Oxidative Stress in Spinocerebellar Ataxia Type 7 Is Associated with Disease Severity.

Spinocerebellar ataxia type 7 is a neurodegenerative inherited disease caused by a CAG expansion in the coding region of the ATXN7 gene, which results in the synthesis of polyglutamine-containing ataxin-7. Expression of mutant ataxin-7 disturbs different cell processes, including transcriptional regulation, protein conformation and clearance, autophagy, and glutamate transport; however, mechanisms underlying neurodegeneration in SCA7 are still unknown. Implication of oxidative stress in the pathogenesis of various neurodegenerative diseases, including polyglutamine disorders, has recently emerged. We perform a cross-sectional study to determine for the first time pheripheral levels of different oxidative stress markers in 29 SCA7 patients and 28 age- and sex-matched healthy subjects. Patients with SCA7 exhibit oxidative damage to lipids (high levels of lipid hydroperoxides and malondialdehyde) and proteins (elevated levels of advanced oxidation protein products and protein carbonyls). Furthermore, SCA7 patients showed enhanced activity of various anti-oxidant enzymes (glutathione reductase, glutathione peroxidase, and paraoxonase) as well as increased total anti-oxidant capacity, which suggest that activation of the antioxidant defense system might occur to counteract oxidant damage. Strikingly, we found positive correlation between some altered oxidative stress markers and disease severity, as determined by different clinical scales, with early-onset patients showing a more severe disturbance of the redox system than adult-onset patients. In summay, our results suggest that oxidative stress might contribute to SCA7 pathogenesis. Furthermore, oxidative stress biomarkers that were found relevant to SCA7 in this study could be useful to follow disease progression and monitor therapeutic intervention.

A comprehensive clinical and genetic study of a large Mexican population with spinocerebellar ataxia type 7.

Spinocerebellar ataxia type 7 (SCA7) is an inherited neurodegenerative disorder characterized by progressive cerebellar ataxia associated with macular degeneration. We recently described one of the largest series of patients with SCA7 that originated from a founder effect in a Mexican population, which allowed us to perform herein the first comprehensive clinical, neurophysiological, and genetic characterization of Mexican patients with SCA7. In this study, 50 patients, categorized into adult or early phenotype, were clinically assessed using standard neurological exams and genotyped using fluorescent PCR and capillary electrophoresis. Patients with SCA7 exhibited the classical phenotype of the disease characterized by cerebellar ataxia and visual loss; however, we reported, for the first time, frontal-executive disorders and altered sensory-motor peripheral neuropathy in these patients. Semiquantitative analysis of ataxia-associated symptoms was performed using Scale for the Assessment and Rating of Ataxia (SARA) and the Brief Ataxia Rating Scale (BARS) scores, while extracerebellar features were measured employing the Inventory of Non-ataxia Symptoms (INAS) scale. Ataxia rating scales confirmed the critical role size of cytosine-adenine-guanine (CAG) repeat size on age at onset and disease severity, while analysis of CAG repeat instability showed that paternal rather than maternal transmission led to greater instability.

Analysis of CAG repeats in five SCA loci in Mexican population: epidemiological evidence of a SCA7 founder effect.

Spinocerebellar ataxias (SCA) are a heterogeneous group of neurodegenerative disorders. CAG (cytosine-adenine-guanine) trinucleotide repeat expansions in the causative genes have been identified as the cause of different SCA. In this study, we simultaneously genotyped SCA1, SCA2, SCA3, SCA6, and SCA7 applying a fluorescent multiplex polymerase chain reaction assay. We analyzed 10 families with SCA (64 patients) from five different communities of Veracruz, a Mexican southeastern state, and identified 55 patients for SCA7 and 9 for SCA2, but none for SCA1, SCA3, or SCA6. To our knowledge, this sample represents one of the largest series of SCA7 cases reported worldwide. Genotyping of 300 healthy individuals from Mexican population and compiled data from different ethnicities showed discordant results concerning the hypothesis that SCA disease alleles arise by expansion of large normal alleles.

Origin of the spinocerebellar ataxia type 7 gene mutation in Mexican population.

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder characterized by progressive cerebellar ataxia associated with macular degeneration that leads, in the majority of patients, to loss of autonomy and blindness. The cause of the disease has been identified as (CAG) n repeat expansion in the coding sequence of the ATXN7 gene on chromosome 3p21.1. SCA7 is one of the least common genetically verified autosomal dominant cerebellar ataxias found worldwide; however, we previously identified the Mexican population showing high prevalence of SCA7, suggesting the occurrence of a common founder effect. In this study, haplotype analysis using four SCA7 gene-linked markers revealed that all 72 SCA7 carriers studied share a common haplotype, A-254-82-98, for the intragenic marker 3145G/A and centromeric markers D3S1287, D3S1228, and D3S3635, respectively. This multiloci combination is uncommon in healthy relatives and Mexican general population, suggesting that a single ancestral mutation is responsible for all SCA7 cases in this population. Furthermore, genotyping using 17 short tandem repeat markers from the non-recombining region of the Y chromosome and further phylogenetic relationship analysis revealed that Mexican patients possess the Western European ancestry, which might trace the SCA7 ancestral mutation to that world region.

Distribution of CTG repeats at the DMPK gene in myotonic dystrophy patients and healthy individuals from the Mexican population.

Myotonic dystrophy type 1 (DM1), the most common form of adult muscular dystrophy, is caused by anormal expansion of CTG trinucleotide repeats located in the 3'-untranslated region of the DMPK gene. The clinical features of DM1 are multisystemic and highly variable, and the unstable nature of CTG expansion causes wide genotypic and phenotypic presentations. In this study, we described to our knowledge for the first time the molecular diagnosis of myotonic dystrophy type 1 patients in the Mexican population, applying a fluorescent PCR method in combination with capillary electrophoresis analysis of the amplified products. We identified expanded alleles in 45 out of 50 patients (90%) with clinical features of myotonic disease. Furthermore, genotyping of 400 healthy subjects revealed the presence of 25 different alleles, ranging in size from 5 to 34 repeats. The most frequent allele was 13 CTG repeats (38.87%) and the frequency for alleles over 18 CTG repeats was 6.7%. Molecular test is essential for DM1 diagnosis and distribution of the CTG repeat alleles present in the Mexican population are significantly different from those of other populations.