Friedreich's Ataxia (FRDA) is a rare neurological disorder caused by an abnormal expansion of Guanine-Adenine-Adenine (GAA) repeat in intron 1 of the FXN gene, which encodes frataxin, leading to reduced expression of frataxin, a mitochondrial protein essential for cellular homeostasis. Frataxin deficiency results in oxidative stress and mitochondrial dysfunction and impaired redox balance. Currently, there is no cure for FRDA. This study aimed to evaluate the therapeutic potential of antioxidants dimethyl fumarate (DMF), N-acetylcysteine (NAC), and L-ascorbic acid (LAA) in restoring mitochondrial redox homeostasis and frataxin levels in FRDA patient-derived fibroblasts and 2D sensory neurons. We assessed cell viability, mitochondrial and cellular reactive oxygen species (ROS) levels, mitochondrial DNA copy number, mitochondrial membrane potential, and frataxin and NRF2 expression at both mRNA and protein levels following antioxidant treatment, either individually or in combination. Treatment with LAA, NAC, and DMF resulted in significant reductions in mitochondrial and cellular ROS, along with increased FXN and NRF2 expression, and enhanced NRF2 nuclear translocation. Furthermore, these compounds improved aconitase/citrate synthase activity, GSH/GSSG ratios, and mitochondrial membrane potential. Notably, the combination of LAA and NAC consistently alleviated multiple disease-associated defects in FRDA cells, suggesting its potential as a promising therapeutic approach.

Friedreich's ataxia (FA) is a genetic disorder caused by a severe decrease in FXN (frataxin) protein expression in mitochondria. The clinical manifestation of this disorder is a cerebellar ataxia; however, the common lethal component in FA is cardiomyopathy.

A conditional Fxnflox/null::MCK-Cre knockout (FXN-cKO) mouse model was used to mimic the late-stage severe cardiomyopathy in FA. Nrf2 (nuclear factor erythroid 2-related factor 2) inducers, omaveloxolone and dimethyl fumarate (DMF), were independently tested in this mouse model to determine the effects on cardiac health and lifespan.

Omaveloxolone significantly improved cardiac contractile function and markers of heart failure in FA such as Nppb, Aldh1a3, and Gdf15. Despite improvement in cardiac function, omaveloxolone did not prevent premature death in FXN-cKO animals and notably accelerated death in FXN-cKO females. Omaveloxolone decreased oxidative stress and inflammatory marker IL1β (interleukin-1 beta), and stimulated Nqo1 gene expression above control level. DMF restored elevated HO-1 (Hmox) expression and significantly increased Sirt1 expression. Although both omaveloxolone and DMF restored decreased SERCA2 (Atp2a) and MCU (Mcu) expression and ameliorated elevated phosphorylation of CaMKIIδ at Thr286 site in FA hearts, DMF did not improve cardiac contractile function and survival. Furthermore, neither omaveloxolone or DMF decreased hypertrophy and fibrosis (Masson trichrome staining and Lgals3 expression) or rescued impaired mitochondrial function and integrative stress response in FXN-cKO hearts.

These data demonstrate that omaveloxolone significantly improved contractile function but not survival in FA hearts because cardiac fibrosis and wall stress persisted even with omaveloxolone treatment. More studies are warranted to determine the cause of premature death in omaveloxolone-treated FXN-cKO female mice.

Expansion of a disease-specific tandem repeat is responsible for >45 Repeat Expansion Diseases (REDs). The expansion mutation in each of these diseases has different pathological consequences and most are currently incurable. If the underlying mechanism of mutation is shared, a strategy that slows repeat expansion in one RED may be applicable to multiple REDs. However, the fact that PMS2, a component of the MutLα mismatch repair complex, promotes expansion in some models and protects against it in others, suggests that the expansion mechanisms may differ. We show here using mouse models of two REDs caused by different repeats that the seemingly paradoxical effects of PMS2 do not reflect different expansion mechanisms but rather cell-type and dosage effects in different tissues. This differential effect is recapitulated in mouse embryonic stem cells with inducible PMS2 expression: PMS2 promotes expansion at low concentrations, an effect that requires a functional nuclease domain; while at higher concentrations it protects against expansion. The apparent paradoxical behavior of PMS2 can be resolved in a model based on the different in vitro cleavage preferences of MutLα and MutLγ, another MutL complex known to be required for expansion. Our data thus resolve a longstanding puzzle and suggest a common mechanism responsible for REDs. Our data also provide proof of concept that increasing PMS2 levels suppresses repeat expansion not only in cells where its loss promotes expansion, but also in cells that require it for expansion, supporting its potential as a broadly applicable therapeutic strategy.

Collectively the Repeat Expansion Diseases (REDs) represent a significant health burden. Since the consequences of the expansion mutation differ across diseases, therapeutic approaches that block the underlying mutation are appealing, particularly if the mechanism is shared. However, the conflicting effects of PMS2 loss in different REDs models challenges this idea. Here we show using two different REDs models that these disparate effects can be reconciled into a single model of repeat expansion, thus increasing confidence that the REDs do all share a common mutational mechanism. Importantly, we show that elevating PMS2 levels suppresses repeat expansion in multiple cellular contexts, including those in which PMS2 is normally required for expansion, demonstrating its potential as a broadly applicable therapeutic strategy for REDs.

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder characterized by ataxia, sensory loss and pyramidal signs. While the majority of FRDA cases are caused by biallelic GAA trinucleotide repeat expansions in intron 1 of FXN, there is a subset of patients harboring a heterozygous pathogenic small variant compound-heterozygous with a GAA repeat expansion. We report on the diagnostic journey of a 21-year-old patient who was clinically suspected of having FRDA at the age of 12 years. Genetic testing included fragment analysis, gene panel analysis and exome sequencing, which only detected one pathogenic heterozygous missense variant (c.389 G>T,p.Gly130Val) in FXN. Although conventional repeat analyses failed to detect GAA expansions in our patient, subsequent short-read genome sequencing (GS) indicated a potential GAA repeat expansion. This finding was confirmed by long-read GS, which in addition revealed a complex pattern of interruptions. Both large and small GAA expansions with divergent interruptions containing G, A, GA, GAG and/or GAAG sequences were present within one allele, indicating mosaic sequence variations. Our findings underscore the complexity of repeat expansions which can exhibit both interruptions and somatic instability. We also highlight the utility of long-read GS in unraveling intricate genetic profiles, ultimately contributing to more accurate diagnoses in clinical practice.

Friedreich ataxia (FRDA) is a rare, inherited progressive movement disorder for which there is currently no cure. The field urgently requires more sensitive, objective, and clinically relevant biomarkers to enhance the evaluation of treatment efficacy in clinical trials and to speed up the process of drug discovery. This study pioneers the development of clinically relevant, multidomain, fully objective composite biomarkers of disease severity and progression, using multimodal neuroimaging and background data (i.e., demographic, disease history, genetics). Data from 31 individuals with FRDA and 31 controls from a longitudinal multimodal natural history study IMAGE-FRDA, were included. Using an elasticnet predictive machine learning (ML) regression model, we derived a weighted combination of background, structural MRI, diffusion MRI, and quantitative susceptibility imaging (QSM) measures that predicted Friedreich ataxia rating scale (FARS) with high accuracy (R2 = 0.79, root mean square error (RMSE) = 13.19). This composite also exhibited strong sensitivity to disease progression over two years (Cohen's d = 1.12), outperforming the sensitivity of the FARS score alone (d = 0.88). The approach was validated using the Scale for the assessment and rating of ataxia (SARA), demonstrating the potential and robustness of ML-derived composites to surpass individual biomarkers and act as complementary or surrogate markers of disease severity and progression. However, further validation, refinement, and the integration of additional data modalities will open up new opportunities for translating these biomarkers into clinical practice and clinical trials for FRDA, as well as other rare neurodegenerative diseases.

This study explores the utility of various evoked fields in elucidating the pathophysiology of Friedreich's ataxia (FA) and potentially contributing to developing more targeted diagnostic and therapeutic strategies.

Thirty-seven patients with FA aged 27.6 ± 7.4 years and a control group of 17 healthy subjects were enrolled in the study. The neuromagnetic response to auditory, tactile, visual, somatosensory, auditory and tactile oddball stimulation were acquired. For all the components of interest, latency and amplitude were measured and correlated with clinical data.

Neuromagnetic responses were identifiable in more than 90% of cases. A significant response delay was observed in all tested modalities (auditory, somatosensory, tactile and visual responses). P300 responses were comparable in patients and healthy subjects. Latencies of visual and auditory responses correlated with SARA scores. Moreover, latencies of auditory responses correlated with disease onset age, whereas latencies of visual responses correlated with disease severity.

Auditory and visual responses correlated with the severity of the disease, whereas alterations in somatosensory responses represent an intrinsic characteristic of the disease.

In FA the study of evoked visual fields could provide a possible biomarker of disease progression and treatment efficacy.

Repetitive DNA is a feature of all organisms, ranging from archaea and plants to humans. DNA repeats can be seen both in coding and in noncoding regions of the genome. Due to the recurring nature of the sequences, simple DNA repeats tend to be more prone to errors during replication and repair, resulting in variability in their unit length. This feature of simple sequence repeats led to their use as molecular markers for mapping traits in diverse organisms. Advances in genomics, and the ever-reducing costs of genome sequencing have empowered us to assess the functional impacts of DNA repeats. The variability in repeat lengths can cause phenotypic differences depending on where they are present in the genome. Variability in the repeat length in coding regions of genes results in poly amino acid stretches that appear to interfere with protein function, including the perturbation of protein-protein interactions with diverse phenotypic impacts. These are often common allelic variations that can significantly impact evolutionary dynamics. In extreme situations, repeats can undergo massive expansions and appear as outliers. Repeat expansions underlie several genetic defects in plants to diseases in humans. This review systematically analyses tandem DNA repeats in plants, their role in development and environmental response and adaptation in plants. We identify and synthesise emerging themes, differentiate repeat length variability and repeat expansions, and argue that many repeat-associated phenotypes in plants are yet to be discovered. We emphasise the underexplored nature and immense potential of this area of research, particularly in plants, and suggest ways in which this can be achieved and how it might contribute to evolution and agricultural productivity.

Repeat-induced epigenetic changes are observed in many repeat expansion disorders (REDs). These changes result in transcriptional deficits and/or silencing of the associated gene. MSH2, a mismatch repair protein that is required for repeat expansion in the REDs, has been implicated in the maintenance of DNA methylation seen in the region upstream of the expanded CTG repeats at the DMPK locus in myotonic dystrophy type 1 (DM1). Here, we investigated the role of MSH2 in aberrant DNA methylation in two additional REDs, fragile X syndrome (FXS) that is caused by a CGG repeat expansion in the 5' untranslated region (UTR) of the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene, and Friedreich's ataxia (FRDA) that is caused by a GAA repeat expansion in intron 1 of the frataxin (FXN) gene.

In contrast to what is seen at the DMPK locus in DM1, loss of MSH2 did not decrease DNA methylation at the FMR1 promoter in FXS embryonic stem cells (ESCs) or increase FMR1 transcription. This difference was not due to the differences in the CpG density of the two loci as a decrease in DNA methylation was also not observed in a less CpG dense region upstream of the expanded GAA repeats in the FXN gene in MSH2 null induced pluripotent stem cells (iPSCs) derived from FRDA patient fibroblasts. Surprisingly, given previous reports, we found that FMR1 reactivation was associated with a high frequency of MSH2-independent CGG-repeat contractions that resulted a permanent loss of DNA methylation. MSH2-independent GAA-repeat contractions were also seen in FRDA cells.

Our results suggest that there are mechanistic differences in the way that DNA methylation is maintained in the region upstream of expanded repeats among different REDs even though they share a similar mechanism of repeat expansion. The high frequency of transcription-induced MSH2-dependent and MSH2-independent contractions we have observed may contribute to the mosaicism that is frequently seen in carriers of FMR1 alleles with expanded CGG-repeat tracts. These contractions may reflect the underlying problems associated with transcription through the repeat. Given the recent interest in the therapeutic use of transcription-driven repeat contractions, our data may have interesting mechanistic, prognostic, and therapeutic implications.

Friedreich's Ataxia (FA) is a rare, inherited ataxia resulting from GAA triplet expansions in the first intron of the Frataxin (FXN) gene, which encodes a mitochondrial protein involved in the incorporation of iron into iron-sulfur clusters. We previously identified decreased levels of F-actin and tight junction (TJ) proteins, which coincided with paracellular permeability in an FXN shRNA-mediated knockdown immortalized human brain microvascular endothelial cell (BMVEC) model. This premise is underexplored in the FA literature, prompting us to confirm these findings using a patient-derived iPSC model. One line each of FA patient iPSCs and age- and sex-matched apparently healthy iPSCs were differentiated into BMVEC-like cells. We quantified actin glutathionylation, F-actin abundance, TJ expression and organization, and barrier integrity. In the absence of dysregulated F-actin organization, FA iBMVEC exhibited a loss of 50% ZO-1, 63% Occludin, and 19% Claudin-5 protein expression, along with a disruption in the bi-cellular organization of the latter two proteins. Functionally, this correlated with barrier hyperpermeability, delayed barrier maturation, and increased flux of the fluorescent tracer Lucifer Yellow. These data indicate that decreased barrier integrity is a pathophysiological phenotype of FA brain microvascular endothelial cells. Clinically, this may represent a targetable pathway to reduce brain iron accumulation, neuroinflammation, and neurodegeneration profiles in FA. Additionally, an investigation into other barrier systems, such as the blood-nerve barrier, blood-CSF barrier, or cardiac vasculature, may provide insights into the extra-neural symptoms experienced by FA patients.

TRACK is a user-friendly Snakemake workflow designed to streamline the discovery and comparison of tandem repeats (TRs) across species. TRACK facilitates the cataloging and filtering of TRs based on reference genomes or T2T transcripts, and applies reciprocal LiftOver and sequence alignment methods to identify putative homologous TRs between species. For further analyses, TRACK can be used to genotype TRs and subsequently estimate and plot basic population genetic statistics. By incorporating key functionalities within an integrated workflow, TRACK enhances TR analysis accessibility and reproducibility, while offering flexibility for the user.

The TRACK toolkit with step-by-step tutorial is freely available at https://github.com/caroladam/track.

Spinocerebellar ataxia 27B (SCA27B) is a common autosomal dominant ataxia caused by an intronic GAA•TTC repeat expansion in FGF14. Neuropathological studies have shown that neuronal loss is largely restricted to the cerebellum. Although the repeat locus is highly unstable during intergenerational transmission, it remains unknown whether it exhibits cerebral mosaicism and progressive instability throughout life. We conducted an analysis of the FGF14 GAA•TTC repeat somatic instability across 156 serial blood samples from 69 individuals, fibroblasts, induced pluripotent stem cells and post-mortem brain tissues from six controls and six patients with SCA27B, alongside methylation profiling using targeted long-read sequencing. Peripheral tissues exhibited minimal somatic instability, which did not significantly change over periods of more than 20 years. In post-mortem brains, the GAA•TTC repeat was remarkably stable across all regions, except in the cerebellar hemispheres and vermis. The levels of somatic expansion in the cerebellar hemispheres and vermis were, on average, 3.15 and 2.72 times greater relative to other examined brain regions, respectively. Additionally, levels of somatic expansion in the brain increased with repeat length and tissue expression of FGF14. We found no significant difference in methylation of wild-type and expanded FGF14 alleles in post-mortem cerebellar hemispheres between patients and controls. In conclusion, our study revealed that the FGF14 GAA•TTC repeat exhibits a cerebellar-specific expansion bias, which may explain the pure cerebellar involvement in SCA27B.

Friedreich ataxia (FRDA) is a rare multisystem, life-limiting disease and is the most common early-onset inherited ataxia in populations of European, Arab and Indian descent. In recent years, substantial progress has been made in dissecting the pathogenesis and natural history of FRDA, and several clinical trials have been initiated. A particularly notable recent achievement was the approval of the nuclear factor erythroid 2-related factor 2 activator omaveloxolone as the first disease-specific therapy for FRDA. In light of these developments, we review milestones in FRDA translational and clinical research over the past 10 years, as well as the various therapeutic strategies currently in the pipeline. We also consider the lessons that have been learned from failed trials and other setbacks. We conclude by presenting a global roadmap for future research, as outlined by the recently established Friedreich's Ataxia Global Clinical Consortium, which covers North and South America, Europe, India, Australia and New Zealand.

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by frataxin deficiency. Neurological deficits remain the ubiquitous feature of FRDA and include progressive ataxia and dysarthria, both of which are controlled to a large degree by the cerebellum. The precise impact of frataxin deficiency on the cerebellum including Purkinje cells remains unclear. In the present work, we examined the biochemical and structural properties of the cerebellum and Purkinje cells in the doxycycline-inducible (FRDAkd) and the Knock-in/Knockout (KIKO) mouse models of FRDA. Acute systemic knockdown of frataxin in FRDAkd mice and chronic frataxin deficiency in KIKO leads to a significant decrease in levels of AMPA receptors, particularly GluR2, and an increase in glial glutamate transporters. Significant astroglial accumulation occurred in KIKO cerebellum but not in FRDAkd mice. Purkinje cell dendritic arbors in the molecular layer did not change compared to wildtype in either model. The Purkinje cell postsynaptic receptor NMDAR1 significantly decreased only in the FRDAkd cerebellum while other NMDA receptor subunits, largely found in non-Purkinje cells, did not change. Overall, we observed dysregulated levels of glutamate receptors and transporters in the KIKO and FRDAkd mice models of Friedreich ataxia, suggesting the importance of frataxin in maintaining Purkinje cells and cerebellar integrity along with synaptic properties. These results point to conserved but not identical synaptic features between the models that may represent markers or conceivably targets in human FRDA.

Mitochondrial functionality and cellular iron homeostasis are closely intertwined. Mitochondria are biosynthetic hubs for essential iron cofactors such as iron-sulfur (Fe-S) clusters and heme. These cofactors, in turn, enable key mitochondrial pathways, such as energy and metabolite production. Mishandling of mitochondrial iron is associated with a spectrum of human pathologies ranging from rare genetic disorders to common conditions. Here, we review mitochondrial iron utilization and its intersection with disease.

Friedreich's ataxia, a recessive disorder caused by a mutation in the frataxin (FXN) gene, has few mouse models that demonstrate a progressive behavioral decline paralleling that of patients. A mouse model of systemic frataxin deficiency, the FXNKD, was recently developed using a doxycycline-inducible method; it is thought to mimic the patient phenotype seen when frataxin levels are decreased, but it has not been determined whether it is reliable for assessment of therapeutics. FXNKD mice underwent testing for 12 weeks alongside littermates, undergoing tests of motor function, gait and sensation. Additionally, a subset underwent treatment with omaveloxolone or dimethyl fumarate, both NRF2 inducers. We identified multiple techniques that sensitively detect decline in the mice, including open field, gait analysis and Von Frey tests. Furthermore, we developed a novel Salinas-Montgomery ataxia scale, which allows for more comprehensive assessment than a four-part cerebellar ataxia scale. Despite validating multiple sensitive techniques, we did not see any benefits of NRF2-inducing therapies in any tests. This was exacerbated by the discovery of a sexual dimorphism in FXNKD mice, in which males show more significant decline and better responsiveness to NRF2-inducing therapeutics.

Friedreich's ataxia (FRDA) affects both the central and peripheral nervous system. Peripheral nerve involvement manifests predominantly as a progressive sensory neuropathy caused by dorsal root ganglionopathy. An additional direct involvement of peripheral nerves leading to abnormal myelination is increasingly discussed. Here, we characterize lower extremity peripheral nerve involvement in FRDA by quantitative magnetic resonance neurography (MRN).

Sixteen genetically confirmed FRDA patients and 16 age-/sex-matched controls were prospectively enrolled. Patients underwent neurologic examinations and nerve conduction studies (NCS). Large-coverage MRN of sciatic and tibial nerves was conducted utilizing dual-echo turbo-spin-echo sequences with spectral fat saturation for T2-relaxometry, and two gradient-echo sequences with and without off-resonance saturation rapid frequency pulses for magnetization transfer contrast imaging. Microstructural and morphometric MRN markers including T2-relaxation time (T2app), proton spin density (ρ), magnetization transfer ratio (MTR), and cross-sectional area (CSA) were calculated to characterize nerve lesions.

Tibial nerve ρ and T2app were markedly decreased in FRDA at the thigh (ρ: 368.4 ± 11.0 a.u.; T2app: 59.5 ± 1.8 ms) and lower leg (ρ: 337.3 ± 12.6 a.u.; T2app: 53.9 ± 1.4 ms) versus controls (thigh, ρ: 458.9 ± 9.5 a.u., p < 0.0001; T2app: 66.3 ± 0.8 ms, p = 0.0019; lower leg, ρ: 449.9 ± 12.1 a.u., p < 0.0001; T2app: 62.4 ± 1.2 ms, p < 0.0001) and correlated well with clinical scores, disease duration, and NCS. MTR and CSA did not differentiate between FRDA and controls.

Our study results provide a profound characterization of peripheral nerve involvement in FRDA. The identified good correlation between ρ and T2app with clinical symptom scores and NCS suggests that parameters of T2 relaxometry may become relevant biomarkers to monitor disease progression and therapeutic responses in potential future clinical trials.

Friedreich's Ataxia (FRDA) is a neurodegenerative disease that affects a variety of different organ systems. The disease is caused by GAA repeat expansions in intron 1 of the Frataxin gene (FXN), which results in a decrease in the expression of the FXN protein. FXN is needed for the biogenesis of iron-sulfur clusters (ISC) which are required by key metabolic processes in the mitochondria. Without ISCs those processes do not occur properly. As a result, reactive oxygen species accumulate, and the mitochondria cease to function. Iron is also thought to accumulate in the cells of certain tissue types. These processes are thought to be intimately related to the pathologies affecting a myriad of tissues in FRDA. Most FRDA patients suffer from loss of motor control, cardiomyopathy, scoliosis, foot deformities, and diabetes. In this review, we discuss the known features of FRDA pathology and the current understanding about the basis of these alterations.

Iron-sulfur clusters are essential protein cofactors synthesized in human mitochondria by an NFS1-ISD11-ACP-ISCU2-FXN assembly complex. Surprisingly, researchers have discovered three distinct quaternary structures for cysteine desulfurase subcomplexes, which display similar interactions between NFS1-ISD11-ACP protomeric units but dramatically different dimeric interfaces between the protomers. Although the role of these different architectures is unclear, possible functions include regulating activity and promoting the biosynthesis of distinct sulfur-containing biomolecules. Here, crystallography, native ion-mobility mass spectrometry, and chromatography methods reveal the Fe-S assembly subcomplex exists as an equilibrium mixture of these different quaternary structures. Isotope labeling and native mass spectrometry experiments show that the NFS1-ISD11-ACP complexes disassemble into protomers, which can then undergo exchange reactions and dimerize to reform native complexes. Single crystals isolated in distinct architectures have the same activity profile and activation by the Friedreich's ataxia (FRDA) protein frataxin (FXN) when rinsed and dissolved in assay buffer. These results suggest FXN functions as a "molecular lock" and shifts the equilibrium toward one of the architectures to stimulate the cysteine desulfurase activity and promote iron-sulfur cluster biosynthesis. An NFS1-designed variant similarly shifts the equilibrium and partially replaces FXN in activating the complex. We propose that eukaryotic cysteine desulfurases are unusual members of the morpheein class of enzymes that control their activity through their oligomeric state. Overall, the findings support architectural switching as a regulatory mechanism linked to FXN activation of the human Fe-S cluster biosynthetic complex and provide new opportunities for therapeutic interventions of the fatal neurodegenerative disease FRDA.

Most disorders of steroidogenesis, such as forms of congenital adrenal hyperplasia (CAH) are caused by mutations in genes encoding the steroidogenic enzymes and are often recognized clinically by cortisol deficiency, hyper- or hypo-androgenism, and/or altered mineralocorticoid function. Most steroidogenic enzymes are forms of cytochrome P450. Most P450s, including several steroidogenic enzymes, are microsomal, requiring electron donation by P450 oxidoreductase (POR); however, several steroidogenic enzymes are mitochondrial P450s, requiring electron donation via ferredoxin reductase (FDXR) and ferredoxin (FDX). POR deficiency is a rare but well-described form of CAH characterized by impaired activity of 21-hydroxylase (P450c21, CYP21A2) and 17-hydroxylase/17,20-lyase (P450c17, CYP17A1); more severely affected individuals also have the Antley-Bixler skeletal malformation syndrome and disordered genital development in both sexes, and hence is easily recognized. The 17,20-lyase activity of P450c17 requires both POR and cytochrome b5 (b5), which promote electron transfer. Mutations of POR, b5, or P450c17 can cause selective 17,20-lyase deficiency. In addition to providing electrons to mitochondrial P450s, FDX, and FDXR are required for the synthesis of iron-sulfur clusters, which are used by many enzymes. Recent work has identified FDXR mutations in patients with visual impairment, optic atrophy, neuropathic hearing loss, and developmental delay, resembling the global neurologic disorders seen with mitochondrial diseases. Many of these patients have had life-threatening events or deadly infections, often without an apparent triggering event. Adrenal insufficiency has been predicted in such individuals but has only been documented recently. Neurologists, neonatologists, and geneticists should seek endocrine assistance in evaluating and treating patients with mutations in FDXR.

Friedreich ataxia (FRDA) is an autosomal recessive disorder caused by GAA expansions in the FXN gene, which codes for the protein frataxin (FXN). These mutations reduce FXN expression, leading to mitochondrial dysfunction and multisystemic disease. Accumulating evidence suggests that neuronal dysfunction, rather than neuronal death, may drive the neurological phenotypes of FRDA, but the mechanisms underlying such neurological phenotypes remain unclear. To investigate the neural circuit basis of this dysfunction, we employed field recordings to measure Purkinje cell (PC) function and synaptic properties along with western blotting and immunohistochemistry to determine their density and structure in two established FRDA mouse models, the shRNA-frataxin (FRDAkd) and the frataxin knock in-knockout (KIKO) mice. Western blotting demonstrated subtle changes in mitochondrial proteins and only a modest reduction in the density of calbindin positive cells PCs in the cerebellar cortex of the FRDAkd mice, with no change in the density of PCs in the KIKO mice. Though PC density differed slightly in the two models, field recordings of parallel fiber-PC synapses in the molecular layer demonstrated concordant hypo-excitability of basal synaptic transmission and impairments of long-term plasticity using induction protocols associated with both potentiation and depression of synaptic strength. These results indicate that synaptic instability might be a common feature in FRDA mouse models.

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.

Friedreich ataxia (FRDA) is a slowly progressive neurological disease resulting from decreased levels of the protein frataxin, a small mitochondrial protein that facilitates the synthesis of iron-sulfur clusters in the mitochondrion. It is caused by GAA (guanine-adenine-adenine) repeat expansions in the FXN gene in 96% of patients, with 4% of patients carrying other mutations (missense, nonsense, deletion) in the FXN gene. Compound heterozygote patients with one expanded GAA allele and a non-GAA repeat mutation can have subtle differences in phenotype from typical FRDA, including, in patients with selected missense mutations, both more severe features and less severe features in the same patient. In this review, we propose explanations for such phenotypes based on the potential for activities of frataxin other than enhancement of iron-sulfur cluster synthesis, as well as crucial future experiments for fully understanding the role of frataxin in cells.

In the late 1800s, Nikolaus Friedreich first described "degenerative atrophy of the posterior columns of the spinal cord," noting its connection to progressive ataxia, sensory loss, and muscle weakness, now recognized as Friedreich ataxia (FRDA). Renewed interest in the disease in the 1970s and 80s by the Quebec Cooperative Group and by Anita Harding led to the development of clinical diagnostic criteria and insights into associated biochemical abnormalities, although the primary defect remained unknown. In 1988, Susan Chamberlain mapped FRDA's location on chromosome 9. In the early 90s, collaborative research, including work by the author's team, identified a gene, later named FXN, containing an expanded GAA repeat-confirming it as the FRDA mutation. This discovery established a diagnostic foundation for FRDA, advancing genetic testing and opening new research avenues. These new areas of study included the characteristics, origin, and pathogenicity of the GAA repeat expansion; the characterization of frataxin, the encoded protein, including its subcellular localization, structure, and function; the identification of cellular pathways disrupted by frataxin deficiency; and the redefinition of FRDA phenotypes based on genetic testing, along with the study of FRDA's natural history. In addition, efforts focused on the search for biomarkers to reflect diagnosis, disease severity, and progression and, most importantly, the identification and development of therapeutic approaches in both preclinical and clinical settings. The creation of cellular and animal models was crucial to this progress, as was the formation of consortia to collaboratively drive basic and clinical research forward. Now, 28 years after the gene discovery, although much remains to be understood about the disease's mechanisms and the development of effective therapies, the progress is undeniable. A thriving community has emerged, uniting researchers, health care providers, industry professionals, individuals with FRDA, their families, and dedicated volunteers. With this collective effort, a cure is within reach.

Central nervous system (CNS) diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), spinal cord injury (SCI), and ischemic strokes and certain rare diseases, such as amyotrophic lateral sclerosis (ALS) and ataxia, present significant obstacles to treatment using conventional molecular pharmaceuticals. Gene therapy, with its ability to target previously "undruggable" proteins with high specificity and safety, is increasingly utilized in both preclinical and clinical research for CNS ailments. As our comprehension of the pathophysiology of these conditions deepens, gene therapy stands out as a versatile and promising strategy with the potential to both prevent and treat these diseases. Despite the remarkable progress in refining and enhancing the structural design of gene therapy agents, substantial obstacles persist in their effective and safe delivery within living systems. To surmount these obstacles, a diverse array of gene delivery systems has been devised and continuously improved. Notably, Adeno-Associated Virus (AAVs)-based viral gene vectors and lipid-based nanocarriers have each advanced the in vivo delivery of gene therapies to various extents. This review aims to concisely summarize the pathophysiological foundations of CNS diseases and to shed light on the latest advancements in gene delivery vector technologies. It discusses the primary categories of these vectors, their respective advantages and limitations, and their specialized uses in the context of gene therapy delivery.

Autosomal dominant cerebellar ataxias, also known as spinocerebellar ataxias (SCAs), are genetically and clinically diverse neurodegenerative disorders characterized by progressive cerebellar dysfunction. Despite advances in sequencing technologies, a large proportion of patients with SCA still lack a definitive genetic diagnosis. The advent of advanced bioinformatic tools and emerging genomics technologies, such as long-read sequencing, offers an unparalleled opportunity to close the diagnostic gap for hereditary ataxias. This article reviews the recently identified repeat expansion SCAs and describes their molecular basis, epidemiology, and clinical features.

Leveraging advanced bioinformatic tools and long-read sequencing, recent studies have identified novel pathogenic short tandem repeat expansions in FGF14, ZFHX3, and THAP11, associated with SCA27B, SCA4, and SCA51, respectively. SCA27B, caused by an intronic (GAA)•(TTC) repeat expansion, has emerged as one of the most common forms of adult-onset hereditary ataxias, especially in European populations. The coding GGC repeat expansion in ZFHX3 causing SCA4 was identified more than 25 years after the disorder's initial clinical description and appears to be a rare cause of ataxia outside northern Europe. SCA51, caused by a coding CAG repeat expansion, is overall rare and has been described in a small number of patients. The recent identification of three novel pathogenic repeat expansions underscores the importance of this class of genomic variation in the pathogenesis of SCAs. Progress in sequencing technologies holds promise for closing the diagnostic gap in SCAs and guiding the development of therapeutic strategies for ataxia.

Historically, Friedreich's Ataxia (FRDA) has been linked to a relatively preserved cerebellar cortex. Recent advances in neuroimaging have revealed altered cerebello-cerebral functional connectivity (FC), but the extent of intra-cerebellar FC changes and their impact on cognition remains unclear. This study investigates intra-cerebellar FC alterations and their cognitive implications in FRDA. In this cross-sectional, single-center study, resting-state functional MRI data from 17 patients with FRDA (average age 27.7 ± 13.6 years; F/M = 6/11) and 20 healthy controls (HC) (average age 29.4 ± 9.7 years; F/M = 9/11), all of whom underwent neuropsychological testing, were analyzed. From functional connectivity matrices, graph measures were computed at both the network and node levels using two complementary parcellations. FRDA patients exhibited decreased global efficiency (p = 0.04), nodal degree (p = 0.001) and betweenness centrality (p = 0.04) in the vermal portion of lobule VIII, along with reduced global efficiency in cerebellar regions belonging to the Control-A network (p = 0.02), one of the three subdivisions of the Frontoparietal network. Verbal memory deficits correlated with global efficiency in both the vermal portion of lobule VIII (r = 0.53, p = 0.02) and the cerebellar regions of the Control-A network (r = 0.49, p = 0.05). Graph analysis revealed regional intra-cerebellar FC changes in FRDA, marked by reduced functional centrality in cerebellar regions of the vermis and responsible for executive functions. These changes correlated with cognitive alterations, highlighting the role of the cerebellar cortex in the cognitive impairment observed in FRDA.

Mitochondria are essential for cellular function and viability, serving as central hubs of metabolism and signaling. They possess various metabolic and quality control mechanisms crucial for maintaining normal cellular activities. Mitochondrial genetic disorders can arise from a wide range of mutations in either mitochondrial or nuclear DNA, which encode mitochondrial proteins or other contents. These genetic defects can lead to a breakdown of mitochondrial function and metabolism, such as the collapse of oxidative phosphorylation, one of the mitochondria's most critical functions. Mitochondrial diseases, a common group of genetic disorders, are characterized by significant phenotypic and genetic heterogeneity. Clinical symptoms can manifest in various systems and organs throughout the body, with differing degrees and forms of severity. The complexity of the relationship between mitochondria and mitochondrial diseases results in an inadequate understanding of the genotype-phenotype correlation of these diseases, historically making diagnosis and treatment challenging and often leading to unsatisfactory clinical outcomes. However, recent advancements in research and technology have significantly improved our understanding and management of these conditions. Clinical translations of mitochondria-related therapies are actively progressing. This review focuses on the physiological mechanisms of mitochondria, the pathogenesis of mitochondrial diseases, and potential diagnostic and therapeutic applications. Additionally, this review discusses future perspectives on mitochondrial genetic diseases.

Dominantly inherited intronic GAA repeat expansions in the fibroblast growth factor 14 gene have recently been shown to cause spinocerebellar ataxia 27B. Currently, the pathogenic threshold of (GAA)≥300 repeat units is considered highly penetrant, while (GAA)250-299 is likely pathogenic with reduced penetrance. This study investigated the frequency of the GAA repeat expansion and the phenotypic profile in a Cypriot cohort with unresolved late-onset cerebellar ataxia. We analysed this trinucleotide repeat in 155 patients with late-onset cerebellar ataxia and 227 non-neurological disease controls. The repeat locus was examined by long-range PCR followed by fragment analysis using capillary electrophoresis, agarose gel electrophoresis and automated electrophoresis. A comprehensive comparison of all three electrophoresis techniques was conducted. Additionally, bidirectional repeat-primed PCRs and Sanger sequencing were carried out to confirm the absence of any interruptions or non-GAA motifs in the expanded alleles. The (GAA)≥250 repeat expansion was present in 12 (7.7%) patients. The average age at disease onset was 60 ± 13.5 years. The earliest age of onset was observed in a patient with a (GAA)287 repeat expansion, with ataxia symptoms appearing at 25 years of age. All patients with spinocerebellar ataxia 27B displayed symptoms of gait and appendicular ataxia. Nystagmus was observed in 41.7% of the patients, while 58.3% exhibited dysarthria. Our findings indicate that spinocerebellar ataxia 27B represents the predominant aetiology of autosomal dominant cerebellar ataxia in the Cypriot population, as this is the first dominant repeat expansion ataxia type detected in this population. Given our results and existing research, we propose including fibroblast growth factor 14 GAA repeat expansion testing as a first-tier genetic diagnostic approach for patients with late-onset cerebellar ataxia.

Friedreich's ataxia (FRDA) is a neurodegenerative disorder characterized by severe neurological signs, affecting the peripheral and central nervous system, caused by reduced frataxin protein (FXN) levels. Although several studies have highlighted cellular dysfunctions in neurons, there is limited information on the effects of FXN depletion in astrocytes and on the potential non-cell autonomous mechanisms affecting neurons in FRDA. In this study, we generated a model of FRDA cerebellar astrocytes to unveil phenotypic alterations that might contribute to cerebellar atrophy. We treated primary cerebellar astrocytes with an RNA interference-based approach, to achieve a reduction of FXN comparable to that observed in individuals with FRDA. These FRDA-like astrocytes display some typical features of the disease, such as an increase of oxidative stress and a depletion of glutathione content. Moreover, FRDA-like astrocytes exhibit decreased Ca2+ responses to purinergic stimuli. Our findings shed light on cellular changes caused by FXN downregulation in cerebellar astrocytes, likely impairing their complex interaction with neurons. The potentially impaired ability to provide neuronal cells with glutathione or to release neuromodulators in a Ca2+-dependent manner could affect neuronal function, contributing to neurodegeneration.

Friedreich's Ataxia (FRDA) is the most common hereditary ataxia and is mainly caused by biallelic GAA repeat expansion in the FXN gene. Rare patients carrying FXN point mutations or intragenic deletions are reported. We describe the first FRDA patient with a chromosome 9 segmental Uniparental isoDisomy (UPiD) unmasking a homozygous FXN expansion initially undetected by TP-PCR. The child presented with a progressive proprioceptive ataxia associated with peripheral sensory neuronopathy and severe scoliosis. Whole genome sequencing (WGS) identified a maternal segmental Uniparental Isodisomy (UPiD) encompassing FXN. Short tandem repeats analysis on WGS showed a biallelic FXN expansion. The identification of a deletion in the primer-annealing region of the TP-PCR explained the initial TP-PCR failure. This is the first documented case of FRDA caused by segmental UPiD. This case highlights the complexity of the molecular diagnosis of FRDA, and emphasises the importance of integrating results from various technical diagnostic approaches.

Friedreich's ataxia (FRDA) is a multisystem, autosomal recessive disorder caused by mutations in the frataxin (FXN) gene. As FRDA is considered an FXN deficiency disorder, numerous therapeutic approaches in development or clinical trials aim to supplement FXN or restore endogenous FXN expression. These include gene therapy, protein supplementation, genome editing or upregulation of FXN transcription. To evaluate efficacy of these therapies, potency assays capable of quantitative determination of FXN biological activity are needed. Herein, we evaluate the suitability of mouse embryonic fibroblasts derived from Fxn G127V knockin mice (MUT MEFs) as a candidate for cell-based potency assays. We demonstrate that these cells, when immortalized, continue to express minute amounts of Fxn and exhibit a broad range of phenotypes that result from severe Fxn deficiency. Exogenous FXN supplementation reverses these phenotypes. Thus, immortalized MUT MEFs are an excellent tool for developing potency assays to validate novel FRDA therapies. Care needs to be exercised while utilizing these cell lines, as extended passaging results in molecular changes that spontaneously reverse FRDA-like phenotypes without increasing Fxn expression. Based on transcriptome analyses, we identified the Warburg effect as the mechanism allowing cells expressing a minimal level of Fxn to thrive under standard cell culture conditions.

Iron-sulfur (FeS) protein biogenesis in eukaryotes begins with the de novo assembly of [2Fe-2S] clusters by the mitochondrial core iron-sulfur cluster assembly (ISC) complex. This complex comprises the scaffold protein ISCU2, the cysteine desulfurase subcomplex NFS1-ISD11-ACP1, the allosteric activator frataxin (FXN) and the electron donor ferredoxin-2 (FDX2). The structural interaction of FDX2 with the complex remains unclear. Here, we present cryo-EM structures of the human FDX2-bound core ISC complex showing that FDX2 and FXN compete for overlapping binding sites. FDX2 binds in either a 'distal' conformation, where its helix F interacts electrostatically with an arginine patch of NFS1, or a 'proximal' conformation, where this interaction tightens and the FDX2-specific C terminus binds to NFS1, facilitating the movement of the [2Fe-2S] cluster of FDX2 closer to the ISCU2 FeS cluster assembly site for rapid electron transfer. Structure-based mutational studies verify the contact areas of FDX2 within the core ISC complex.

Trinucleotide repeats, including Friedreich's ataxia (GAA)n repeats, become pathogenic upon expansions during DNA replication and repair. Here, we show that deficiency of the essential replisome component Mcm10 dramatically elevates (GAA)n repeat instability in a budding yeast model by loss of proper CMG helicase interaction. Supporting this conclusion, live-cell microscopy experiments reveal increased replication fork stalling at the repeat in mcm10-1 cells. Unexpectedly, the viability of strains containing a single (GAA)100 repeat at an essential chromosomal location strongly depends on Mcm10 function and cellular RPA levels. This coincides with Rad9 checkpoint activation, which promotes cell viability, but initiates repeat expansions via DNA synthesis by polymerase δ. When repair is inefficient, such as in the case of RPA depletion, breakage of under-replicated repetitive DNA can occur during G2/M, leading to loss of essential genes and cell death. We hypothesize that the CMG-Mcm10 interaction promotes replication through hard-to-replicate regions, assuring genome stability and cell survival.

The number of GAA repeats in the FXN gene is a major but not sole determinant of the clinical presentation of Friedreich ataxia (FRDA). The objective of this study was to establish whether the length of the GAA repeat tract in the FGF14 gene, which is associated with another neurodegenerative disorder (SCA27B), affects the clinical presentation (age at onset, mFARS score) of patients with FRDA.

The number of GAA repeats in the FXN and FGF14 genes was determined using PCR in a cohort of 221 patients with FRDA. Next, we compared absolute lengths of the FGF14 GAAs with FXN GAAs, followed by correlative analyses to determine potential effects of FGF14 GAA length on age at onset and clinical presentation (mFARS) of FRDA.

We found no significant correlation between the size of the GAA repeats in FXN and FGF14 loci in our FRDA cohort. Moreover, the number of GAAs in FGF14 did not affect the clinical presentation of FRDA even in a small number of cases where a long FGF14 allele was present.

Despite both molecular and clinical similarities between FRDA and SCA27B, the length of the GAA repeats in the FGF14 gene, including potentially pathogenic alleles, did not influence the clinical presentation of FRDA.

Synthetic genome readers/regulators (SynGRs) are bifunctional molecules that are rationally designed to bind specific genomic sequences and engage cellular machinery that regulates the expression of targeted genes. The prototypical SynGR1 targets GAA trinucleotide repeats and recruits the BET family of transcriptional regulatory proteins via a flexibly tethered ligand, JQ1. This pan-BET ligand binds both tandem bromodomains of BET proteins (BD1 and BD2). Second-generation SynGRs, which substituted JQ1 with bromodomain-selective ligands, unexpectedly revealed that BD1-selective ligands failed to functionally engage BET proteins in living cells despite displaying the ability to bind BD1 in vitro. Mechanistically, recruiting a BET protein via BD1- or BD2-selective SynGRs should have resulted in indistinguishable functional outcomes. Here we report the conversion of inactive BD1-targeting SynGRs into functional gene regulators by a structure-guided redesign of the chemical linker that bridges the DNA-binding molecule to the highly selective BD1 ligand GSK778. The results point to an optimal zone for positioning the BD1-selective ligand for functional engagement of BET proteins on chromatin, consistent with the preferred binding of BD1 domains to distal acetyllysine residues on histone tails. The results not only resolve the mechanistic conundrum but also provide insight into domain-selective targeting and nuanced design of chemo probes and therapeutics.