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Scientific News

FARA funds research progress

In this section, you will find the most recent FA research publications, many of which are funded by FARA, as well as information on upcoming conferences and symposiums. You can search for articles by date using the archive box in the right hand column. To locate FARA Funded or Supported Research, click the hyperlink in the right hand column. You may also search for specific content using key words or phrases in the search button at the top right of your screen. Please be sure to visit other key research sections of our website for information on FARA’s Grant Program and the Treatment Pipeline.

R-loops promote trinucleotide repeat deletion through DNA base excision repair enzymatic activities

Trinucleotide repeat (TNR) expansion and deletion are responsible for over 40 neurodegenerative diseases and associated with cancer. TNR can undergo somatic instability that is mediated by DNA damage and repair, and gene transcription. Recent studies have pointed towards a role for R-loops in causing TNR expansion and deletion, and it's been shown that base excision repair (BER) can result in CAG repeat deletions from R-loops in yeast. However, it remains unknown how BER in R-loops can mediate TNR instability. In this study, using biochemical approaches, the authors examined BER enzymatic activities and their influence on TNR-R-loops. This study found that AP endonuclease 1 incised an abasic site on the non-template strand of a TNR R-loop, creating a double-flap intermediate containing an RNA-DNA hybrid that subsequently inhibited pol β DNA synthesis of TNRs. This stimulated flap endonuclease 1 (FEN1) cleavage of TNRs engaged in an R-loop. Moreover, the authors showed that FEN1 also efficiently cleaved the RNA strand, facilitating pol β loop/hairpin bypass synthesis and the resolution of TNR R-loops through BER. Consequently, this resulted in fewer TNRs synthesized by pol β than those removed by FEN1, thereby leading to repeat deletion. These results indicate that TNR R-loops preferentially lead to repeat deletion during BER by disrupting the balance between the addition and removal of TNRs. These discoveries open a new avenue for the treatments and prevention of repeat expansion diseases and cancer.

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Onset features and time to diagnosis in Friedreich's Ataxia

In rare disorders diagnosis may be delayed due to limited awareness and unspecific presenting symptoms. This study addresses the issue of diagnostic delay in Friedreich's Ataxia (FRDA). Six hundred eleven genetically confirmed FRDA patients were recruited within a multicentric natural history study conducted by the EFACTS (European FRDA Consortium for Translational Studies, -Identifier NCT02069509). Age at first symptoms as well as age at first suspicion of FRDA by a physician were collected retrospectively at the baseline visit. In 554 of cases (90.7%), disease presented with gait or coordination disturbances. In the others (n = 57, 9.3%), non-neurological features such as scoliosis or cardiomyopathy predated ataxia. Before the discovery of the causal mutation in 1996, median time to diagnosis was 4(IQR = 2-9) years and it improved significantly after the introduction of genetic testing (2(IQR = 1-5) years, p < 0.001). Still, after 1996, time to diagnosis was longer in patients with a) non-neurological presentation (mean 6.7, 95%CI [5.5,7.9] vs 4.5, [4.2,5] years in those with neurological presentation, p = 0.001) as well as in b) patients with late-onset (3(IQR = 1-7) vs 2(IQR = 1-5) years compared to typical onset < 25 years of age, p = 0.03). Age at onset significantly correlated with the length of the shorter GAA repeat (GAA1) in case of neurological onset (r = - 0,6; p < 0,0001), but not in patients with non-neurological presentation (r = - 0,1; p = 0,4). Across 54 siblings' pairs, differences in age at onset did not correlate with differences in GAA-repeat length (r = - 0,14, p = 0,3). In the genetic era, presentation with non-neurological features or in the adulthood still leads to a significant diagnostic delay in FRDA. Well-known correlations between GAA1 repeat length and disease milestones are not valid in case of atypical presentations or positive family history.

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A Drosophila model of Friedreich Ataxia with CRISPR/Cas9 insertion of GAA repeats in the frataxin gene reveals in vivo protection by N-acetyl cysteine

Thanks to the high degree of frataxin conservation, the Drosophila melanogaster fruitfly appears as an adequate animal model to study Friedreich Ataxia (FA) and to evaluate therapeutic interventions. The authors generated a Drosophila model of FA with CRISPR/Cas9 insertion of approximately 200 GAA in the intron of the fly frataxin gene fh. These flies exhibit a developmental delay and lethality associated with decreased frataxin expression. Preadult lethality was by-passed using genetic tools to overexpress frataxin only during the developmental period. These frataxin-deficient adults are short-lived and present strong locomotor defects. RNA-Seq analysis identified deregulation of genes involved in amino-acid metabolism and transcriptomic signatures of oxidative stress. In particular, this group observed a progressive increase of Tspo expression, fully rescued by adult frataxin expression. Thus, Tspo expression constitutes a molecular marker of the disease progression in this fly model and might be of interest in other animal models or in patients. Finally, in a candidate drug screening, it was observed that N-acetyl cysteine improved the survival, locomotor function, resistance to oxidative stress and aconitase activity of frataxin-deficient flies. Therefore, this model provides the opportunity to elucidate in vivo the protective mechanisms of this molecule of therapeutic potential. This study also highlights the strength of the CRISPR/Cas9 technology to introduce human mutations in endogenous orthologous genes, leading to Drosophila models of human diseases with improved physiological relevance.

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Antioxidant Defense Mechanisms and its Dysfunctional Regulation in the Mitochondrial Disease, Friedreich's Ataxia

Redox stress is associated with the pathogenesis of a wide variety of disease states. This can be amplified potentially through redox active iron deposits in oxidatively active organelles such as the mitochondrion. There are a number of disease states, including Friedreich's ataxia (FA) and sideroblastic anemia, where iron metabolism is dysregulated and leads to mitochondrial iron accumulation. Considering FA, which is due to the decreased expression of the mitochondrial protein, frataxin, this iron accumulation does not occur within protective storage proteins such as mitochondrial ferritin. Instead, it forms unbound biomineral aggregates composed of high spin iron(III), phosphorous and sulfur, which probably contributes to the observed redox stress. There is also a dysregulated response to the ensuing redox assault, as the master regulator of oxidative stress, nuclear factor erythroid 2-related factor-2 (Nrf2), demonstrates marked down-regulation. The dysfunctional response of Nrf2 in FA is due to multiple mechanisms including: (1) up-regulation of Keap1 that is involved in Nrf2 degradation; (2) activation of the nuclear Nrf2 export/degradation machinery via glycogen synthase kinase-3β (Gsk3β) signaling; and (3) inhibited nuclear translocation of Nrf2. More recently, increased microRNA (miRNA) 144 expression has been demonstrated to down-regulate Nrf2 in several disease states, including an animal model of FA. Other miRNAs have also demonstrated to be dysregulated upon frataxin depletion in vivo in humans and animal models of FA. Collectively, frataxin depletion results in multiple, complex responses that lead to detrimental redox effects that could contribute to the mechanisms involved in the pathogenesis of FA.

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Toward quantitative neuroimaging biomarkers for Friedreich's ataxia at 7 Tesla: Susceptibility mapping, diffusion imaging, R 2 and R 1 relaxometry

Ten (Friedreich's ataxia) FRDA patients (mean age 37 ± 14 years; four female) and 10 age- and sex-matched controls were included. Acquisition of magnetic resonance imaging (MRI) data for quantitative susceptibility mapping, R1 , R2 relaxometry and diffusion imaging was performed at 7 Tesla. Results of volume of interest (VOI)-based analyses of the quantitative data were compared with a voxel-based morphometry (VBM) evaluation. Differences between patients and controls were assessed using the analysis of covariance (ANCOVA; p < 0.01) with age and sex as covariates, effect size of group differences, and correlations with disease characteristics with Spearman correlation coefficient. For the VBM analysis, a statistical threshold of 0.001 for uncorrected and 0.05 for corrected p-values was used. Statistically significant differences between FRDA patients and controls were found in five out of twelve investigated structures, and statistically significant correlations with disease characteristics were revealed. Moreover, VBM revealed significant white matter atrophy within regions of the brainstem, and the cerebellum. These regions overlapped partially with brain regions for which significant differences between healthy controls and patients were found in the VOI-based quantitative MRI evaluation. It was shown that two independent analyses provided overlapping results. Moreover, positive results on correlations with disease characteristics were found, indicating that these quantitative MRI parameters could provide more detailed information and assist the search for effective treatments.

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