De novo GRIN variants in M3 helix associated with neurological disorders control channel gating of NMDA receptor.

N-methyl-D-aspartate receptors (NMDARs) are members of the glutamate receptor family and participate in excitatory postsynaptic transmission throughout the central nervous system. Genetic variants in GRIN genes encoding NMDAR subunits are associated with a spectrum of neurological disorders. The M3 transmembrane helices of the NMDAR couple directly to the agonist-binding domains and form a helical bundle crossing in the closed receptors that occludes the pore. The M3 functions as a transduction element whose conformational change couples ligand binding to opening of an ion conducting pore. In this study, we report the functional consequences of 48 de novo missense variants in GRIN1, GRIN2A, and GRIN2B that alter residues in the M3 transmembrane helix. These de novo variants were identified in children with neurological and neuropsychiatric disorders including epilepsy, developmental delay, intellectual disability, hypotonia and attention deficit hyperactivity disorder. All 48 variants in M3 for which comprehensive testing was completed produce a gain-of-function (28/48) compared to loss-of-function (9/48); 11 variants had an indeterminant phenotype. This supports the idea that a key structural feature of the M3 gate exists to stabilize the closed state so that agonist binding can drive channel opening. Given that most M3 variants enhance channel gating, we assessed the potency of FDA-approved NMDAR channel blockers on these variant receptors. These data provide new insight into the structure-function relationship of the NMDAR gate, and suggest that variants within the M3 transmembrane helix produce a gain-of-function.

Cardiopulmonary exercise testing on adaptive equipment in children and adults with Friedreich ataxia.

INTRODUCTION/AIMS: Traditional exercise is often difficult for individuals with Friedreich ataxia (FRDA), and evidence is limited regarding how to measure exercise performance in this population. We evaluated the feasibility, reliability, and natural history of adaptive cardiopulmonary exercise test (CPET) performance in children and adults with FRDA. METHODS: Participants underwent CPET on either an arm cycle ergometer (ACE) or recumbent leg cycle ergometer (RLCE) at up to four visits (baseline, 2 weeks, 4 weeks, and 1 year). Maximum work, oxygen consumption (peak VO2), oxygen (O2) pulse, and anaerobic threshold (AT) were measured in those who reached maximal volition. Test-retest reliability was assessed with intraclass coefficients, and longitudinal change was assessed using regression analysis. RESULTS: In our cohort (N = 23), median age was 18 years (interquartile range [IQR], 14-23), median age of FRDA onset was 8 years (IQR 6-13), median Friedreich Ataxia Rating Scale score was 58 (IQR 54-62), and GAA repeat length on the shorter FXN allele (GAA1) was 766 (IQR, 650-900). Twenty-one (91%) completed a maximal CPET (n = 8, ACE and n = 13, RLCE). Age, sex, and GAA1 repeat length were each associated with peak VO2. Preliminary estimates demonstrated reasonable agreement between visits 2 and 3 for peak work by both ACE and RLCE, and for peak VO2, O2 pulse, and AT by RLCE. We did not detect significant performance changes over 1 year. DISCUSSION: Adaptive CPET is feasible in FRDA, a relevant clinical trial outcome for interventions that impact exercise performance and will increase access to participation as well as generalizability of findings.

FXN gene methylation determines carrier status in Friedreich ataxia.

BACKGROUND: Friedreich ataxia (FRDA) is typically caused by homozygosity for an expanded GAA triplet-repeat (GAA-TRE) in intron 1 of the FXN gene. Some patients are compound heterozygous for the GAA-TRE and another FXN pathogenic variant. Detection of the GAA-TRE in the heterozygous state, occasionally technically challenging, is essential for diagnosing compound heterozygotes and asymptomatic carriers. OBJECTIVE: We explored if the FRDA differentially methylated region (FRDA-DMR) in intron 1, which is hypermethylated in cis with the GAA-TRE, effectively detects heterozygous GAA-TRE. METHODS: FXN DNA methylation was assayed by targeted bisulfite deep sequencing using the Illumina platform. RESULTS: FRDA-DMR methylation effectively identified a cohort of known heterozygous carriers of the GAA-TRE. In an individual with clinical features of FRDA, commercial testing showed a paternally inherited pathogenic FXN initiation codon variant but no GAA-TRE. Methylation in the FRDA-DMR effectively identified the proband, his mother and various maternal relatives as heterozygous carriers of the GAA-TRE, thus confirming the diagnosis of FRDA. CONCLUSION: FXN DNA methylation reliably detects the GAA-TRE in the heterozygous state and offers a robust alternative strategy to diagnose FRDA due to compound heterozygosity and to identify asymptomatic heterozygous carriers of the GAA-TRE.

Characterization of Cardiac-Onset Initial Presentation in Friedreich Ataxia.

We examined the clinical features of Friedreich ataxia (FRDA) patients who present first with cardiac disease in order to understand the earliest features of the diagnostic journey in FRDA. We identified a group of subjects in the FACOMS natural history study whose first identified clinical feature was cardiac. Only 0.5% of the total cohort belonged to this group, which was younger on average at the time of presentation. Their cardiac symptoms ranged from asymptomatic features to heart failure with severe systolic dysfunction. Two of those individuals with severe dysfunction proceeded to heart transplantation, but others spontaneously recovered. In most cases, diagnosis of FRDA was not made until well after cardiac presentation. The present study shows that some FRDA patients present based on cardiac features, suggesting that earlier identification of FRDA might occur through enhancing awareness of FRDA among pediatric cardiologists who see such patients. This is important in the context of newly identified therapies for FRDA.

Methylated and unmethylated epialleles support variegated epigenetic silencing in Friedreich ataxia.

Friedreich ataxia (FRDA) is typically caused by homozygosity for an expanded GAA triplet-repeat in intron 1 of the FXN gene, which results in transcriptional deficiency via epigenetic silencing. Most patients are homozygous for alleles containing > 500 triplets, but a subset (~20%) have at least one expanded allele with < 500 triplets and a distinctly milder phenotype. We show that in FRDA DNA methylation spreads upstream from the expanded repeat, further than previously recognized, and establishes an FRDA-specific region of hypermethylation in intron 1 (~90% in FRDA versus < 10% in non-FRDA) as a novel epigenetic signature. The hypermethylation of this differentially methylated region (FRDA-DMR) was observed in a variety of patient-derived cells; it significantly correlated with FXN transcriptional deficiency and age of onset, and it reverted to the non-disease state in isogenically corrected induced pluripotent stem cell (iPSC)-derived neurons. Bisulfite deep sequencing of the FRDA-DMR in peripheral blood mononuclear cells from 73 FRDA patients revealed considerable intra-individual epiallelic variability, including fully methylated, partially methylated, and unmethylated epialleles. Although unmethylated epialleles were rare (median = 0.33%) in typical patients homozygous for long GAA alleles with > 500 triplets, a significantly higher prevalence of unmethylated epialleles (median = 9.8%) was observed in patients with at least one allele containing < 500 triplets, less severe FXN deficiency (>20%) and later onset (>15 years). The higher prevalence in mild FRDA of somatic FXN epialleles devoid of DNA methylation is consistent with variegated epigenetic silencing mediated by expanded triplet-repeats. The proportion of unsilenced somatic FXN genes is an unrecognized phenotypic determinant in FRDA and has implications for the deployment of effective therapies.

Liquid Chromatography-Mass Spectrometry Analysis of Frataxin Proteoforms in Whole Blood as Biomarkers of the Genetic Disease Friedreich's Ataxia.

Friedreich's ataxia (FRDA) is caused primarily by expanded GAA repeats in intron 1 of both alleles of the FXN gene, which causes transcriptional silencing and reduced expression of frataxin mRNA and protein. FRDA is characterized by slowly progressive ataxia and cardiomyopathy. Symptoms generally appear during adolescence, and patients slowly progress to wheelchair dependency usually in the late teens or early twenties with death on average in the 4th decade. There are two known mature proteoforms of frataxin. Mitochondrial frataxin (frataxin-M) is a 130-amino acid protein with a molecular weight of 14,268 Da, and there is an alternatively spliced N-terminally acetylated 135-amino acid form (frataxin-E) with a molecular weight of 14,953 Da found in erythrocytes. There is reduced expression of frataxin in the heart and brain, but frataxin is not secreted into the systemic circulation, so it cannot be analyzed in serum or plasma. Blood is a readily accessible biofluid that contains numerous different cell types that express frataxin. We have found that pig blood can serve as an excellent surrogate matrix to validate an assay for frataxin proteoforms because pig frataxin is lost during the immunoprecipitation step used to isolate human frataxin. Frataxin-M is expressed in blood cells that contain mitochondria, whereas extra-mitochondrial frataxin-E is found in erythrocytes. This means that the analysis of frataxin in whole blood provides information on the concentration of both proteoforms without having to isolate the individual cell types. In the current study, we observed that the distributions of frataxin levels for a sample of 25 healthy controls and 50 FRDA patients were completely separated from each other, suggesting 100% specificity and 100% sensitivity for distinguishing healthy controls from FRDA cases, a very unusual finding for a biomarker assay. Additionally, frataxin levels were significantly correlated with the GAA repeat length and age of onset with higher correlations for extra-mitochondrial frataxin-E than those for mitochondrial frataxin-M. These findings auger well for using frataxin levels measured by the validated stable isotope dilution ultrahigh-performance liquid chromatography-multiple reaction monitoring/mass spectrometry assay to monitor therapeutic interventions and the natural history of FRDA. Our study also illustrates the utility of using whole blood for protein disease biomarker discovery and validation.

A Novel Metric for Predicting Severity of Disease Features in Friedreich's Ataxia.

BACKGROUND: Friedreich's ataxia (FRDA), most commonly caused by a GAA triplet repeat (GAA-TR) expansion in intron 1 of the FXN gene, is characterized by deficiency of frataxin protein and clinical features such as progressive ataxia, dysarthria, impaired proprioception and vibration, abolished deep tendon reflexes, Babinski sign, and vision loss in association with non-neurological features such as skeletal anomalies, hearing loss, cardiomyopathy, and diabetes. Pathogenic GAA-TRs range in size from 60 to 1500 triplets and negatively correlate with age of onset. Clinical severity is predicted by a combination of GAA-TR length and disease duration (DD) via multivariable regressions, which cannot typically be used for the small sample sizes in most studies on this rare disease. OBJECTIVE: We aimed to develop a single metric, which we call "disease burden" (DB), that encompasses both GAA-TR length and DD for predicting disease features of FRDA in small sample sizes. METHODS: Linear regression and multivariable regression analysis was used to determine correlation coefficients between different disease features of FRDA. RESULTS: Using large datasets for validation, we found that DB predicts measures of neurological dysfunction in FRDA better than GAA-TR length or DD. Analogous results were found using small datasets. CONCLUSIONS: FRDA DB is a novel metric of disease severity that has utility in small datasets to demonstrate correlations that would not otherwise be evident with either GAA-TR or DD alone. This is important for discovering new biomarkers, as well as improving the prediction of severity of disease features in FRDA. © 2023 International Parkinson and Movement Disorder Society.

Efficacy of Omaveloxolone in Friedreich's Ataxia: Delayed-Start Analysis of the MOXIe Extension.

BACKGROUND: MOXIe was a two-part study evaluating the safety and efficacy of omaveloxolone in patients with Friedreich's ataxia, a rare, progressive neurological disease with no proven therapy. MOXIe part 2, a randomized double-blind placebo-controlled trial, showed omaveloxolone significantly improved modified Friedreich's Ataxia Rating Scale (mFARS) scores relative to placebo. Patients who completed part 1 or 2 were eligible to receive omaveloxolone in an open-label extension study. OBJECTIVE: The delayed-start study compared mFARS scores at the end of MOXIe part 2 with those at 72 weeks in the open-label extension period (up to 144 weeks) for patients initially randomized to omaveloxolone versus those initially randomized to placebo. METHODS: We performed a noninferiority test to compare the difference between treatment groups (placebo to omaveloxolone versus omaveloxolone to omaveloxolone) using a single mixed model repeated measures (MMRM) model. In addition, slopes of the change in mFARS scores were compared between both groups in the open-label extension. RESULTS: The noninferiority testing demonstrated that the difference in mFARS between omaveloxolone and placebo observed at the end of placebo-controlled MOXIe part 2 (-2.17 ± 1.09 points) was preserved after 72 weeks in the extension (-2.91 ± 1.44 points). In addition, patients previously randomized to omaveloxolone in MOXIe part 2 continued to show no worsening in mFARS relative to their extension baseline through 144 weeks. CONCLUSIONS: These results support the positive results of MOXIe part 2 and indicate a persistent benefit of omaveloxolone treatment on disease course in Friedreich's ataxia. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Reverse Phase Protein Array Reveals Correlation of Retinoic Acid Metabolism With Cardiomyopathy in Friedreich's Ataxia.

Identifying biomarkers is important for assessment of disease progression, prediction of symptom development, and determination of treatment effectiveness. While unbiased analyses of differential gene expression using next-generation sequencing methods are now routinely conducted, proteomics studies are more challenging because of traditional methods predominantly being low throughput and offering a limited dynamic range for simultaneous detection of hundreds of proteins that drastically differ in their intracellular abundance. We utilized a sensitive and high-throughput proteomic technique, reverse phase protein array (RPPA), to attain protein expression profiles of primary fibroblasts obtained from patients with Friedreich's ataxia (FRDA) and unaffected controls (CTRLs). The RPPA was designed to detect 217 proteins or phosphorylated proteins by individual antibody, and the specificity of each antibody was validated prior to the experiment. Among 62 fibroblast samples (44 FRDA and 18 CTRLs) analyzed, 30 proteins/phosphoproteins were significantly changed in FRDA fibroblasts compared with CTRL cells (p < 0.05), mostly representing signaling molecules and metabolic enzymes. As expected, frataxin was significantly downregulated in FRDA samples, thus serving as an internal CTRL for assay integrity. Extensive bioinformatics analyses were conducted to correlate differentially expressed proteins with critical disease parameters (e.g., selected symptoms, age of onset, guanine-adenine-adenine sizes, frataxin levels, and Functional Assessment Rating Scale scores). Members of the integrin family of proteins specifically associated with hearing loss in FRDA. Also, RPPA data, combined with results of transcriptome profiling, uncovered defects in the retinoic acid metabolism pathway in FRDA samples. Moreover, expression of aldehyde dehydrogenase family 1 member A3 differed significantly between cardiomyopathy-positive and cardiomyopathy-negative FRDA cohorts, demonstrating that metabolites such as retinol, retinal, or retinoic acid could become potential predictive biomarkers of cardiac presentation in FRDA.

Targeting 3' and 5' untranslated regions with antisense oligonucleotides to stabilize frataxin mRNA and increase protein expression.

Friedreich's ataxia (FRDA) is a severe multisystem disease caused by transcriptional repression induced by expanded GAA repeats located in intron 1 of the Frataxin (FXN) gene encoding frataxin. FRDA results from decreased levels of frataxin; thus, stabilization of the FXN mRNA already present in patient cells represents an attractive and unexplored therapeutic avenue. In this work, we pursued a novel approach based on oligonucleotide-mediated targeting of FXN mRNA ends to extend its half-life and availability as a template for translation. We demonstrated that oligonucleotides designed to bind to FXN 5' or 3' noncoding regions can increase FXN mRNA and protein levels. Simultaneous delivery of oligonucleotides targeting both ends increases efficacy of the treatment. The approach was confirmed in several FRDA fibroblast and induced pluripotent stem cell-derived neuronal progenitor lines. RNA sequencing and single-cell expression analyses confirmed oligonucleotide-mediated FXN mRNA upregulation. Mechanistically, a significant elongation of the FXN mRNA half-life without any changes in chromatin status at the FXN gene was observed upon treatment with end-targeting oligonucleotides, indicating that transcript stabilization is responsible for frataxin upregulation. These results identify a novel approach toward upregulation of steady-state mRNA levels via oligonucleotide-mediated end targeting that may be of significance to any condition resulting from transcription downregulation.

Skin fibroblast metabolomic profiling reveals that lipid dysfunction predicts the severity of Friedreich's ataxia.

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a triplet guanine-adenine-adenine (GAA) repeat expansion in intron 1 of the FXN gene, which leads to decreased levels of the frataxin protein. Frataxin is involved in the formation of iron-sulfur (Fe-S) cluster prosthetic groups for various metabolic enzymes. To provide a better understanding of the metabolic status of patients with FRDA, here we used patient-derived fibroblast cells as a surrogate tissue for metabolic and lipidomic profiling by liquid chromatography-high resolution mass spectrometry. We found elevated HMG-CoA and ß-hydroxybutyrate-CoA levels, implying dysregulated fatty acid oxidation, which was further demonstrated by elevated acyl-carnitine levels. Lipidomic profiling identified dysregulated levels of several lipid classes in FRDA fibroblast cells when compared with non-FRDA fibroblast cells. For example, levels of several ceramides were significantly increased in FRDA fibroblast cells; these results positively correlated with the GAA repeat length and negatively correlated with the frataxin protein levels. Furthermore, stable isotope tracing experiments indicated increased ceramide synthesis, especially for long-chain fatty acid-ceramides, in FRDA fibroblast cells compared with ceramide synthesis in healthy control fibroblast cells. In addition, PUFA-containing triglycerides and phosphatidylglycerols were enriched in FRDA fibroblast cells and negatively correlated with frataxin levels, suggesting lipid remodeling as a result of FXN deficiency. Altogether, we demonstrate patient-derived fibroblast cells exhibited dysregulated metabolic capabilities, and their lipid dysfunction predicted the severity of FRDA, making them a useful surrogate to study the metabolic status in FRDA.

Safety and Efficacy of Omaveloxolone in Friedreich Ataxia (MOXIe Study).

OBJECTIVE: Friedreich ataxia (FA) is a progressive genetic neurodegenerative disorder with no approved treatment. Omaveloxolone, an Nrf2 activator, improves mitochondrial function, restores redox balance, and reduces inflammation in models of FA. We investigated the safety and efficacy of omaveloxolone in patients with FA. METHODS: We conducted an international, double-blind, randomized, placebo-controlled, parallel-group, registrational phase 2 trial at 11 institutions in the United States, Europe, and Australia (NCT02255435, EudraCT2015-002762-23). Eligible patients, 16 to 40 years of age with genetically confirmed FA and baseline modified Friedreich's Ataxia Rating Scale (mFARS) scores between 20 and 80, were randomized 1:1 to placebo or 150mg per day of omaveloxolone. The primary outcome was change from baseline in the mFARS score in those treated with omaveloxolone compared with those on placebo at 48 weeks. RESULTS: One hundred fifty-five patients were screened, and 103 were randomly assigned to receive omaveloxolone (n = 51) or placebo (n = 52), with 40 omaveloxolone patients and 42 placebo patients analyzed in the full analysis set. Changes from baseline in mFARS scores in omaveloxolone (-1.55 ± 0.69) and placebo (0.85 ± 0.64) patients showed a difference between treatment groups of -2.40 ± 0.96 (p = 0.014). Transient reversible increases in aminotransferase levels were observed with omaveloxolone without increases in total bilirubin or other signs of liver injury. Headache, nausea, and fatigue were also more common among patients receiving omaveloxolone. INTERPRETATION: In the MOXIe trial, omaveloxolone significantly improved neurological function compared to placebo and was generally safe and well tolerated. It represents a potential therapeutic agent in FA. ANN NEUROL 2021;89:212-225.

PPAR gamma agonist leriglitazone improves frataxin-loss impairments in cellular and animal models of Friedreich Ataxia.

Friedreich ataxia (FRDA), the most common autosomal recessive ataxia, is characterized by degeneration of the large sensory neurons and spinocerebellar tracts, cardiomyopathy, and increased incidence in diabetes. The underlying pathophysiological mechanism of FRDA, driven by a significantly decreased expression of frataxin (FXN), involves increased oxidative stress, reduced activity of enzymes containing iron­sulfur clusters (ISC), defective energy production, calcium dyshomeostasis, and impaired mitochondrial biogenesis, leading to mitochondrial dysfunction. The peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcriptional factor playing a key role in mitochondrial function and biogenesis, fatty acid storage, energy metabolism, and antioxidant defence. It has been previously shown that the PPARγ/PPARγ coactivator 1 alpha (PGC-1α) pathway is dysregulated when there is frataxin deficiency, thus contributing to FRDA pathogenesis and supporting the PPARγ pathway as a potential therapeutic target. Here we assess whether MIN-102 (INN: leriglitazone), a novel brain penetrant and orally bioavailable PPARγ agonist with an improved profile for central nervous system (CNS) diseases, rescues phenotypic features in cellular and animal models of FRDA. In frataxin-deficient dorsal root ganglia (DRG) neurons, leriglitazone increased frataxin protein levels, reduced neurite degeneration and α-fodrin cleavage mediated by calpain and caspase 3, and increased survival. Leriglitazone also restored mitochondrial membrane potential and partially reversed decreased levels of mitochondrial Na+/Ca2+ exchanger (NCLX), resulting in an improvement of mitochondrial functions and calcium homeostasis. In frataxin-deficient primary neonatal cardiomyocytes, leriglitazone prevented lipid droplet accumulation without increases in frataxin levels. Furthermore, leriglitazone improved motor function deficit in YG8sR mice, a FRDA mouse model. In agreement with the role of PPARγ in mitochondrial biogenesis, leriglitazone significantly increased markers of mitochondrial biogenesis in FRDA patient cells. Overall, these results suggest that targeting the PPARγ pathway by leriglitazone may provide an efficacious therapy for FRDA increasing the mitochondrial function and biogenesis that could increase frataxin levels in compromised frataxin-deficient DRG neurons. Alternately, leriglitazone improved the energy metabolism by increasing the fatty acid ß-oxidation in frataxin-deficient cardiomyocytes without elevation of frataxin levels. This could be linked to a lack of significant mitochondrial biogenesis and cardiac hypertrophy. The results reinforced the different tissue requirement in FRDA and the pleiotropic effects of leriglitazone that could be a promising therapy for FRDA.

GRP75 overexpression rescues frataxin deficiency and mitochondrial phenotypes in Friedreich ataxia cellular models.

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by the deficiency of frataxin, a mitochondrial protein crucial for iron-sulfur cluster biogenesis and adenosine triphosphate (ATP) production. Currently, there is no therapy to slow down the progression of FRDA. Recent evidence indicates that posttranslational regulation of residual frataxin levels can rescue some of the functional deficit of FRDA, raising the possibility of enhancing levels of residual frataxin as a treatment for FRDA. Here, we present evidence that mitochondrial molecular chaperone GRP75, also known as mortalin/mthsp70/PBP74, directly interacts with frataxin both in vivo in mouse cortex and in vitro in cortical neurons. Overexpressing GRP75 increases the levels of both wild-type frataxin and clinically relevant missense frataxin variants in human embryonic kidney 293 cells, while clinical GRP75 variants such as R126W, A476T and P509S impair the binding of GRP75 with frataxin and the effect of GRP75 on frataxin levels. In addition, GRP75 overexpression rescues frataxin deficiency and abnormal cellular phenotypes such as the abnormal mitochondrial network and decreased ATP levels in FRDA patient-derived cells. The effect of GRP75 on frataxin might be in part mediated by the physical interaction between GRP75 and mitochondrial processing peptidase (MPP), which makes frataxin more accessible to MPP. As GRP75 levels are decreased in multiple cell types of FRDA patients, restoring GRP75 might be effective in treating both typical FRDA patients with two guanine-adenine-adenine repeat expansions and compound heterozygous patients with point mutations.

Mitochondrial dysfunction in the development and progression of neurodegenerative diseases.

In addition to ATP synthesis, mitochondria are highly dynamic organelles that modulate apoptosis, ferroptosis, and inflammasome activation. Through executing these varied functions, the mitochondria play critical roles in the development and progression of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Friedreich ataxia, among others. Impaired mitochondrial biogenesis and abnormal mitochondrial dynamics contribute to mitochondrial dysfunction in these diseases. Additionally, dysfunctional mitochondria play critical roles in signaling for both inflammasome activation and ferroptosis. Therapeutics are being developed to circumvent inflammasome activation and ferroptosis in dysfunctional mitochondria. Targeting these aspects of mitochondrial dysfunction may present viable therapeutic strategies for combatting the neurodegenerative diseases. This review aims to summarize the role of the mitochondria in the development and progression of neurodegenerative diseases and to present current therapeutic approaches that target mitochondrial dysfunction in these diseases.

Designing phase II clinical trials in Friedreich ataxia.

INTRODUCTION: Friedreich ataxia (FRDA) is an autosomal recessive disorder caused by deficiency of frataxin, an essential mitochondrial protein involved in iron sulfur cluster biogenesis, oxidative phosphorylation and other processes. FRDA most notably affects the heart, sensory neurons, spinal cord, cerebellum, and other brain regions, and manifests clinically as ataxia, sensory loss, dysarthria, spasticity, and hypertrophic cardiomyopathy. Therapeutic approaches in FRDA have consisted of two different approaches: (1) augmenting or restoring frataxin production and (2) modulating a variety of downstream processes related to mitochondrial dysfunction, including reactive oxygen species production, ferroptosis, or Nrf2 activation. AREAS COVERED: In this review, we summarize data from major phase II clinical trials in FRDA published between 2015 and 2020, which includes A0001/EPI743, Omaveloxolone, RT001, and Actimmune. EXPERT OPINION: A growing number of drug candidates are being tested in phase II clinical trials for FRDA; however, most have not met their primary endpoints, and none have received FDA approval. In this review, we aim to summarize completed phase II clinical trials in FRDA, outlining critical lessons that have been learned and that should be incorporated into future trial design to ultimately optimize drug development in FRDA.

Peripheral blood gene expression reveals an inflammatory transcriptomic signature in Friedreich's ataxia patients.

Transcriptional changes in Friedreich's ataxia (FRDA), a rare and debilitating recessive Mendelian neurodegenerative disorder, have been studied in affected but inaccessible tissues-such as dorsal root ganglia, sensory neurons and cerebellum-in animal models or small patient series. However, transcriptional changes induced by FRDA in peripheral blood, a readily accessible tissue, have not been characterized in a large sample. We used differential expression, association with disability stage, network analysis and enrichment analysis to characterize the peripheral blood transcriptome and identify genes that were differentially expressed in FRDA patients (n = 418) compared with both heterozygous expansion carriers (n = 228) and controls (n = 93 739 individuals in total), or were associated with disease progression, resulting in a disease signature for FRDA. We identified a transcriptional signature strongly enriched for an inflammatory innate immune response. Future studies should seek to further characterize the role of peripheral inflammation in FRDA pathology and determine its relevance to overall disease progression.

Correlation of Visual Quality of Life With Clinical and Visual Status in Friedreich Ataxia.

BACKGROUND: The primary objective was to determine the association of patient-reported vision-specific quality of life to disease status and visual function in patients with Friedreich's ataxia (FRDA). METHODS: Patients with FRDA were assessed with the 25-Item National Eye Institute Visual Functioning Questionnaire (NEI-VFQ-25) along with measures of disease status (ataxia stage) and visual function (low- and high-contrast letter acuity scores). The relations of NEI-VFQ-25 scores to those for disease status and visual function were examined. RESULTS: Scores for the NEI-VFQ-25 were lower in patients with FRDA (n = 99) compared with published disease-free controls, particularly reduced in a subgroup of FRDA patients with features of early onset, older age, and abnormal visual function. CONCLUSIONS: The NEI-VFQ-25 captures the subjective component of visual function in patients with FRDA.

Open-label pilot study of oral methylprednisolone for the treatment of patients with friedreich ataxia.

INTRODUCTION: In this study we assessed the effect of methylprednisolone on safety, tolerability, and ability in Friedreich ataxia (FRDA). METHODS: The study was an open-label trial of pulse methylprednisolone on 11 participants with FRDA. All participants followed a 28-day treatment cycle, repeated 7 times. Patients were assessed with the timed 25-foot walk (T25FW), 1-minute walk (1MW), the Friedreich Ataxia Rating Scale (FARS), and the 9-hole peg test (9HPT). Efficacy was tested by comparing baseline and week 26 visits, separated into adult and pediatric groups. RESULTS: In comparisons of participants' baseline and week 26 visits, only the pediatric cohort's 1MW score showed change (P < 0.05). The T25FW, the primary outcome measure, did not change significantly. DISCUSSION: Pediatric participants improved their gait distance in the 1MW, but did not significantly improve in other measures in this overall negative study. Methylprednisolone was generally well tolerated, suggesting that it may be useful for ambulatory children with FRDA if benefit is found with further study.

Liquid Chromatography-High Resolution Mass Spectrometry Analysis of Platelet Frataxin as a Protein Biomarker for the Rare Disease Friedreich's Ataxia.

Friedreich's ataxia (FA) is an autosomal recessive disease caused by an intronic GAA triplet expansion in the FXN gene, leading to reduced expression of the mitochondrial protein frataxin. FA is estimated to affect 1 in 50 000 with a mean age of death in the fourth decade of life. There are no approved treatments for FA, although experimental approaches, which involve up-regulation or replacement of frataxin protein, are being tested. Frataxin is undetectable in serum or plasma, and whole blood cannot be used because it is present in long-lived erythrocytes. Therefore, an assay was developed for analyzing frataxin in platelets, which have a half-life of 10 days. The assay is based on stable isotope dilution immunopurification two-dimensional nano-ultra high performance liquid chromatography/parallel reaction monitoring/mass spectrometry. The lower limit of quantification was 0.078 pg frataxin/µg protein, and the assay had 100% sensitivity and specificity for discriminating between controls and FA cases. The mean levels of control and FA platelet frataxin were 9.4 ± 2.6 and 2.4 ± 0.6 pg/µg protein, respectively. The assay should make it possible to rigorously monitor the effects of therapeutic interventions on frataxin expression in this devastating disease.