decrease protein expression in both SCA2c and SCA2p patients suggest a potential involvement of this gene in PD. The perturbations of "RNA-binding" and "poly(A) RNA-binding" molecular functions in the three patient groups as well as gene deregulations of factors not yet described in PD but known to be deleterious in other neurological conditions, suggest the existence of RNA-binding disturbances as a continuum between spinocerebellar ataxia type 2 and Parkinson's disease.

Drosophila as an In Vivo Model for Human Neurodegenerative Disease

With the increase in the ageing population, neurodegenerative disease is devastating to families and poses a huge burden on society. The brain and spinal cord are extraordinarily complex: they consist of a highly organized network of neuronal and support cells that communicate in a highly specialized manner. One approach to tackling problems of such complexity is to address the scientific questions in simpler, yet analogous, systems. The fruit fly, Drosophila melanogaster, has been proven tremendously valuable as a model organism, enabling many major discoveries in neuroscientific disease research. The plethora of genetic tools available in Drosophila allows for exquisite targeted manipulation of the genome. Due to its relatively short lifespan, complex questions of brain function can be addressed more rapidly than in other model organisms, such as the mouse. Here we discuss features of the fly as a model for human neurodegenerative disease. There are many distinct fly models for a range of neurodegenerative diseases; we focus on select studies from models of polyglutamine disease and amyotrophic lateral sclerosis that illustrate the type and range of insights that can be gleaned. In discussion of these models, we underscore strengths of the fly in providing understanding into mechanisms and pathways, as a foundation for translational and therapeutic research.

Amyotrophic lateral sclerosis risk for spinocerebellar ataxia type 2 ATXN2 CAG repeat alleles: a meta-analysis

IMPORTANCE

Repeats of CAG in the ataxin 2 gene (ATXN2) in the long-normal range (sometimes referred to as intermediate) have been identified as modifiers of amyotrophic lateral sclerosis (ALS) risk. Prior studies have used thresholding considering various cutoffs for ATXN2 repeat length.

OBJECTIVE

To calculate association between ATXN2 CAG repeat alleles and increased risk of ALS across multiple ethnic groups.

DATA SOURCES

The MEDLINE database was searched for studies published by December 29, 2013, reporting ATXN2 CAG repeat length in patients with ALS and controls.

STUDY SELECTION

Studies were included if they reported original data on relative risks or odds ratios (ORs) from ALS and control populations for individual ATXN2 alleles. Review articles that reported no new data were not included in the analysis.

DATA EXTRACTION AND SYNTHESIS

Analysis of allele distribution was performed to ensure that all studies followed identical allele sizing. The ORs, 95% confidence intervals, and population attributable risk percentages were calculated according to standard procedures.

MAIN OUTCOMES AND MEASURES

Occurrence of ALS associated with ATXN2 repeat alleles, expressed as ORs.

RESULTS

Nine studies were analyzed, including 7505 controls and 6151 sporadic ALS cases. The ALS and control cohorts were recruited from different geographical and ethnic regions including the United States, French Canada/Canada, Belgium and the Netherlands, Germany, Italy, mainland China, Turkey, and Flanders-Belgium. The ATXN2 CAG repeat lengths ranged from 13 to 39 in patients with ALS and from 13 to 34 in controls. The ORs were less than 1.00 for alleles with 25 to 28 repeats. The OR was 1.55 for 30 repeats, but this elevation was not statistically significant (95% CI, 0.88-2.73). The ORs were 2.70 (95% CI, 1.47-4.93) for 31 CAG repeats, 11.09 (95% CI, 4.16-29.57) for 32 repeats, and 5.76 (95% CI, 1.79-18.57) for 33 repeats.

CONCLUSIONS AND RELEVANCE

In contrast to prior studies with smaller numbers, risk for ALS associated with long-normal alleles is complex. Alleles with 27 and 28 repeats lower ALS risk slightly. The risk for ALS increases beginning with 29 repeats and reaches a maximum at 32 and 33 repeats. Of note, alleles with repeats of these lengths are known to be predisposed to meiotic expansion to full-penetrance mutant alleles. In patients with ALS, alleles with 31 to 33 repeats may have undergone preferential expansion in motor neurons during mitosis or DNA repair. Our meta-analysis provides a framework for counseling individuals with long-normal ATXN2 repeats.

Intermediate CAG repeat expansion in the ATXN2 gene is a unique genetic risk factor for ALS--a systematic review and meta-analysis of observational studies

Amyotrophic lateral sclerosis (ALS) is a rare degenerative condition of the motor neurons. Over 10% of ALS cases are linked to monogenic mutations, with the remainder thought to be due to other risk factors, including environmental factors, genetic polymorphisms, and possibly gene-environmental interactions. We examined the association between ALS and an intermediate CAG repeat expansion in the ATXN2 gene using a meta-analytic approach. Observational studies were searched with relevant disease and gene terms from MEDLINE, EMBASE, and PsycINFO from January 2010 through to January 2014. All identified articles were screened using disease terms, gene terms, population information, and CAG repeat information according to PRISMA guidelines. The final list of 17 articles was further evaluated based on the study location, time period, and authors to exclude multiple usage of the same study populations: 13 relevant articles were retained for this study. The range 30-33 CAG repeats in the ATXN2 gene was most strongly associated with ALS. The meta-analysis revealed that the presence of an intermediate CAG repeat (30-33) in the ATXN2 gene was associated with an increased risk of ALS [odds ratio (OR) = 4.44, 95%CI: 2.91-6.76)] in Caucasian ALS patients. There was no significant difference in the association of this CAG intermediate repeat expansion in the ATXN2 gene between familial ALS cases (OR = 3.59, 1.58-8.17) and sporadic ALS cases (OR = 3.16, 1.88-5.32). These results indicate that the presence of intermediate CAG repeat expansion in the ATXN2 gene is a specific genetic risk factor for ALS, unlike monogenic mutations with an autosomal dominant transmission mode, which cause a more severe phenotype of ALS, with a higher prevalence in familial ALS.

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.

Clinical neurogenetics: amyotrophic lateral sclerosis

Our understanding of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease, is expanding rapidly as its genetic causes are uncovered. The pace of new gene discovery over the last 5 years has accelerated, providing new insights into the pathogenesis of disease and highlighting biological pathways as targets for therapeutic development. This article reviews our current understanding of the heritability of ALS and provides an overview of each of the major ALS genes, highlighting their phenotypic characteristics and frequencies as a guide for clinicians evaluating patients with ALS.

Extensive molecular genetic survey of Taiwanese patients with amyotrophic lateral sclerosis

Identification of genetic mutations has been of burgeoning importance in amyotrophic lateral sclerosis (ALS) in recent years. The aim of this study was to determine the frequency and spectrum of mutations in major ALS-causing genes in a Taiwanese ALS cohort of Han Chinese origin. Mutational analyses of the SOD1, TARDBP, FUS, OPTN, VCP, UBQLN2, SQSTM1, PFN1, HNRNPA1, and HNRNPA2B1 genes were carried out by direct sequencing in 161 unrelated patients with ALS, including 30 with familial ALS (FALS) and 131 with sporadic ALS (SALS). The CAG repeat size in ATXN2 and the GGGGCC repeat expansion in C9ORF72 of the patients were also investigated. Mutations were identified in 33 patients (20.5%, 33/161), including 22 with FALS and 11 with SALS. Mutations were identified most frequently in SOD1 (7.5%). Three mutations are novel, including SOD1 p.G10A, SOD1 p.D83N, and OPTN p.L494W. These findings broaden the spectrum of ALS-causing mutations and are indispensable for designing optimal strategies of mutational analysis and genetic counseling of ALS for patients of Chinese origin.

Ataxin-2 as potential disease modifier in C9ORF72 expansion carriers

Repeat expansions in chromosome 9 open reading frame 72 (C9ORF72) are an important cause of both motor neuron disease (MND) and frontotemporal dementia (FTD). Currently, little is known about factors that could account for the phenotypic heterogeneity detected in C9ORF72 expansion carriers. In this study, we investigated 4 genes that could represent genetic modifiers: ataxin-2 (ATXN2), non-imprinted in Prader-Willi/Angelman syndrome 1 (NIPA1), survival motor neuron 1 (SMN1), and survival motor neuron 2 (SMN2). Assessment of these genes, in a unique cohort of 331 C9ORF72 expansion carriers and 376 control subjects, revealed that intermediate repeat lengths in ATXN2 possibly act as disease modifier in C9ORF72 expansion carriers; no evidence was provided for a potential role of NIPA1, SMN1, or SMN2. The effects of intermediate ATXN2 repeats were most profound in probands with MND or FTD/MND (2.1% vs. 0% in control subjects, p = 0.013), whereas the frequency in probands with FTD was identical to control subjects. Though intermediate ATXN2 repeats were already known to be associated with MND risk, previous reports did not focus on individuals with clear pathogenic mutations, such as repeat expansions in C9ORF72. Based on our present findings, we postulate that intermediate ATXN2 repeat lengths may render C9ORF72 expansion carriers more susceptible to the development of MND; further studies are needed, however, to validate our findings.

Amyotrophic lateral sclerosis and spinocerebellar ataxia type 2 in a family with full CAG repeat expansions of ATXN2

IMPORTANCE

A family with coexistence of spinocerebellar ataxia type 2 and amyotrophic lateral sclerosis (ALS) is described.

OBSERVATIONS

Intermediate or full CAG repeat expansions of ATXN2 are associated with ALS. However, no coexistence of spinocerebellar ataxia type 2 and ALS in a family has been reported in the literature.We describe a 47-year-old woman with an 11-year history of ataxia and her paternal uncle with ALS who were evaluated at Columbia University Medical Center since July 2006. Both our patient with ataxia and her uncle with ALS have full pathological CAG repeat expansions of ATXN2.

CONCLUSIONS AND RELEVANCE

The diverse clinical phenotypes of ATXN2 CAG expansions and their coexistence in a single family are highlighted. A clinician should consider the diagnosis of spinocerebellar ataxia type 2 when encountering a patient with ataxia and a family history of ALS.

Whole-blood global DNA methylation is increased in amyotrophic lateral sclerosis independently of age of onset

ALS is a heterogeneous disease that is not well understood. Epigenetic rearrangements are important in complex disorders including motor neuron diseases. The aim of this study was to determine whether whole-blood DNA methylation (DNA MET %) is a potential modifier of age at onset in ALS. DNA MET % was measured as incorporation of [(3)H]dCTP following HpaII cut in 96 ALS patients and 87 controls, comprising: early-onset (< 55 years of age) and late-onset (> 74 years of age). Methionine (Met) and homocysteine (Hcy) plasma levels were assessed by liquid chromatography selected reaction monitoring coupled with isotope-dilution mass spectrometry. Results showed that DNA MET % was increased in ALS patients independently of age of onset. Compared to the other three groups, Hcy plasma levels were reduced in early-onset ALS patients but Met levels were similar. ROC analysis reported Met levels and DNA MET %, respectively, with a slight and moderate discriminative power. In conclusion, increased DNA MET % is a possible marker of epigenetic dysfunction in ALS independently of age of onset. Further studies dissecting biological determinants of phenotypic complexity in ALS may help in developing successful therapeutic strategies.

De novo mutations in ataxin-2 gene and ALS risk

Pathogenic CAG repeat expansion in the ataxin-2 gene (ATXN2) is the genetic cause of spinocerebellar ataxia type 2 (SCA2). Recently, it has been associated with Parkinsonism and increased genetic risk for amyotrophic lateral sclerosis (ALS). Here we report the association of de novo mutations in ATXN2 with autosomal dominant ALS. These findings support our previous conjectures based on population studies on the role of large normal ATXN2 alleles as the source for new mutations being involved in neurodegenerative pathologies associated with CAG expansions. The de novo mutations expanded from ALS/SCA2 non-risk alleles as proven by meta-analysis method. The ALS risk was associated with SCA2 alleles as well as with intermediate CAG lengths in the ATXN2. Higher risk for ALS was associated with pathogenic CAG repeat as revealed by meta-analysis.

ATXN2 CAG repeat expansions increase the risk for Chinese patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with unclear etiology. Recently, intermediate CAG repeat expansions in ATXN2, the gene responsible for spinocerebellar ataxia type 2 (SCA2), have been identified as a possible genetic risk factor for ALS. In this study, we analyzed the ATXN2 CAG repeat length in Chinese patients with ALS to evaluate the relationship between the genotype and phenotype. We studied 1,067 patients with ALS and 506 controls from mainland China (excluding Tibet). We collected clinical data and analyzed fluorescent PCR products to assess ATXN2 CAG repeat length in all of the samples. We observed that intermediate CAG repeat expansions in ATXN2 (CAG repeat length >30) were associated with ALS (p = 0.004). There was no significant difference in clinical characteristics between the groups with and without intermediate CAG repeat expansions in ATXN2. Our data indicate that, for ALS patients from mainland China, intermediate CAG repeat expansions in ATXN2 increase the risk of ALS but have no effect on disease phenotype.