Common Recessive Ataxia Research Articles

Sacsin levels in PBMCs: A diagnostic assay for SACS variants in peripheral blood cells - A PROSPAX study.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a common recessive ataxia that is still underdiagnosed worldwide. An easily accessible diagnostic biomarker might help to diagnostically confirm patients presenting SACS variants of unknown significance (VUS) or atypical phenotypes. To detect sacsin in peripheral blood mononuclear cells (PBMCs) and to validate its diagnostic biomarker quality to discriminate biallelic SACS patients (including patients with VUS and/or atypical phenotypes) against healthy controls, non-ARSACS spastic ataxia patients, and heterozygous SACS carriers. Sacsin protein levels in PBMCs were assessed in patients versus controls and validated in skin-derived fibroblasts. Patients with biallelic SACS variants - including patients with VUS and/or atypical phenotypes - showed loss of sacsin in PBMCs, with discriminative performance against healthy, heterozygous, and non-ARSACS controls. This included all investigated SACS missense variants. Also, C-terminal variants escaping nonsense-mediated decay, while not differing from controls in expression level, showed lower molecular weight in this assay. Assessing sacsin levels using PBMCs offers an easy, peripherally accessible diagnostic biomarker for ARSACS, with PBMCs being much less invasive and easier to handle than fibroblasts. Additionally, this might be a potential target-engagement blood biomarker for sacsin-increasing therapies. © 2024 International Parkinson and Movement Disorder Society.

A peptide derived from TID1S rescues frataxin deficiency and mitochondrial defects in FRDA cellular models.

Friedreich's ataxia (FRDA), the most common recessive inherited ataxia, results from homozygous guanine-adenine-adenine (GAA) repeat expansions in intron 1 of the FXN gene, which leads to the deficiency of frataxin, a mitochondrial protein essential for iron-sulphur cluster synthesis. The study of frataxin protein regulation might yield new approaches for FRDA treatment. Here, we report tumorous imaginal disc 1 (TID1), a mitochondrial J-protein cochaperone, as a binding partner of frataxin that negatively controls frataxin protein levels. TID1 interacts with frataxin both in vivo in mouse cortex and in vitro in cortical neurons. Acute and subacute depletion of frataxin using RNA interference markedly increases TID1 protein levels in multiple cell types. In addition, TID1 overexpression significantly increases frataxin precursor but decreases intermediate and mature frataxin levels in HEK293 cells. In primary cultured human skin fibroblasts, overexpression of TID1S results in decreased levels of mature frataxin and increased fragmentation of mitochondria. This effect is mediated by the last 6 amino acids of TID1S as a peptide made from this sequence rescues frataxin deficiency and mitochondrial defects in FRDA patient-derived cells. Our findings show that TID1 negatively modulates frataxin levels, and thereby suggests a novel therapeutic target for treating FRDA.

Clinical stage and plasma neurofilament concentration in adults with Friedreich ataxia

ObjectivesFriedreich Ataxia (FRDA) is the most common recessive ataxia disorder. Yet, little is known of the prevalence in Sweden. In the future, there may be effective disease-modifying therapies, and use of clinical rating scales as well as possible biomarkers in serum or cerebrospinal fluid may be of importance. We evaluated the axonal protein neurofilament light in plasma (p-NfL) as a possible biomarker for disease severity in FRDA. Materials & methodsWe searched for all possible genetically confirmed FRDA cases in the Västra Götaland Region (VGR) of Sweden, and investigated each patient clinically and obtained blood sample for analysis of p-NfL. ResultsWe found eight patients corresponding to 1/170.000 adults in the VGR, and 5 of these participated in the study. Three out of the five FRDA patients displayed a small or moderate increase in the p-NfL value, compared to the age-adjusted cut-offs for p-NfL established in the Clinical Neurochemistry Laboratory at our hospital. The two others were the oldest and most severely affected, displayed normal values according the cut-off values. The cohort is too small to make any statistically significant correlation between the five p-NfL values with regard to disease severity. ConclusionsFRDA is less prevalent in our region of Sweden than could be assumed. In concordance with previous studies from other authors, we find that p-NfL may be increased in patients with FRDA, but less so in older more clinically affected patients. Thus, we conclude that on an individual basis, p-NFL is of uncertain clinical value as a suitable biomarker.

Anodal Cerebellar Transcranial Direct Current Stimulation Reduces Motor and Cognitive Symptoms in Friedreich's Ataxia: A Randomized, Sham-Controlled Trial.

Friedreich Ataxia is the most common recessive ataxia with only one therapeutic drug approved solely in the United States. The aim of this work was to investigate whether anodal cerebellar transcranial direct current stimulation (ctDCS) reduces ataxic and cognitive symptoms in individuals with Friedreich's ataxia (FRDA) and to assess the effects of ctDCS on the activity of the secondary somatosensory (SII) cortex. We performed a single-blind, randomized, sham-controlled, crossover trial with anodal ctDCS (5 days/week for 1 week, 20 min/day, density current: 0.057 mA/cm2 ) in 24 patients with FRDA. Each patient underwent a clinical evaluation (Scale for the Assessment and Rating of Ataxia, composite cerebellar functional severity score, cerebellar cognitive affective syndrome scale) before and after anodal and sham ctDCS. Activity of the SII cortex contralateral to a tactile oddball stimulation of the right index finger was evaluated with brain functional magnetic resonance imaging at baseline and after anodal/sham ctDCS. Anodal ctDCS led to a significant improvement in the Scale for the Assessment and Rating of Ataxia (-6.5%) and in the cerebellar cognitive affective syndrome scale (+11%) compared with sham ctDCS. It also led to a significant reduction in functional magnetic resonance imaging signal at the SII cortex contralateral to tactile stimulation (-26%) compared with sham ctDCS. One week of treatment with anodal ctDCS reduces motor and cognitive symptoms in individuals with FRDA, likely by restoring the neocortical inhibition normally exerted by cerebellar structures. This study provides class I evidence that ctDCS stimulation is effective and safe in FRDA. © 2023 International Parkinson and Movement Disorder Society.

The Complex Genetic Landscape of Hereditary Ataxias in Turkey and Implications in Clinical Practice.

The genetic and epidemiological features of hereditary ataxias have been reported in several populations; however, Turkey is still unexplored. Due to high consanguinity, recessive ataxias are more common in Turkey than in Western European populations. To identify the prevalence and genetic structure of hereditary ataxias in the Turkish population. Our cohort consisted of 1296 index cases and 324 affected family members. Polymerase chain reaction followed by Sanger sequencing or fragment analysis were performed to screen for the trinucleotide repeat expansions in families with a dominant inheritance pattern, as well as in sporadic cases. The expansion in the frataxin (FXN) gene was tested in all autosomal recessive cases and in sporadic cases with a compatible phenotype. Whole-exome sequencing was applied to 251 probands, selected based on the family history, age of onset, and phenotype. Mutations in known ataxia genes were identified in 30% of 1296 probands. Friedreich's ataxia was found to be the most common recessive ataxia in Turkey, followed by autosomal recessive spastic ataxia of Charlevoix-Saguenay. Spinocerebellar ataxia types 2 and 1 were the most common dominant ataxias. Whole-exome sequencing was performed in 251 probands with an approximate diagnostic yield of 50%. Forty-eight novel variants were found in a plethora of genes, suggesting a high heterogeneity. Variants of unknown significance were discussed in light of clinical data. With the large sample size recruited across the country, we consider that our results provide an accurate picture of the frequency of hereditary ataxias in Turkey. © 2021 International Parkinson and Movement Disorder Society.

P8 - Mitochondria, Nrf2 and mTOR

Friedreich's ataxia (FA) is the most common recessive ataxia, and it's phenotype is clinically indistinguishable from AVED, a deficiency of Vitamin E transport. We were the first to show that Friedreich's patient cells are very sensitive to oxidative stress. Ultimately this defect appears to reside in a deficiency of the antioxidant pathway Nrf2, which is less active in Friedreich's patient cells, and in FA animal models. Perhaps as a result of this Nrf2 defect, there is increased inflammation in Friedreich's patient cells and mice. But as Nrf2 is not only important in antioxidant homeostasis, but also mitochondrial homeostasis, this was investigated in Friedreich's models and patients. We found that Friedreich's cells, mice, and even people have an approximately 40% mitochondrial biogenesis defect. A high-throughput screening campaign for drugs that rescued Friedreich's cells from death identified three Nrf2 inducers, which could be of benefit in human Friedreich's therapy. One of these drugs, dimethyl fumarate, was shown to dose-dependently increase mitochondrial biogenesis and function when dosed in cells, and to increase mitochondrial biogenesis in mouse and human tissues, with a mechanism that appears to require Nrf2. Thus there is an interplay between Nrf2, mitochondrial biogenesis, and antioxidant status. We observed in a particular cancer there are alterations of mitochondrial biogenesis, which appear to result from differential Nrf2 activity. These differences in mitochondrial number allow the selective killing of such cells by mitochondrial inhibitors and a novel category of mTOR inhibitors.

Current and Promising Therapies in Autosomal Recessive Ataxias.

Ataxia is clinically characterized by unsteady gait and imbalance. Cerebellar disorders may arise from many causes such as metabolic diseases, stroke or genetic mutations. The genetic causes are classified by mode of inheritance and include autosomal dominant, X-linked and autosomal recessive ataxias. Many years have passed since the description of the Friedreich's ataxia, the most common autosomal recessive ataxia, and mutations in many other genes have now been described. The genetic mutations mostly result in the accumulation of toxic metabolites which causes Purkinje neuron lost and eventual cerebellar dysfunction. Unfortunately, the recessive ataxias remain a poorly known group of diseases and most of them are yet untreatable. The aim of this review is to provide a comprehensive clinical profile and to review the currently available therapies. We overview the physiopathology, neurological features and diagnostic approach of the common recessive ataxias. The emphasis is also made on potential drugs currently or soon-to-be in clinical trials. For instance, promising gene therapies raise the possibility of treating differently Friedreich's ataxia, Ataxia-telangiectasia, Wilson's disease and Niemann-Pick disease in the next few years.

Chapter 9 - Repeat expansion diseases

More than 40 diseases, most of which primarily affect the nervous system, are caused by expansions of simple sequence repeats dispersed throughout the human genome. Expanded trinucleotide repeat diseases were discovered first and remain the most frequent. More recently tetra-, penta-, hexa-, and even dodeca-nucleotide repeat expansions have been identified as the cause of human disease, including some of the most common genetic disorders seen by neurologists. Repeat expansion diseases include both causes of myotonic dystrophy (DM1 and DM2), the most common genetic cause of amyotrophic lateral sclerosis/frontotemporal dementia (C9ORF72), Huntington disease, and eight other polyglutamine disorders, including the most common forms of dominantly inherited ataxia, the most common recessive ataxia (Friedreich ataxia), and the most common heritable mental retardation (fragile X syndrome). Here I review distinctive features of this group of diseases that stem from the unusual, dynamic nature of the underlying mutations. These features include marked clinical heterogeneity and the phenomenon of clinical anticipation. I then discuss the diverse molecular mechanisms driving disease pathogenesis, which vary depending on the repeat sequence, size, and location within the disease gene, and whether the repeat is translated into protein. I conclude with a brief clinical and genetic description of individual repeat expansion diseases that are most relevant to neurologists.

Early cerebellar deficits in mitochondrial biogenesis and respiratory chain complexes in the KIKO mouse model of Friedreich ataxia.

ABSTRACTFriedreich ataxia (FRDA), the most common recessive inherited ataxia, results from deficiency of frataxin, a small mitochondrial protein crucial for iron-sulphur cluster formation and ATP production. Frataxin deficiency is associated with mitochondrial dysfunction in FRDA patients and animal models; however, early mitochondrial pathology in FRDA cerebellum remains elusive. Using frataxin knock-in/knockout (KIKO) mice and KIKO mice carrying the mitoDendra transgene, we show early cerebellar deficits in mitochondrial biogenesis and respiratory chain complexes in this FRDA model. At asymptomatic stages, the levels of PGC-1α (PPARGC1A), the mitochondrial biogenesis master regulator, are significantly decreased in cerebellar homogenates of KIKO mice compared with age-matched controls. Similarly, the levels of the PGC-1α downstream effectors, NRF1 and Tfam, are significantly decreased, suggesting early impaired cerebellar mitochondrial biogenesis pathways. Early mitochondrial deficiency is further supported by significant reduction of the mitochondrial markers GRP75 (HSPA9) and mitofusin-1 in the cerebellar cortex. Moreover, the numbers of Dendra-labeled mitochondria are significantly decreased in cerebellar cortex, confirming asymptomatic cerebellar mitochondrial biogenesis deficits. Functionally, complex I and II enzyme activities are significantly reduced in isolated mitochondria and tissue homogenates from asymptomatic KIKO cerebella. Structurally, levels of the complex I core subunit NUDFB8 and complex II subunits SDHA and SDHB are significantly lower than those in age-matched controls. These results demonstrate complex I and II deficiency in KIKO cerebellum, consistent with defects identified in FRDA patient tissues. Thus, our findings identify early cerebellar mitochondrial biogenesis deficits as a potential mediator of cerebellar dysfunction and ataxia, thereby providing a potential therapeutic target for early intervention of FRDA.

SYNE1 ataxia is a common recessive ataxia with major non-cerebellar features: a large multi-centre study.

Mutations in the synaptic nuclear envelope protein 1 (SYNE1) gene have been reported to cause a relatively pure, slowly progressive cerebellar recessive ataxia mostly identified in Quebec, Canada. Combining next-generation sequencing techniques and deep-phenotyping (clinics, magnetic resonance imaging, positron emission tomography, muscle histology), we here established the frequency, phenotypic spectrum and genetic spectrum of SYNE1 in a screening of 434 non-Canadian index patients from seven centres across Europe. Patients were screened by whole-exome sequencing or targeted panel sequencing, yielding 23 unrelated families with recessive truncating SYNE1 mutations (23/434 = 5.3%). In these families, 35 different mutations were identified, 34 of them not previously linked to human disease. While only 5/26 patients (19%) showed the classical SYNE1 phenotype of mildly progressive pure cerebellar ataxia, 21/26 (81%) exhibited additional complicating features, including motor neuron features in 15/26 (58%). In three patients, respiratory dysfunction was part of an early-onset multisystemic neuromuscular phenotype with mental retardation, leading to premature death at age 36 years in one of them. Positron emission tomography imaging confirmed hypometabolism in extra-cerebellar regions such as the brainstem. Muscle biopsy reliably showed severely reduced or absent SYNE1 staining, indicating its potential use as a non-genetic indicator for underlying SYNE1 mutations. Our findings, which present the largest systematic series of SYNE1 patients and mutations outside Canada, revise the view that SYNE1 ataxia causes mainly a relatively pure cerebellar recessive ataxia and that it is largely limited to Quebec. Instead, complex phenotypes with a wide range of extra-cerebellar neurological and non-neurological dysfunctions are frequent, including in particular motor neuron and brainstem dysfunction. The disease course in this multisystemic neurodegenerative disease can be fatal, including premature death due to respiratory dysfunction. With a relative frequency of ∼5%, SYNE1 is one of the more common recessive ataxias worldwide.

Dysregulation of cellular iron metabolism in Friedreich ataxia: from primary iron-sulfur cluster deficit to mitochondrial iron accumulation.

Friedreich ataxia (FRDA) is the most common recessive ataxia in the Caucasian population and is characterized by a mixed spinocerebellar and sensory ataxia frequently associating cardiomyopathy. The disease results from decreased expression of the FXN gene coding for the mitochondrial protein frataxin. Early histological and biochemical study of the pathophysiology in patient's samples revealed that dysregulation of iron metabolism is a key feature of the disease, mainly characterized by mitochondrial iron accumulation and by decreased activity of iron-sulfur cluster enzymes. In the recent past years, considerable progress in understanding the function of frataxin has been provided through cellular and biochemical approaches, pointing to the primary role of frataxin in iron-sulfur cluster biogenesis. However, why and how the impact of frataxin deficiency on this essential biosynthetic pathway leads to mitochondrial iron accumulation is still poorly understood. Herein, we review data on both the primary function of frataxin and the nature of the iron metabolism dysregulation in FRDA. To date, the pathophysiological implication of the mitochondrial iron overload in FRDA remains to be clarified.

Routine Clinical Testing Underestimates Proprioceptive Deficits in Friedreich’s Ataxia

Friedreich's ataxia (FA) is the most common recessive ataxia in the Western world with degeneration of dorsal root ganglia neurons as its major neuropathological hallmark. The sensitivity of clinical tools commonly used for the assessment of the proprioceptive component of FA is currently unknown. We hypothesised that current clinical testing underestimates proprioceptive deficits in FA patients. Such an underestimation would hamper our understanding of the components of FA, the monitoring of disease progression, and the detection of deficits in the current advent of drug trials. We compared clinical tests for joint position sense (JPS) and vibration sense (VS) to a test of spatial position sense (SPS) that examines localisation of both hands across a horizontal 2D space. We tested 22 healthy controls to derive a cut-off for the SPS. Eleven patients with genetically confirmed FA participated in this study. All 11 FA patients were impaired in the SPS test. Two patients showed unimpaired JPS and VS. Two additional patients showed unimpaired JPS, while two other patients unimpaired VS. The SPS test was more sensitive and revealed deficits potentially earlier than clinical screening tests. Only the SPS showed a positive correlation with ataxia severity. The SPS was more sensitive than the commonly used JPS and VS. Thus, our results indicate that proprioceptive deficits in FA start earlier and are more severe than indicated by routine standard clinical testing. The contribution of proprioceptive deficits to the impairment of FA patients might therefore indeed be underestimated today.

Abstract 138: Procollagen I Carboxyterminal Propeptide Levels in Friedreich Ataxia and Its Relation to Subclinical Myocardial Disease

Background: Friedreich ataxia (FA) is the most common recessive hereditary ataxia. Triplet expansion (GAA) of the frataxin gene leads to intramitochondrial iron accumulation, and cardiomyopathy is the leading cause of death in FA. Histopathologic analysis of autopsy hearts has shown myocardial fibrosis and concentric left ventricular (LV) thickening, which our group has previously shown in vivo in FA patients using cardiac magnetic resonance with late gadolinium enhancement (LGE-CMR). Procollagen I carboxyterminal propeptide (PICP) is a serum marker of collagen synthesis, suggesting potential utility as a biomarker of myocardial fibrosis and remodeling. Objectives: The aims of this work were to 1) determine PICP levels in FA patients compared to similar-aged healthy controls, 2) evaluate PICP levels relative to GAA repeat length, 3) evaluate PICP in the context of cardiac remodeling and 4) compare serum PICP levels to presence or absence of fibrosis by LGE-CMR. Methods: 30 FA patients (34.2±11.8 years) underwent measurement of serum PICP using sandwich ELISA as well as CMR examination with cine and LGE acquisitions. Southern blot analysis was performed to measure GAA repeats, recording the minimum of 2 values for each FA patient. 5 healthy volunteers (37.6±8.4 years) served as controls for PICP measurement. Cine images were analyzed at end-diastole to compute relative wall thickness (RWT), a marker of concentric remodeling. Results: PICP values were markedly elevated in FA patients compared to normal controls (1034±76 vs. 657±89 ng/mL, p=0.004). Minimum GAA repeat length was moderately correlated with greater RWT (r=0.40, p=0.041) but did not predict PICP level. Higher PICP level modestly predicted worse concentric remodeling (r=0.39, p=0.033). However, PICP did not distinguish between 15 patients with evident myocardial fibrosis by LGE vs. 15 LGE-negative FA patients (1042±128 vs 1027±87 ng/mL, p=0.925). Conclusions: PICP, a serum marker of collagen synthesis, is significantly elevated in FA patients with higher values indicating adverse LV remodeling. PICP may provide complementary information to direct myocardial fibrosis imaging, and warrants further evaluation as a biomarker of disease severity and treatment response.

Two New Pimelic Diphenylamide HDAC Inhibitors Induce Sustained Frataxin Upregulation in Cells from Friedreich's Ataxia Patients and in a Mouse Model

BackgroundFriedreich's ataxia (FRDA), the most common recessive ataxia in Caucasians, is due to severely reduced levels of frataxin, a highly conserved protein, that result from a large GAA triplet repeat expansion within the first intron of the frataxin gene (FXN). Typical marks of heterochromatin are found near the expanded GAA repeat in FRDA patient cells and mouse models. Histone deacetylase inhibitors (HDACIs) with a pimelic diphenylamide structure and HDAC3 specificity can decondense the chromatin structure at the FXN gene and restore frataxin levels in cells from FRDA patients and in a GAA repeat based FRDA mouse model, KIKI, providing an appealing approach for FRDA therapeutics.Methodology/Principal FindingsIn an effort to further improve the pharmacological profile of pimelic diphenylamide HDACIs as potential therapeutics for FRDA, we synthesized additional compounds with this basic structure and screened them for HDAC3 specificity. We characterized two of these compounds, 136 and 109, in FRDA patients' peripheral blood lymphocytes and in the KIKI mouse model. We tested their ability to upregulate frataxin at a range of concentrations in order to determine a minimal effective dose. We then determined in both systems the duration of effect of these drugs on frataxin mRNA and protein, and on total and local histone acetylation. The effects of these compounds exceeded the time of direct exposure in both systems.Conclusions/SignificanceOur results support the pre-clinical development of a therapeutic approach based on pimelic diphenylamide HDACIs for FRDA and provide information for the design of future human trials of these drugs, suggesting an intermittent administration of the drug.

Limitations in a frataxin knockdown cell model for Friedreich ataxia in a high-throughput drug screen

BackgroundPharmacological high-throughput screening (HTS) represents a powerful strategy for drug discovery in genetic diseases, particularly when the full spectrum of pathological dysfunctions remains unclear, such as in Friedreich ataxia (FRDA). FRDA, the most common recessive ataxia, results from a generalized deficiency of mitochondrial and cytosolic iron-sulfur cluster (ISC) proteins activity, due to a partial loss of frataxin function, a mitochondrial protein proposed to function as an iron-chaperone for ISC biosynthesis. In the absence of measurable catalytic function for frataxin, a cell-based assay is required for HTS assay.MethodsUsing a targeted ribozyme strategy in murine fibroblasts, we have developed a cellular model with strongly reduced levels of frataxin. We have used this model to screen the Prestwick Chemical Library, a collection of one thousand off-patent drugs, for potential molecules for FRDA.ResultsThe frataxin deficient cell lines exhibit a proliferation defect, associated with an ISC enzyme deficit. Using the growth defect as end-point criteria, we screened the Prestwick Chemical Library. However no molecule presented a significant and reproducible effect on the proliferation rate of frataxin deficient cells. Moreover over numerous passages, the antisense ribozyme fibroblast cell lines revealed an increase in frataxin residual level associated with the normalization of ISC enzyme activities. However, the ribozyme cell lines and FRDA patient cells presented an increase in Mthfd2 transcript, a mitochondrial enzyme that was previously shown to be upregulated at very early stages of the pathogenesis in the cardiac mouse model.ConclusionAlthough no active hit has been identified, the present study demonstrates the feasibility of using a cell-based approach to HTS for FRDA. Furthermore, it highlights the difficulty in the development of a stable frataxin-deficient cell model, an essential condition for productive HTS in the future.

Frataxin is essential for extramitochondrial Fe–S cluster proteins in mammalian tissues

Friedreich ataxia, the most common recessive ataxia, is caused by the deficiency of the mitochondrial protein frataxin (Fxn), an iron chaperone involved in the assembly of Fe-S clusters (ISC). In yeast, mitochondria play a central role for all Fe-S proteins, independently of their subcellular localization. In mammalian cells, this central role of mitochondria remains controversial as an independent cytosolic ISC assembly machinery has been suggested. In the present work, we show that three extramitochondrial Fe-S proteins (xanthine oxido-reductase, glutamine phosphoribosylpyrophosphate amidotransferase and Nth1) are affected in Fxn-deleted mouse tissues. Furthermore, we show that Fxn is strictly localized to the mitochondria, excluding the presence of a cytosolic pool of Fxn in normal adult tissues. Together, these results demonstrate that in mammals, Fxn and mitochondria play a cardinal role in the maturation of extramitochondrial Fe-S proteins. The Fe-S scaffold protein IscU progressively decreases in Fxn-deleted tissues, further contributing to the impairment of Fe-S proteins. These results thus provide new cellular pathways that may contribute to molecular mechanisms of the disease.

Infectious Delivery and Expression of a 135 kb Human FRDA Genomic DNA Locus Complements Friedreich's Ataxia Deficiency in Human Cells

Friedreich's ataxia (FA) is the most common recessive ataxia, affecting 1-2 in 50,000 Caucasians, and there is currently no effective cure or treatment. FA results from a deficiency of the mitochondrial protein frataxin brought about by a repeat expansion in intron 1 of the FRDA gene. The main areas affected are the central nervous system (particularly the spinocerebellar system) and cardiac tissue. Therapies aimed at alleviating the neurological degeneration have proved unsuccessful to date. Here, we describe the construction and delivery of high capacity herpes simplex virus type 1 (HSV-1) amplicon vectors expressing the entire 80 kb FRDA genomic locus, driven by the endogenous FRDA promoter and including all introns and flanking regulatory sequences within a 135 kb genomic DNA insert. FA patient primary fibroblasts deficient in frataxin protein and exhibiting sensitivity to oxidative stress were transduced at high efficiency by FRDA genomic locus vectors. Following vector transduction, expression of FRDA protein by immunofluorescence was shown. Finally, functional complementation studies demonstrated restoration of the wild-type cellular phenotype in response to oxidative stress in transduced FA patient cells. These results suggest the potential of the infectious bacterial artificial chromosome-FRDA vectors for gene therapy of FA.

1070. Infectious Delivery and Prolonged Expression of a 135 kb Human Friedreich’s Ataxia Genomic DNA Locus in Human and Mouse Neuronal Cells

Friedreich's ataxia (FA) is the most common recessive ataxia, affecting 1|[ndash]|2 in 50,000 Caucasians, and there is currently no effective cure or treatment. FA results from a deficiency in frataxin, a mitochondrial protein, caused by repeat expansion in intron 1 of the FRDA gene. The main areas affected are the central nervous system (particularly the spinocerebellar system) and the cardiac tissue. Therapies aimed at alleviating the neurological degeneration have proved unsuccessful to date, although some treatments based upon administration of antioxidants have been used to treat the cardiac condition. We are interested in developing a functional complementation gene therapy strategy to treat the neurological disorder and correct mitochondrial dysfunction.

956. HSV-1 Amplicon iBAC-FRDA Genomic Locus Delivery for the Treatment of Friedreich's Ataxia

Friedreich's Ataxia (FA) is the most common recessive ataxia, affecting 1-2 in 50,000 Caucasians. FA is caused by a deficiency in frataxin, a mitochondrial protein encoded by the FRDA gene and involved in iron trafficking-related processes. The main areas affected are the central nervous system (particularly the spinocerebellar system) and cardiac tissue. Although some treatments based upon administration of anti-oxidants have proven to be successful for treating the cardiac condition, therapies aimed at alleviating the neurological degeneration have failed so far.

Friedreich ataxia mouse models with progressive cerebellar and sensory ataxia reveal autophagic neurodegeneration in dorsal root ganglia.

Friedreich ataxia (FRDA), the most common recessive ataxia, is characterized by degeneration of the large sensory neurons of the spinal cord and cardiomyopathy. It is caused by severely reduced levels of frataxin, a mitochondrial protein involved in iron-sulfur cluster (ISC) biosynthesis. Through a spatiotemporally controlled conditional gene-targeting approach, we have generated two mouse models for FRDA that specifically develop progressive mixed cerebellar and sensory ataxia, the most prominent neurological features of FRDA. Histological studies showed both spinal cord and dorsal root ganglia (DRG) anomalies with absence of motor neuropathy, a hallmark of the human disease. In addition, one line revealed a cerebellar granule cell loss, whereas both lines had Purkinje cell arborization defects. These lines represent the first FRDA models with a slowly progressive neurological degeneration. We identified an autophagic process as the causative pathological mechanism in the DRG, leading to removal of mitochondrial debris and apparition of lipofuscin deposits. These mice therefore represent excellent models for FRDA to unravel the pathological cascade and to test compounds that interfere with the degenerative process.