Fragile X Tremor Ataxia Syndrome Research Articles

Ultra-high-field 7-Tesla magnetic resonance imaging in fragile X tremor/ataxia syndrome (FXTAS).

Fragile X tremor/ataxia syndrome (FXTAS) is an adult-onset neurodegenerative disorder characterized by premutation expansion of fragile X mental retardation 1 (FMR1) gene. It is a common single-gene cause of tremor, ataxia, and cognitive decline in adults. FXTAS affects the central, peripheral and autonomic nervous systems, leading to a range of neurological symptoms from dementia to dysautonomia. A characteristic imaging feature of FXTAS is symmetric T2 hyperintensity in the deep white matter of the cerebellar hemispheres and middle cerebral peduncle. However, recent studies have reported additional findings on diffusion weighted images (DWI), such as a symmetric high-intensity band-like signal at the cerebral corticomedullary junction. These findings, along with the characteristic cerebellar signal alterations, overlap with imaging findings seen in adult-onset neuronal intranuclear inclusion disease (NIID). Importantly, recent pathology studies have shown that both FXTAS and NIID can manifest intranuclear inclusion bodies, posing a diagnostic challenge and potential for misdiagnosis. We describe a 58-year-old man with FXTAS who received an erroneous diagnosis based on imaging and histopathology results. We emphasize the potential pitfalls in distinguishing NIID from FXTAS and stress the importance of genetic analysis in all cases with suspected NIID and FXTAS for confirmation. Additionally, we present the 7T MRI brain findings of FXTAS.

448 Establishing the efficacy of naturally occurring endocannabinoid-like substance in an in vitro model of Fragile X Tremor/Ataxia Syndrome (FXT/AS)

OBJECTIVES/GOALS: FXT/AS is a devastating, rare neurological syndrome that negatively impacts movement and cognition and is suspected to induce mitochondria dysfunction. Currently, no effective pharmacological treatments for FXTAS exist. The goal is to restore mitochondrial viability using endocannabinoid-like compounds in a cell culture model of FXTAS. METHODS/STUDY POPULATION: To establish a cell model of mitochondrial dysfunction, fibroblast baby hamster kidney (BHK-21) cell lines were treated with glucose oxidase (GluOx) at varying concentrations and times. Mitochondrial viability was assessed by the colorimetric Janus B Green Assay, which stains the mitochondria and enables assessment of cell numbers and the presence of oxygen in anchorage-dependent cell culture. Upon establishing this model of mitochondrial dysfunction, we next investigated the ability of three novel mitochondrial antioxidants (e.g., macamides) to protect mitochondrial viability. RESULTS/ANTICIPATED RESULTS: GluOx treatment of BHK-21 cells caused a dose- and time-dependent increase in oxidative stress. The data demonstrated significant disruption in the morphology of BHK-21 cells at a high glucose concentration, i.e., 40 nM, between 2 and 24 hours post-exposure. The morphology data were confirmed by the Janus B Green colorimetric assay. In examining the effects of glucose on mitochondrial viability, we demonstrated that at 15, 30, 35, and 40 nM, glucose significantly decreased mitochondria viability compared to the untreated, with 40 nM having the greatest effect. Under these conditions of mitochondrial dysfunction, co-incubation of the cells with the 0.5 uM MAM69 macamide attenuated the GluOx-induced increase in oxidative stress, with 0.5 uM MAM69 alone showing no effect on mitochondria viability. DISCUSSION/SIGNIFICANCE: This study illustrates the efficacy of macamides, natural occurring endocannabinoid like-compound, as novel prognostic and therapeutic candidates in the treatment of mitochondrial dysfunction that is associated with FXTAS. The use of BHK-21 fibroblast cells provides a rapid screening model to test for pharmacological therapeutic efficacy.

EP273: The critical role of NDF2 domain in FMR1 supported by a novel variant in two brothers with intellectual disability

The FMR1 gene encodes for FMRP, a RNA-binding protein implicated in the regulation of mRNA translation and/or transport. An expansion of the trinucleotide repeats (CGG) in the 5' UTR, which is normally found at 6-53 copies, is the cause of fragile X syndrome, premature ovarian failure (POF1), and fragile X tremor/ataxia syndrome (FTXAS) depending on the degree of trinucleotide repeat expansion.

Unusual Presentation of PLA2G6-Related Neurodegeneration with Retinal Vasculitis.

Unusual Presentation of PLA2G6-Related Neurodegeneration with Retinal Vasculitis.

RNA toxicity in non-coding repeat expansion disorders.

Several neurodegenerative disorders like amyotrophic lateral sclerosis (ALS) and spinocerebellar ataxia (SCA) are caused by non‐coding nucleotide repeat expansions. Different pathogenic mechanisms may underlie these non‐coding repeat expansion disorders. While gain‐of‐function mechanisms, such as toxicity associated with expression of repeat RNA or toxicity associated with repeat‐associated non‐ATG (RAN) products, are most frequently connected with these disorders, loss‐of‐function mechanisms have also been implicated. We review the different pathways that have been linked to non‐coding repeat expansion disorders such as C9ORF72‐linked ALS/frontotemporal dementia (FTD), myotonic dystrophy, fragile X tremor/ataxia syndrome (FXTAS), SCA, and Huntington's disease‐like 2. We discuss modes of RNA toxicity focusing on the identity and the interacting partners of the toxic RNA species. Using the C9ORF72 ALS/FTD paradigm, we further explore the efforts and different methods used to disentangle RNA vs. RAN toxicity. Overall, we conclude that there is ample evidence for a role of RNA toxicity in non‐coding repeat expansion diseases.

In Vitro Synthesis and RNA Structure Probing of CUG Triplet Repeat RNA.

Aberrant RNA structure plays a central role in the molecular mechanisms guided by repeat RNAs in diseases like myotonic dystrophy (DM), C9orf72-linked amyotrophic lateral sclerosis (ALS) and fragile X tremor/ataxia syndrome (FXTAS). Much knowledge remains to be gained about how these repeat-expanded transcripts are actually folded, especially regarding the properties specific to very long and interrupted repeats. RNA structure can be interrogated by chemical as well as enzymatic probes. These probes usually bind or cleave single-stranded nucleotides, which can subsequently be detected using reverse transcriptase primer extension. In this chapter, we describe methodology for in vitro synthesis and structure probing of expanded CUG repeat RNAs associated with DM type 1 and approaches for the associated data analysis.

CGG Repeats in the 5'UTR of FMR1 RNA Regulate Translation of Other RNAs Localized in the Same RNA Granules.

CGG repeats in the 5’UTR of Fragile X Mental Retardation 1 (FMR1) RNA mediate RNA localization and translation in granules. Large expansions of CGG repeats (> 200 repeats) in FMR1, referred to as full mutations, are associated with fragile X syndrome (FXS). Smaller expansions (55–200 repeats), referred to as premutations, are associated with fragile X tremor ataxia syndrome (FXTAS) and fragile X premature ovarian insufficiency (FXPOI). TMPyP4 is a porphyrin ring compound that destabilizes CGG repeat RNA secondary structure. Here we show that exogenous CGG repeat RNA by itself, lacking the FMRP ORF, microinjected into hippocampal neurons is localized in RNA granules and inhibits translation of ARC RNA, which is localized in the same granules. TMPyP4 rescues translation of ARC RNA in granules. We also show that in human premutation fibroblasts with endogenous CGG repeat expansions in the FMR1 gene, translation of ARC RNA is inhibited and calcium homeostasis is disrupted and both phenotypes are rescued by TMPyP4. Inhibition of granule translation by expanded CGG repeats and rescue of granule translation by TMPy4, represent potential pathogenic mechanism and therapeutic strategy, respectively, for FXTAS and FXPOI.

The Long Non-Coding RNAs in Neurodegenerative Diseases: Novel Mechanisms of Pathogenesis.

Long-non-coding RNAs (lncRNAs), RNA molecules longer than 200 nucleotides, have been involved in several biological processes and in a growing number of diseases, controlling gene transcription, pre-mRNA processing, the transport of mature mRNAs to specific cellular compartments, the regulation of mRNA stability, protein translation and turnover. The fundamental role of lncRNAs in central nervous system (CNS) is becoming increasingly evident. LncRNAs are abundantly expressed in mammalian CNS in a specific spatio-temporal manner allowing a quick response to environmental/molecular changes. This article reviews the biology and mechanisms of action of lncRNAs underlying their potential role in CNS and in some neurodegenerative diseases. an increasing number of studies report on lncRNAs involvement in different molecular mechanisms of gene expression modulation in CNS, from neural stem cell differentiation mainly by chromatin remodeling, to control of neuronal activities. More recently, lncRNAs have been implicated in neurodegenerative diseases, including Alzheimer's Disease, where the role of BACE1-AS lncRNA has been widely defined. BACE1-AS levels are up-regulated in AD brains where BACE1-AS acts by stabilizing BACE1 mRNA thereby increasing BACE1 protein content and Aβ42 formation. In Frontotemporal dementia and Amyotrophic lateral sclerosis the lncRNAs NEAT1_2 and MALAT1 co-localize at nuclear paraspeckles with TDP-43 and FUS proteins and their binding to TDP-43 is markedly increased in affected brains. In Parkinson's Disease the lncRNA UCHL1-AS1 acts by directly promoting translation of UCHL1 protein leading to perturbation of the ubiquitin-proteasome system. Different lncRNAs, such as HTT-AS, BDNF-AS and HAR1, were found to be dysregulated in their expression also in Huntington's Disease. In Fragile X syndrome (FXS) and Fragile X tremor/ataxia syndrome (FXTAS) patients, the presence of CGG repeats expansion alters the expression of the lncRNAs FMR1-AS1 and FMR6. Interestingly, they are expressed in peripheral blood leukocytes, suggesting these lncRNAs may represent biomarkers for FXS/FXTAS early detection and therapy. Finally, the identification of the antisense RNAs SCAANT1-AS and ATXN8OS in spinocerebellar ataxia 7 and 8, respectively, suggests that very different mechanisms of action driven by lncRNAs may trigger neurodegeneration in these disorders. The emerging role of lncRNAs in neurodegenerative diseases suggests that their dysregulation could trigger neuronal death via still unexplored RNA-based regulatory mechanisms which deserve further investigation. The evaluation of their diagnostic significance and therapeutic potential could also address the setting up of novel treatments in diseases where no cure is available to date.

Fragile X tremor ataxia syndrome and white matter dementia

Objective: Fragile X tremor ataxia syndrome (FXTAS) is an inherited neurodegenerative disease in which dementia is common and disabling. The pathogenesis of dementia in FXTAS is poorly understood, but the salience of executive dysfunction and slowed processing speed, the frequent presence of the middle cerebellar peduncle sign on magnetic resonance imaging (MRI), and striking neuropathological alterations of white matter all suggest that myelinated tracts are significantly involved. This paper considers the role of white matter disease in FXTAS dementia, particularly with regard to the concept of white matter dementia (WMD). Method: A focused review of FXTAS in relation to known white matter disorders is provided to propose that the concept of WMD may illuminate the basis of dementia in FXTAS. The putative pathogenetic contribution of white matter involvement in other neurodegenerative diseases is also considered. Results: Considerable evidence supports the importance of white matter disease in the pathogenesis of dementia in FXTAS. Whereas, gray matter regions are also involved, white matter degeneration is prominent, even early in the disease, and correlates with executive dysfunction and slowed processing speed. Evidence for white matter involvement in other neurodegenerative diseases lends additional support to the relevance of white matter in FXTAS. Conclusion: The dementia of FXTAS is closely related to the profile of WMD, and white matter involvement is also supported by MRI and neuropathological observations. White matter pathology is also relevant to the pathogenesis of other neurodegenerative diseases. Further study of white matter promises to clarify the origin of dementia in FXTAS.

Proteostasis and RNA Binding Proteins in Synaptic Plasticity and in the Pathogenesis of Neuropsychiatric Disorders.

Decades of research have demonstrated that rapid alterations in protein abundance are required for synaptic plasticity, a cellular correlate for learning and memory. Control of protein abundance, known as proteostasis, is achieved across a complex neuronal morphology that includes a tortuous axon as well as an extensive dendritic arbor supporting thousands of individual synaptic compartments. To regulate the spatiotemporal synthesis of proteins, neurons must efficiently coordinate the transport and metabolism of mRNAs. Among multiple levels of regulation, transacting RNA binding proteins (RBPs) control proteostasis by binding to mRNAs and mediating their transport and translation in response to synaptic activity. In addition to synthesis, protein degradation must be carefully balanced for optimal proteostasis, as deviations resulting in excess or insufficient abundance of key synaptic factors produce pathologies. As such, mutations in components of the proteasomal or translational machinery, including RBPs, have been linked to the pathogenesis of neurological disorders such as Fragile X Syndrome (FXS), Fragile X Tremor Ataxia Syndrome (FXTAS), and Autism Spectrum Disorders (ASD). In this review, we summarize recent scientific findings, highlight ongoing questions, and link basic molecular mechanisms to the pathogenesis of common neuropsychiatric disorders.

White matter disease and cognitive impairment in FMR1 premutation carriers.

This cross-sectional, observational study examined the role of white matter involvement in the cognitive impairment of individuals with the fragile X mental retardation 1 (FMR1) premutation. Eight asymptomatic premutation carriers, 5 participants with fragile X tremor/ataxia syndrome (FXTAS), and 7 noncarrier controls were studied. The mean age of the asymptomatic premutation carriers, participants with FXTAS, and noncarrier controls was 60, 71, and 67 years, respectively. Magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) were used to examine the middle cerebellar peduncles (MCP) and the genu and splenium of the corpus callosum in relation to executive function and processing speed. MRS measures were N-acetyl aspartate/creatine (NAA/Cr) and choline/creatine, and fractional anisotropy (FA) was used for DTI. Executive function was assessed with the Behavioral Dyscontrol Scale and the Controlled Oral Word Association Test (COWAT), and processing speed with the Symbol Digit Modalities Test. Among all 13 FMR1 premutation carriers, significant correlations were found between N-acetyl aspartate/creatine and choline/creatine in the MCP and COWAT scores, and between FA in the genu and performance on the Behavioral Dyscontrol Scale, COWAT, and Symbol Digit Modalities Test; a correlation was also found between FA in the splenium and COWAT performance. In all regions studied, participants with FXTAS had the lowest mean FA. Microstructural white matter disease as determined by MRS and DTI correlated with executive dysfunction and slowed processing speed in these FMR1 premutation carriers. Neuroimaging abnormalities in the genu and MCP suggest that disruption of white matter within frontocerebellar networks has an important role in the cognitive impairment associated with the FMR1 premutation.

Associated features in females with an FMR1 premutation.

Changes in the fragile X mental retardation 1 gene (FMR1) have been associated with specific phenotypes, most specifically those of fragile X syndrome (FXS), fragile X tremor/ataxia syndrome (FXTAS), and fragile X primary ovarian insufficiency (FXPOI). Evidence of increased risk for additional medical, psychiatric, and cognitive features and conditions is now known to exist for individuals with a premutation, although some features have been more thoroughly studied than others. This review highlights the literature on medical, reproductive, cognitive, and psychiatric features, primarily in females, that have been suggested to be associated with changes in the FMR1 gene. Based on this review, each feature is evaluated with regard to the strength of evidence of association with the premutation. Areas of need for additional focused research and possible intervention strategies are suggested.

Blood expression profiles of fragile X premutation carriers identify candidate genes involved in neurodegenerative and infertility phenotypes

Male premutation carriers presenting between 55 and 200 CGG repeats in the Fragile-X-associated (FMR1) gene are at risk of developing Fragile X Tremor/Ataxia Syndrome (FXTAS), and females undergo Premature Ovarian Failure (POF1). Here, we have evaluated gene expression profiles from blood in male FMR1 premutation carriers and detected a strong deregulation of genes enriched in FXTAS relevant biological pathways, including inflammation, neuronal homeostasis and viability. Gene expression profiling distinguished between control individuals, carriers with FXTAS and carriers without FXTAS, with levels of expanded FMR1 mRNA being increased in FXTAS patients. In vitro studies in a neuronal cell model indicate that expression levels of expanded FMR1 5′-UTR are relevant in modulating the transcriptome. Thus, perturbations of the transcriptome may be an interplay between the CGG expansion size and FMR1 expression levels. Several deregulated genes (DFFA, BCL2L11, BCL2L1, APP, SOD1, RNF10, HDAC5, KCNC3, ATXN7, ATXN3 and EAP1) were validated in brain samples of a FXTAS mouse model. Downregulation of EAP1, a gene involved in the female reproductive system physiology, was confirmed in female carriers. Decreased levels were detected in female carriers with POF1 compared to those without POF1, suggesting that EAP1 levels contribute to ovarian insufficiency. In summary, gene expression profiling in blood has uncovered mechanisms that may underlie different pathological aspects of the premutation. A better understanding of the transcriptome dynamics in relation with expanded FMR1 mRNA expression levels and CGG expansion size may provide mechanistic insights into the disease process and a more accurate FXTAS diagnosis to the myriad of phenotypes associated with the premutation.

Repeat-associated non-ATG (RAN) translation in neurological disease

Well-established rules of translational initiation have been used as a cornerstone in molecular biology to understand gene expression and to frame fundamental questions on what proteins a cell synthesizes, how proteins work and to predict the consequences of mutations. For a group of neurological diseases caused by the abnormal expansion of short segments of DNA (e.g. CAG•CTG repeats), mutations within or outside of predicted coding and non-coding regions are thought to cause disease by protein gain- or loss-of-function or RNA gain-of-function mechanisms. In contrast to these predictions, the recent discovery of repeat-associated non-ATG (RAN) translation showed expansion mutations can express homopolymeric expansion proteins in all three reading frames without an AUG start codon. This unanticipated, non-canonical type of protein translation is length-and hairpin-dependent, takes place without frameshifting or RNA editing and occurs across a variety of repeat motifs. To date, RAN proteins have been reported in spinocerebellar ataxia type 8 (SCA8), myotonic dystrophy type 1 (DM1), fragile X tremor ataxia syndrome (FXTAS) and C9ORF72 amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD). In this article, we review what is currently known about RAN translation and recent progress toward understanding its contribution to disease.

Ages of Onset of Mood and Anxiety Disorders in Fragile X Premutation Carriers

Objective: FMR1 premutation carriers of both genders have a high lifetime prevalence of anxiety and depressive disorders, however little is known regarding the onset ages of these conditions. This study compared onset ages of mood and anxiety disorders in premutation carriers with typical onset ages of the same disorders in the general population. Methods: Eighty-one premutation carriers (42% men; average age 62, SD 10) with and without FXTAS completed the Structured Clinical Interview for DSM-IV-TR. Onset ages of mood and anxiety disorders were compared to the corresponding typical population onset ages using the signed rank test. Results: Overall median onset ages of MDD (46 years old, p < 0.0001), panic disorder (40 years old, p = 0.0067), and specific phobia (11.5 years old, p = 0.0003) were significantly higher in premutation carriers compared to the general population. Median MDD onset ages in male carriers (52 years old) and those with FXTAS (49.5 years old) were significantly higher relative to the general population (median 32, both p < 0.0001). Tremor and ataxia emerged significantly later than MDD and the anxiety disorders studied. Conclusion: Depressive and anxiety disorders in premutation carriers have a later onset compared to the general population, but precede the onset of motor symptoms. This may be due to progressive mRNA toxicity in the limbic system, white matter changes leading to neuronal dysconnectivity, and interaction with environmental factors. Psychosocial factors may be protective. Further research is needed to understand the full spectrum of psychiatric phenotypes in FMR1 premutation carriers. Keywords: FMR1 premutation, Fragile X tremor/ataxia syndrome (FXTAS), Onset age, MDD, Depression, Anxiety

Ovarian histopathological and ubiquitin‐immunophenotypic features in fragile X‐associated primary ovarian insufficiency: a study of five cases and selected controls

Sir: The fragile X premutation, an expansion of a CGG triplet repeat in the 5′-untranslated region of the FMR1 gene (55–200 repeats), is one of the most common aetiologies of primary ovarian insufficiency: fragile X-associated primary ovarian insufficiency (FXPOI).1–3 Men who carry the premutation are at increased risk for a late-onset neurodegenerative disorder termed fragile X tremor/ataxia syndrome (FXTAS).4 In premutation carriers, FMR1 is transcribed at increased levels, and the large rCGG tracks may cause disease by acting in a toxic gain of function manner.5–8

Histone Deacetylases Suppress CGG Repeat–Induced Neurodegeneration Via Transcriptional Silencing in Models of Fragile X Tremor Ataxia Syndrome

Fragile X Tremor Ataxia Syndrome (FXTAS) is a common inherited neurodegenerative disorder caused by expansion of a CGG trinucleotide repeat in the 5′UTR of the fragile X syndrome (FXS) gene, FMR1. The expanded CGG repeat is thought to induce toxicity as RNA, and in FXTAS patients mRNA levels for FMR1 are markedly increased. Despite the critical role of FMR1 mRNA in disease pathogenesis, the basis for the increase in FMR1 mRNA expression is unknown. Here we show that overexpressing any of three histone deacetylases (HDACs 3, 6, or 11) suppresses CGG repeat–induced neurodegeneration in a Drosophila model of FXTAS. This suppression results from selective transcriptional repression of the CGG repeat–containing transgene. These findings led us to evaluate the acetylation state of histones at the human FMR1 locus. In patient-derived lymphoblasts and fibroblasts, we determined by chromatin immunoprecipitation that there is increased acetylation of histones at the FMR1 locus in pre-mutation carriers compared to control or FXS derived cell lines. These epigenetic changes correlate with elevated FMR1 mRNA expression in pre-mutation cell lines. Consistent with this finding, histone acetyltransferase (HAT) inhibitors repress FMR1 mRNA expression to control levels in pre-mutation carrier cell lines and extend lifespan in CGG repeat–expressing Drosophila. These findings support a disease model whereby the CGG repeat expansion in FXTAS promotes chromatin remodeling in cis, which in turn increases expression of the toxic FMR1 mRNA. Moreover, these results provide proof of principle that HAT inhibitors or HDAC activators might be used to selectively repress transcription at the FMR1 locus.

Mapping self-reports of working memory deficits to executive dysfunction in Fragile X Mental Retardation 1 ( FMR1) gene premutation carriers asymptomatic for FXTAS

Fragile X Syndrome is a neurodevelopmental disorder that is caused by the silencing of a single gene on the X chromosome, the Fragile X Mental Retardation 1 ( FMR1) gene. In recent years, the premutation (“carrier”) status has received considerable attention and there is now an emerging consensus that despite intellectual functioning being within the average range premutation males present with subtle executive function impairments that include poor inhibitory control, working memory deficits, and poor planning skills. The ranges of these skills, although not nearly as severe as seen in the full mutation, nonetheless serve to differentiate males with the premutation from males in the unaffected population. In the present study we extend these findings to suggest that behavioral markers, specifically self-report on the Brown Attention-Deficit Disorder Rating Scales, may serve as a clinically useful indicator or “signature” of the Fragile X Premutation status. We discuss the possibility that this measure provides a means to identify those at greatest risk for developing the newly identified neurodegenerative disorder that affects some premutation males – Fragile X Tremor/Ataxia Syndrome (FXTAS).

Peripheral nervous system pathology in fragile X tremor/ataxia syndrome (FXTAS)

Fragile X tremor/ataxia syndrome (FXTAS) occurs in individuals with moderate CGG expansion of the fragile X mental retardation 1 (FMR1) gene and is associated with intranuclear inclusions in neurons and astrocytes. Although the neuropathologic findings in the brain and spinal cord were described, pathological features in the peripheral nervous system were not reported. Here, we report on novel neuropathological findings in the peripheral nervous system and especially in autonomic ganglia at autopsy in a man with FXTAS. In addition to the characteristic brain and spinal cord findings, typical intranuclear inclusions were identified in the ganglion cells of adrenal medulla, dorsal root ganglia, paraspinal sympathetic ganglia, myenteric ganglia of the stomach and subepicardial autonomic ganglion of the heart. Our findings indicate that FXTAS diffusely involves the central and peripheral nervous systems, which explains the protean neurological symptoms ranging from dementia to dysautonomia.

Symptomatic Treatment of Ataxia

The cupboard is bare when it comes to the symptomatic treatment of ataxia. These authors report apparent success with varenicline, initially given for smoking cessation to a 64-year-old man with prominent ataxia due to fragile X tremor/ataxia syndrome (FXTAS), a 9-year history of tremor, and a 4-year history of gait ataxia with falling. After taking 1 mg of varenicline twice daily for 1 week, he noted a striking …