Spinocerebellar Ataxia Type 2 Is Associated with the Extracellular Loss of Superoxide Dismutase but Not Catalase Activity

BackgroundSpinocerebellar ataxia type 2 (SCA2) is an inherited and still incurable neurodegenerative disorder. Evidence suggests that pro-oxidant agents as well as factors involved in antioxidant cellular defenses are part of SCA2 physiopathology.AimTo assess the influence of superoxide dismutase (SOD3) and catalase (CAT) enzymatic activities on the SCA2 syndrome.MethodClinical, molecular, and electrophysiological variables, as well as SOD3 and CAT enzymatic activities were evaluated in 97 SCA2 patients and in 64 age- and sex-matched control individuals.ResultsSpinocerebellar ataxia type 2 patients had significantly lower SOD3 enzymatic activity than the control group. However, there were no differences between patients and controls for CAT enzymatic activity. The effect size for the loss of patients’ SOD3 enzymatic activity was 0.342, corresponding to a moderate effect. SOD3 and CAT enzymatic activities were not associated with the CAG repeat number at the ATXN2 gene. SOD3 and CAT enzymatic activities did not show significant associations with the age at onset, severity score, or the studied electrophysiological markers.ConclusionThere is a reduced SOD3 enzymatic activity in SCA2 patients with no repercussion on the clinical phenotype

Redox Imbalance Associates with Clinical Worsening in Spinocerebellar Ataxia Type 2

Background. Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease presenting with redox imbalance. However, the nature and implications of redox imbalance in SCA2 physiopathology have not been fully understood. Objective. The objective of this study is to assess the redox imbalance and its association with disease severity in SCA2 mutation carriers. Methods. A case-control study was conducted involving molecularly confirmed SCA2 patients, presymptomatic individuals, and healthy controls. Several antioxidant parameters were assessed, including serum thiol concentration and the superoxide dismutase, catalase, and glutathione S-transferase enzymatic activities. Also, several prooxidant parameters were evaluated, including thiobarbituric acid-reactive species and protein carbonyl concentrations. Damage, protective, and OXY scores were computed. Clinical correlates were established. Results. Significant differences were found between comparison groups for redox markers, including protein carbonyl concentration (F=3.30; p=0.041), glutathione S-transferase activity (F=4.88; p=0.009), and damage (F=3.20; p=0.045), protection (F=12.75; p<0.001), and OXY (F=7.29; p=0.001) scores. Protein carbonyl concentration was positively correlated with CAG repeat length (r=0.27; p=0.022), while both protein carbonyl concentration (r=−0.27; p=0.018) and OXY score (r=−0.25; p=0.013) were inversely correlated to the disease duration. Increasing levels of antioxidants and decreasing levels of prooxidant parameters were associated with clinical worsening. Conclusions. There is a disruption of redox balance in SCA2 mutation carriers which depends on the disease stage. Besides, redox changes associate with markers of disease severity, suggesting a link between disruption of redox balance and SCA2 physiopathology

<i>De Novo</i> Mutations in Ataxin-2 Gene and ALS Risk

<div><p>Pathogenic CAG repeat expansion in the ataxin-2 gene (<i>ATXN2</i>) 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 <i>de novo</i> mutations in <i>ATXN2</i> with autosomal dominant ALS. These findings support our previous conjectures based on population studies on the role of large normal <i>ATXN2</i> alleles as the source for new mutations being involved in neurodegenerative pathologies associated with CAG expansions. The <i>de novo</i> 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 <i>ATXN2</i>. Higher risk for ALS was associated with pathogenic CAG repeat as revealed by meta-analysis.</p></div

Genetic markers for <i>ATXN2</i> haplotyping and gene sequencing.

<p>A) <i>ATXN2</i> gene schematic maps and microsatellite, D12S1333 (telomeric at 200 kb from <i>ATXN2</i>), D12S1672 (intragenic at exon 1) and D12S1332 (centromeric at 350 kb from <i>ATXN2</i>) and SNIPs markers, rs695871 (at 177 bp upstream CAG expansion), rs695872 (at 106 bp upstream CAG expansion) and rs390624 (within the expanded CAG) used for haplotyping cases involved in <i>de novo</i> mutations, the polymorphic (CCG)nCCC/poly-proline adjacent to the CAG expansion is also indicated. B) Sequencing for case II-10, mother of the proband III-16 (25 CAG with only one CAA interruption). C) Relative position for other SNPs situated either within or near the expanded CAG.</p

Meta-analyses for large and intermediate CAG lengths in <i>ATXN2</i>.

<p>Galbraith (A–C) and forest plots (D–F) for different <i>ATXN2</i> CAG length across populations. A) and D) ≥24/27 CAG. B) and E) ≥30 CAG. C) and F) ≥32 CAG.</p

Table. 2. Microsatellite haplotypes.

<p>NA: Not available, Inferred haplotype are bracketed,</p>*<p>sick by history.</p

Phenotype and <i>ATXN2</i> genotype for ALS case series.

<p>Affected by history and genotype inferred from daugther.</p>*<p>De novo mutation causing disease. <b>EERC</b>: El Escorial Revised Classification.</p

Genetics, EMG and MRI analysis.

<p>A) Electrophoresis of fluorescent fragment analysis of <i>ATXN2</i> CAG repeat. In each lane, the content is specified. B) Fasciculation patterns in proband’s tongue and in biceps brachii recorded by EMG. C) Midsagittal MRI image of proband, no cerebellar atrophy is evident. D) Representative 3% agarose electrophoresis of <i>C9ORF72</i> analysis in index case and parents (lanes 2, 3, 4). Lanes 1and 8: MW markers (Ready Load™ 1–12.216 Kb ladder and 250–3500 bp ladder in multiples of 250 bp (Invitrogen), respectively; Lane 7: mock; lanes 2, 3, 4: case III-16, and both parents II-9 and II-10, respectively. Note that each DNA showed two defined bands despite PCR products with 7-deaza-2-deoxy GTP stain poorly with ethidium bromide. These 3 samples were heterozygous with bands higher than 250 bp but bellow 350 bp (hex repeat ∼11units) using Renton et al. primers anchoring 280 bp from hex-repeat. Lanes 5, 6 are unrelated ALS cases from the Cuban population.</p

General mechanisms for <i>ATXN2</i> gene <i>de novo</i> mutagenesis in the population.

<p>Two models can be proposed for explanation of <i>de novo</i> CAG expansions in <i>ATXN2</i>. Both involve loss of the CAA interruption in large alleles resulting in a minimal length of pure repeat within the CAG expansion. CAA interruptions break the CAG tract in discrete repeat arrays protecting it from instability <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0070560#pone.0070560-Ross1" target="_blank">[17]</a>. According to this study, the minimal length of the internal pure repeat leading to <i>de novo</i> mutations is 8 CAG.</p