Fragile X premutation tremor/ataxia syndrome: molecular, clinical, and neuroimaging correlates

The Frequency of Intermediate Alleles in Patients with Cerebellar Phenotypes

Cerebellar syndromes are clinically and etiologically heterogeneous and can be classified as hereditary, neurodegenerative non-hereditary, or acquired. Few data are available on the frequency of each form in the clinical setting. Growing interest is emerging regarding the genetic forms caused by triplet repeat expansions. Alleles with repeat expansion lower than the pathological threshold, termed intermediate alleles (IAs), have been found to be associated with disease manifestation. In order to assess the relevance of IAs as a cause of cerebellar syndromes, we enrolled 66 unrelated Italian ataxic patients and described the distribution of the different etiology of their syndromes and the frequency of IAs. Each patient underwent complete clinical, hematological, and neurophysiological assessments, neuroimaging evaluations, and genetic tests for autosomal dominant cerebellar ataxia (SCA) and fragile X-associated tremor/ataxia syndrome (FXTAS). We identified the following diagnostic categories: 28% sporadic adult-onset ataxia, 18% cerebellar variant of multiple system atrophy, 9% acquired forms, 9% genetic forms with full-range expansion, and 12% cases with intermediate-range expansion. The IAs were six in the FMR1 gene, two in the gene responsible for SCA8, and one in the ATXN2 gene. The clinical phenotype of patients carrying the IAs resembles, in most of the cases, the one associated with full-range expansion. Our study provides an exhaustive description of the causes of cerebellar ataxia, estimating for the first time the frequency of IAs in SCAs- and FXTAS-associated genes. The high percentage of cases with IAs supports further screening among patients with cerebellar syndromes.

Advances on the Mechanisms and Therapeutic Strategies in Non-coding CGG Repeat Expansion Diseases

Non-coding CGG repeat expansions within the 5' untranslated region are implicated in a range of neurological disorders, including fragile X-associated tremor/ataxia syndrome, oculopharyngeal myopathy with leukodystrophy, and oculopharyngodistal myopathy. This review outlined the general characteristics of diseases associated with non-coding CGG repeat expansions, detailing their clinical manifestations and neuroimaging patterns, which often overlap and indicate shared pathophysiological traits. We summarized the underlying molecular mechanisms of these disorders, providing new insights into the roles that DNA, RNA, and toxic proteins play. Understanding these mechanisms is crucial for the development of targeted therapeutic strategies. These strategies include a range of approaches, such as antisense oligonucleotides, RNA interference, genomic DNA editing, small molecule interventions, and other treatments aimed at correcting the dysregulated processes inherent in these disorders. A deeper understanding of the shared mechanisms among non-coding CGG repeat expansion disorders may hold the potential to catalyze the development of innovative therapies, ultimately offering relief to individuals grappling with these debilitating neurological conditions.

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.

Potential Prodromal Digital Postural Sway Markers for Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS) Detected via Dual-Tasking and Sensory Manipulation

FXTAS is a neurodegenerative disorder occurring in some Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene premutation carriers (PMCs) and is characterized by cerebellar ataxia, tremor, and cognitive deficits that negatively impact balance and gait and increase fall risk. Dual-tasking (DT) cognitive-motor paradigms and challenging balance conditions may have the capacity to reveal markers of FXTAS onset. Our objectives were to determine the impact of dual-tasking and sensory and stance manipulation on balance in FXTAS and potentially detect subtle postural sway deficits in FMR1 PMCs who are asymptomatic for signs of FXTAS on clinical exam. Participants with FXTAS, PMCs without FXTAS, and controls underwent balance testing using an inertial sensor system. Stance, vision, surface stability, and cognitive demand were manipulated in 30 s trials. FXTAS participants had significantly greater total sway area, jerk, and RMS sway than controls under almost all balance conditions but were most impaired in those requiring vestibular control. PMCs without FXTAS had significantly greater RMS sway compared with controls in the feet apart, firm, single task conditions both with eyes open and closed (EC) and the feet together, firm, EC, DT condition. Postural sway deficits in the RMS postural sway variability domain in asymptomatic PMCs might represent prodromal signs of FXTAS. This information may be useful in providing sensitive biomarkers of FXTAS onset and as quantitative balance measures in future interventional trials and longitudinal natural history studies.

A Review of Brain and Pituitary Gland MRI Findings in Patients with Ataxia and Hypogonadism

The association of cerebellar ataxia and hypogonadism occurs in a heterogeneous group of disorders, caused by different genetic mutations often associated with a recessive inheritance. In these patients, magnetic resonance imaging (MRI) plays a pivotal role in the diagnostic workflow, with a variable involvement of the cerebellar cortex, alone or in combination with other brain structures. Neuroimaging involvement of the pituitary gland is also variable. Here, we provide an overview of the main clinical and conventional brain and pituitary gland MRI imaging findings of the most common genetic mutations associated with the clinical phenotype of ataxia and hypogonadism, with the aim of helping neuroradiologists in the identification of these disorders.

Hereditary Ataxias: From Bench to Clinic, Where Do We Stand?

Cerebellar ataxias are a wide heterogeneous group of movement disorders. Within this broad umbrella of diseases, there are both genetics and sporadic forms. The clinical presentation of these conditions can exhibit a diverse range of symptoms across different age groups, spanning from pure cerebellar manifestations to sensory ataxia and multisystemic diseases. Over the last few decades, advancements in our understanding of genetics and molecular pathophysiology related to both dominant and recessive ataxias have propelled the field forward, paving the way for innovative therapeutic strategies aimed at preventing and arresting the progression of these diseases. Nevertheless, the rarity of certain forms of ataxia continues to pose challenges, leading to limited insights into the etiology of the disease and the identification of target pathways. Additionally, the lack of suitable models hampers efforts to comprehensively understand the molecular foundations of disease's pathophysiology and test novel therapeutic interventions. In the following review, we describe the epidemiology, symptomatology, and pathological progression of hereditary ataxia, including both the prevalent and less common forms of these diseases. Furthermore, we illustrate the diverse molecular pathways and therapeutic approaches currently undergoing investigation in both pre-clinical studies and clinical trials. Finally, we address the existing and anticipated challenges within this field, encompassing both basic research and clinical endeavors.

Case Series: Vestibular Migraines in Fragile X Premutation Carriers

BACKGROUND

Vestibular migraine (VM) is one of the most common causes of recurrent vertigo and presents with a history of spontaneous or positional vertigo with a history of migraine headaches. While research has identified a high prevalence of migraine headaches and vestibular deficits among fragile X premutation carriers, there has been no discussion about VM within this population.

OBJECTIVE

This case series and review seeks to describe the clinical characteristics and pathophysiology of VM among individuals with the fragile X premutation. We also seek to discuss treatment and future steps in addressing VM in this population.

METHODS

A review of the literature regarding vestibular migraine and presentation of migraine headaches and vestibular deficits among premutation carriers was performed. A detailed clinical history of migraine headaches and vertigo was obtained from three patients with the fragile X premutation seen by the senior author (RJH).

RESULTS

All three cases first developed symptoms of migraine headaches earlier in life, with the development of VM near menopause. Two of the three cases developed progressive balance issues following the development of VM. All three cases found that their VM episodes were improved or resolved with pharmacological and/or lifestyle interventions.

CONCLUSIONS

It is important to recognize VM among premutation carriers because beneficial treatments are available. Future studies are needed regarding the prevalence of VM and the relationship to subsequent FXTAS. The pathophysiology of VM remains uncertain but possibilities include mitochondrial abnormalities, cranial nerve VIII toxicity secondary to neurotoxic protein accumulation, and calcitonin gene-related peptide (CGRP) signaling dysfunction due to altered levels of fragile X messenger ribonucleoprotein (FMRP).

PGT-M for Premature Ovarian Failure Related to CGG Repeat Expansion of the FMR1 Gene

Primary ovarian failure (POF) is caused by follicle exhaustion and is associated with menstrual irregularities and elevated gonadotropin levels, which lead to infertility before the age of 40 years. The etiology of POI is mostly unknown, but a heterogeneous genetic and familial background can be identified in a subset of cases. Abnormalities in the fragile X mental retardation 1 gene (FMR1) are among the most prevalent monogenic causes of POI. These abnormalities are caused by the expansion of an unstable CGG repeat in the 5' untranslated region of FMR1. Expansions over 200 repeats cause fragile X syndrome (FXS), whereas expansions between 55 and 200 CGG repeats, which are defined as a fragile X premutation, have been associated with premature ovarian failure type 1 (POF1) in heterozygous females. Preimplantation genetic testing for monogenic diseases (PGT-M) can be proposed when the female carries a premutation or a full mutation. In this narrative review, we aim to recapitulate the clinical and molecular features of POF1 and their implications in the context of PGT-M.

Advances in the discovery and analyses of human tandem repeats

Long-read sequencing platforms provide unparalleled access to the structure and composition of all classes of tandemly repeated DNA from STRs to satellite arrays. This review summarizes our current understanding of their organization within the human genome, their importance with respect to disease, as well as the advances and challenges in understanding their genetic diversity and functional effects. Novel computational methods are being developed to visualize and associate these complex patterns of human variation with disease, expression, and epigenetic differences. We predict accurate characterization of this repeat-rich form of human variation will become increasingly relevant to both basic and clinical human genetics.

Open-Label Sulforaphane Trial in FMR1 Premutation Carriers with Fragile-X-Associated Tremor and Ataxia Syndrome (FXTAS)

Fragile X (FMR1) premutation is a common mutation that affects about 1 in 200 females and 1 in 450 males and can lead to the development of fragile-X-associated tremor/ataxia syndrome (FXTAS). Although there is no targeted, proven treatment for FXTAS, research suggests that sulforaphane, an antioxidant present in cruciferous vegetables, can enhance mitochondrial function and maintain redox balance in the dermal fibroblasts of individuals with FXTAS, potentially leading to improved cognitive function. In a 24-week open-label trial involving 15 adults aged 60-88 with FXTAS, 11 participants successfully completed the study, demonstrating the safety and tolerability of sulforaphane. Clinical outcomes and biomarkers were measured to elucidate the effects of sulforaphane. While there were nominal improvements in multiple clinical measures, they were not significantly different after correction for multiple comparisons. PBMC energetic measures showed that the level of citrate synthase was higher after sulforaphane treatment, resulting in lower ATP production. The ratio of complex I to complex II showed positive correlations with the MoCA and BDS scores. Several mitochondrial biomarkers showed increased activity and quantity and were correlated with clinical improvements.

Sensorimotor and inhibitory control in aging FMR1 premutation carriers

Aging FMR1 premutation carriers are at risk of developing neurodegenerative disorders, including fragile X-associated tremor/ataxia syndrome (FXTAS), and there is a need to identify biomarkers that can aid in identification and treatment of these disorders. While FXTAS is more common in males than females, females can develop the disease, and some evidence suggests that patterns of impairment may differ across sexes. Few studies include females with symptoms of FXTAS, and as a result, little information is available on key phenotypes for tracking disease risk and progression in female premutation carriers. Our aim was to examine quantitative motor and cognitive traits in aging premutation carriers. We administered oculomotor tests of visually guided/reactive saccades (motor) and antisaccades (cognitive control) in 22 premutation carriers (73% female) and 32 age- and sex-matched healthy controls. Neither reactive saccade latency nor accuracy differed between groups. FMR1 premutation carriers showed increased antisaccade latencies relative to controls, both when considering males and females together and when analyzing females separately. Reduced saccade accuracy and increased antisaccade latency each were associated with more severe clinically rated neuromotor impairments. Findings indicate that together male and female premutation carriers show a reduced ability to rapidly exert volitional control over prepotent responses and that quantitative differences in oculomotor behavior, including control of visually guided and antisaccades, may track with FXTAS - related degeneration in male and female premutation carriers.

Exploration of SUMO2/3 Expression Levels and Autophagy Process in Fragile X-Associated Tremor/Ataxia Syndrome: Addressing Study Limitations and Insights for Future Research

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that appears in adult FMR1 premutation carriers. The neuropathological hallmark of FXTAS is an intranuclear inclusion in neurons and astrocytes. Nearly 200 different proteins have been identified in FXTAS inclusions, being the small ubiquitin-related modifier 2 (SUMO2), ubiquitin and p62 the most highly abundant. These proteins are components of the protein degradation machinery. This study aimed to characterize SUMO2/3 expression levels and autophagy process in human postmortem brain samples and skin fibroblast cultures from FXTAS patients. Results revealed that FXTAS postmortem brain samples are positive for SUMO2/3 conjugates and supported the idea that SUMO2/3 accumulation is involved in inclusion formation. Insights from RNA-sequencing data indicated that SUMOylation processes are significantly upregulated in FXTAS samples. In addition, the analysis of the autophagy flux showed the accumulation of p62 protein levels and autophagosomes in skin fibroblasts from FXTAS patients. Similarly, gene set analysis evidenced a significant downregulation in gene ontology terms related to autophagy in FXTAS samples. Overall, this study provides new evidence supporting the role of SUMOylation and autophagic processes in the pathogenic mechanisms underlying FXTAS.

Insight and Recommendations for Fragile X-Premutation-Associated Conditions from the Fifth International Conference on FMR1 Premutation

The premutation of the fragile X messenger ribonucleoprotein 1 (FMR1) gene is characterized by an expansion of the CGG trinucleotide repeats (55 to 200 CGGs) in the 5' untranslated region and increased levels of FMR1 mRNA. Molecular mechanisms leading to fragile X-premutation-associated conditions (FXPAC) include cotranscriptional R-loop formations, FMR1 mRNA toxicity through both RNA gelation into nuclear foci and sequestration of various CGG-repeat-binding proteins, and the repeat-associated non-AUG (RAN)-initiated translation of potentially toxic proteins. Such molecular mechanisms contribute to subsequent consequences, including mitochondrial dysfunction and neuronal death. Clinically, premutation carriers may exhibit a wide range of symptoms and phenotypes. Any of the problems associated with the premutation can appropriately be called FXPAC. Fragile X-associated tremor/ataxia syndrome (FXTAS), fragile X-associated primary ovarian insufficiency (FXPOI), and fragile X-associated neuropsychiatric disorders (FXAND) can fall under FXPAC. Understanding the molecular and clinical aspects of the premutation of the FMR1 gene is crucial for the accurate diagnosis, genetic counseling, and appropriate management of affected individuals and families. This paper summarizes all the known problems associated with the premutation and documents the presentations and discussions that occurred at the International Premutation Conference, which took place in New Zealand in 2023.

Dissecting the roles of EIF4G homologs reveals DAP5 as a modifier of CGG repeat-associated toxicity in a Drosophila model of FXTAS

Neurodegeneration in Fragile X-associated tremor/ataxia syndrome (FXTAS) is caused by a CGG trinucleotide repeat expansion in the 5' UTR of FMR1. Expanded CGG repeat RNAs form stable secondary structures, which in turn support repeat-associated non-AUG (RAN) translation to produce toxic peptides. The parameters that impact RAN translation initiation efficiency are not well understood. Here we used a Drosophila melanogaster model of FXTAS to evaluate the role of the eIF4G family of eukaryotic translation initiation factors (EIF4G1, EIF4GII and EIF4G2/DAP5) in modulating RAN translation and CGG repeat-associated toxicity. DAP5 knockdown robustly suppressed CGG repeat-associated toxicity and inhibited RAN translation. Furthermore, knockdown of initiation factors that preferentially associate with DAP5 (such as EIF2β, EIF3F and EIF3G) also selectively suppressed CGG repeat-induced eye degeneration. In mammalian cellular reporter assays, DAP5 knockdown exhibited modest and cell-type specific effects on RAN translation. Taken together, these data support a role for DAP5 in CGG repeat associated toxicity possibly through modulation of RAN translation.

Adult-onset leukodystrophies: a practical guide, recent treatment updates, and future directions

Adult-onset leukodystrophies though individually rare are not uncommon. This group includes several disorders with isolated adult presentations, as well as several childhood leukodystrophies with attenuated phenotypes that present at a later age. Misdiagnoses often occur due to the clinical and radiological overlap with common acquired disorders such as infectious, immune, inflammatory, vascular, metabolic, and toxic etiologies. Increased prevalence of non-specific white matter changes in adult population poses challenges during diagnostic considerations. Clinico-radiological spectrum and molecular landscape of adult-onset leukodystrophies have not been completely elucidated at this time. Diagnostic approach is less well-standardized when compared to the childhood counterpart. Absence of family history and reduced penetrance in certain disorders frequently create a dilemma. Comprehensive evaluation and molecular confirmation when available helps in prognostication, early initiation of treatment in certain disorders, enrollment in clinical trials, and provides valuable information for the family for reproductive counseling. In this review article, we aimed to formulate an approach to adult-onset leukodystrophies that will be useful in routine practice, discuss common adult-onset leukodystrophies with usual and unusual presentations, neuroimaging findings, recent advances in treatment, acquired mimics, and provide an algorithm for comprehensive clinical, radiological, and genetic evaluation that will facilitate early diagnosis and consider active treatment options when available. A high index of suspicion, awareness of the clinico-radiological presentations, and comprehensive genetic evaluation are paramount because treatment options are available for several disorders when diagnosed early in the disease course.

Glial dysregulation in the human brain in fragile X-associated tremor/ataxia syndrome

Short trinucleotide expansions at the FMR1 locus are associated with the late-onset condition fragile X-associated tremor/ataxia syndrome (FXTAS), which shows very different clinical and pathological features from fragile X syndrome (associated with longer expansions), with no clear molecular explanation for these marked differences. One prevailing theory posits that the shorter, premutation expansion uniquely causes extreme neurotoxic increases in FMR1 mRNA (i.e., four to eightfold increases), but evidence to support this hypothesis is largely derived from analysis of peripheral blood. We applied single-nucleus RNA sequencing to postmortem frontal cortex and cerebellum from 7 individuals with premutation and matched controls (n = 6) to assess cell type-specific molecular neuropathology. We found only modest upregulation (~1.3-fold) of FMR1 in some glial populations associated with premutation expansions. In premutation cases, we also identified decreased astrocyte proportions in the cortex. Differential expression and gene ontology analysis demonstrated altered neuroregulatory roles of glia. Using network analyses, we identified cell type-specific and region-specific patterns of FMR1 protein target gene dysregulation unique to premutation cases, with notable network dysregulation in the cortical oligodendrocyte lineage. We used pseudotime trajectory analysis to determine how oligodendrocyte development was altered and identified differences in early gene expression in oligodendrocyte trajectories in premutation cases specifically, implicating early cortical glial developmental perturbations. These findings challenge dogma regarding extremely elevated FMR1 increases in FXTAS and implicate glial dysregulation as a critical facet of premutation pathophysiology, representing potential unique therapeutic targets directly derived from the human condition.

Clinical implications of somatic allele expansion in female FMR1 premutation carriers

Carriers of a premutation allele (PM) in the FMR1 gene are at risk of developing a number of Fragile X premutation asssociated disorders (FXPAC), including Fragile X-associated Tremor/Ataxia Syndrome (FXTAS), Fragile X-associated Primary Ovarian Insufficiency (FXPOI), and Fragile X-associated neuropsychiatric disorders (FXAND). We have recently reported somatic CGG allele expansion in female PM; however, its clinical significance remains unclear. The aim of this study was to examine the potential clinical association between somatic FMR1 allele instability and PM associated disorders. Participants comprised of 424 female PM carriers age 0.3- 90 years. FMR1 molecular measures and clinical information on the presence of medical conditions, were determined for all subjects for primary analysis. Two sub-groups of participants (age ≥ 25, N = 377 and age ≥ 50, N = 134) were used in the analysis related to presence of FXPOI and FXTAS, respectively. Among all participants (N = 424), the degree of instability (expansion) was significantly higher (median 2.5 vs 2.0, P = 0.026) in participants with a diagnosis of attention deficit hyperactivity disorder (ADHD) compared to those without. FMR1 mRNA expression was significantly higher in subjects with any psychiatric disorder diagnosis (P = 0.0017); specifically, in those with ADHD (P = 0.009), and with depression (P = 0.025). Somatic FMR1 expansion was associated with the presence of ADHD in female PM and FMR1 mRNA levels were associated with the presence of mental health disorders. The findings of our research are innovative as they suggest a potential role of the CGG expansion in the clinical phenotype of PM and may potentially guide clinical prognosis and management.

Native functions of short tandem repeats

Over a third of the human genome is comprised of repetitive sequences, including more than a million short tandem repeats (STRs). While studies of the pathologic consequences of repeat expansions that cause syndromic human diseases are extensive, the potential native functions of STRs are often ignored. Here, we summarize a growing body of research into the normal biological functions for repetitive elements across the genome, with a particular focus on the roles of STRs in regulating gene expression. We propose reconceptualizing the pathogenic consequences of repeat expansions as aberrancies in normal gene regulation. From this altered viewpoint, we predict that future work will reveal broader roles for STRs in neuronal function and as risk alleles for more common human neurological diseases.

Fragile X-Associated Neuropsychiatric Disorders (FXAND) in Young Fragile X Premutation Carriers

Background: The fragile X premutation carrier state (PM) (55-200 CGG repeats in the fragile X messenger ribonucleoprotein 1, FMR1 gene) is associated with several conditions, including fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor ataxia (FXTAS), with current literature largely primarily investigating older PM individuals. The aim of this study was to identify the prevalence of fragile X-associated neurodevelopmental disorders (FXAND) in a sample of young PM individuals. Methods: This was a retrospective study conducted through a medical record review of PM individuals who were seen either for clinical concerns (probands, 45.9%) or identified through the cascade testing (non-probands, 54.1%) of an affected sibling with fragile X syndrome. Information on the presence of autism spectrum disorder, attention deficit hyperactivity disorder, anxiety, depression, long-term psychiatric medication intake, and cognitive function, based on standardized assessments, was obtained. Molecular data, including CGG repeat number and FMR1 mRNA levels, were also available for a subset of participants. Analysis included descriptive statistics and a test of comparison to describe the clinical profile of PM individuals pertinent to FXAND. Results: Participants included 61 individuals (52 males and 9 females) aged 7.8 to 20.0 years (mean 12.6 ± 3.4) with a mean full-scale IQ of 90.9 ± 22.7. The majority (N = 52; 85.2%) had at least one mental health disorder, with anxiety being the most common (82.0% of subjects), followed by ADHD (66.5%), and ASD (32.8%). Twenty-seven (87.1%) of non-probands also had at least one mental health condition, with probands having lower cognitive and adaptive skills than non-probands. ASD was present in 20 participants (17/52 males and 3/9 females; 15 probands) with significantly lower FSIQ in those with ASD (mean 73.5 vs. 98.0, p < 0.001). Participants with ASD had a higher number of long-term medications compared to those without (2.32 vs. 1.3, p = 0.002). Conclusions: Our findings indicate a high rate of FXAND diagnoses within a cohort of young PM individuals, including those identified via cascade testing, although this was not a population sample. An awareness of the entity of FXAND and the early recognition of the symptoms of associated conditions may facilitate timely and appropriate care for PM individuals.

Imaging findings and pathological correlations of subacute encephalopathy with neuronal intranuclear inclusion disease–Case report

Neuronal intranuclear inclusion disease (NIID) is a slowly progressive neurodegenerative disease and may sometimes present with symptoms of subacute encephalopathy, including fever, headache, vomiting, and loss of consciousness. We present a case of adult-onset NIID with subacute encephalopathy, which is confirmed by skin and brain biopsied. The magnetic resonance imaging findings show cortical swelling and hyperintensities in the right temporooccipital lobes on T2-weighted images and magnetic resonance angiography demonstrates vasodilatations of the right middle cerebral artery and posterior cerebral artery. Abnormal enhancement is mainly observed in the gyral crowns (crown enhancement). Pathological examinations reveal new infarcts in the deep layers of the cortices. NIID should be considered in the presence of subacute encephalopathy with cortical swelling, contrast enhancement in the temporooccipital lobes, and vasodilation in adult patients. The encephalopathy targeted on the cortices, and the pathological background included infarctions.

CAPRIN1P512L causes aberrant protein aggregation and associates with early-onset ataxia

CAPRIN1 is a ubiquitously expressed protein, abundant in the brain, where it regulates the transport and translation of mRNAs of genes involved in synaptic plasticity. Here we describe two unrelated children, who developed early-onset ataxia, dysarthria, cognitive decline and muscle weakness. Trio exome sequencing unraveled the identical de novo c.1535C > T (p.Pro512Leu) missense variant in CAPRIN1, affecting a highly conserved residue. In silico analyses predict an increased aggregation propensity of the mutated protein. Indeed, overexpressed CAPRIN1^P512L forms insoluble ubiquitinated aggregates, sequestrating proteins associated with neurodegenerative disorders (ATXN2, GEMIN5, SNRNP200 and SNCA). Moreover, the CAPRIN1^P512L mutation in isogenic iPSC-derived cortical neurons causes reduced neuronal activity and altered stress granule dynamics. Furthermore, nano-differential scanning fluorimetry reveals that CAPRIN1^P512L aggregation is strongly enhanced by RNA in vitro. These findings associate the gain-of-function Pro512Leu mutation to early-onset ataxia and neurodegeneration, unveiling a critical residue of CAPRIN1 and a key role of RNA–protein interactions.

Fragile X-associated tremor ataxia syndrome rating scale: Revision and content validity using a mixed method approach

Background

The original Fragile X-associated Tremor Ataxia Syndrome Rating Scale (FXTAS-RS) contained 61 items, some requiring modifications to better meet recommendations for patient-focused rating scale development.

Purpose

Provide initial validation of a revised version of the FXTAS-RS for motor signs.

Method

We conducted a two-phase mixed-method approach. In Phase 1, revision, we implemented a Delphi technique identifying pertinent domains/subdomains and developing items through expert consensus. In Phase 2, content validation, we conducted cognitive pretesting assessing comprehensibility, comprehensiveness, and relevance of items to FXTAS motor signs.

Results

After five rounds of Delphi panel and two rounds of cognitive pretesting, the revised version of the FXTAS-RS was established with 18 items covering five domains and 13 subdomains of motor signs. Cognitive pretesting revealed adequate content validity for the assessment of FXTAS motor signs.

Conclusion

The revised FXTAS-RS has been successfully validated for content and it is now ready for large-scale field validation.

Autism spectrum disorder in the fragile X premutation state: possible mechanisms and implications

There is increasing recognition of the heterogeneity of origin of cases of autism spectrum disorder (ASD) with multiple forms of ASD having been identified over the decades. Among these, a genetic etiology can be identified in 20-40% of cases when a full genetic work-up is completed. The Fragile X premutation state (characterized by the presence of 55-200 CGG repeats in the FMR1 gene) is a relatively newly identified disease state that has since been associated with several disorders including fragile X-associated tremor ataxia syndrome (FXTAS), fragile X-associated primary ovarian insufficiency (FXPOI) and most recently, fragile X-associated neurodevelopmental disorders (FXAND) which commonly includes anxiety and depression. In addition to these associated disorders, extant literature and clinical observations have suggested an association between the premutation state and ASD. In this paper, we review the literature pertinent to this and discuss possible molecular mechanisms that may explain this association. This includes lowered levels of the FMR1 Protein (FMRP), GABA deficits, mitochondrial dysfunction and secondary genetic abnormalities that is seen in premutation carriers as well as their increased vulnerability to environmental stressors. Understanding these mechanisms can facilitate development of targeted treatment for specific sub-groups of ASD and premutation disorders in future.

GGC repeat expansion of RILPL1 is associated with oculopharyngodistal myopathy

OBJECTIVE

Oculopharyngodistal myopathy (OPDM) is an adult-onset neuromuscular disease characterized by progressive ptosis, dysarthria, ophthalmoplegia, and distal muscle weakness. Recent studies revealed GGC repeat expansions in 5'-UTR of LRP12, GIPC1, and NOTCH2NLC are associated with OPDM. Despite these advances, around 30% of OPDM patients remain genetically undiagnosed. Herein, we aim to investigate genetic basis for undiagnosed OPDM patients in two unrelated Chinese Han families.

METHODS

Parametric linkage analysis was performed. Long-read sequencing followed by repeat-primed polymerase chain reaction (RP-PCR) and amplicon length polymerase chain reaction (AL-PCR) were used to determine the genetic cause. Targeted methylation sequencing was implemented to detect epigenetic changes. The possible pathogenesis mechanism was investigated by qPCR, immunoblotting, RNA FISH, and immunofluorescence staining of muscle biopsy samples.

RESULTS

The disease locus was mapped to 12q24.3. Subsequently, GGC repeat expansion in the promoter region of RILPL1 was identified in six OPDM patients from two families, findings consistent with a founder effect, designated as OPDM type 4 (OPDM4). Targeted methylation sequencing revealed hypermethylation at RILPL1 locus in unaffected individuals with ultralong expansion. Analysis of muscle samples showed no significant differences in RILPL1 mRNA or RILPL1 protein levels between patients and controls. Public CAGE-seq data indicated that alternative TSSs exist upstream of the RefSeq-annotated RILPL1 TSS. Strand-specific RNAseq data revealed bidirectional transcription from the RILPL1 locus. Finally, FISH/IF indicated that both sense and antisense transcripts formed RNA foci and were co-localized with hnRNPA2B1 and p62 in the intranuclear inclusions of OPDM4 patients.

INTERPRETATION

Our findings implicate abnormal GGC repeat expansions in the promoter region of RILPL1 as a novel genetic cause for OPDM, and suggest a methylation mechanism and a potential RNA toxicity mechanism are involved in OPDM4 pathogenesis. This article is protected by copyright. All rights reserved.

The polyG diseases: a new disease entity

Recently, inspired by the similar clinical and pathological features shared with fragile X-associated tremor/ataxia syndrome (FXTAS), abnormal expansion of CGG repeats in the 5' untranslated region has been found in neuronal intranuclear inclusion disease (NIID), oculopharyngeal myopathy with leukoencephalopathy (OPML), and oculopharyngodistal myopathy (OPDMs). Although the upstream open reading frame has not been elucidated in OPML and OPDMs, polyglycine (polyG) translated by expanded CGG repeats is reported to be as a primary pathogenesis in FXTAS and NIID. Collectively, these findings indicate a new disease entity, the polyG diseases. In this review, we state the common clinical manifestations, pathological features, mechanisms, and potential therapies in these diseases, and provide preliminary opinions about future research in polyG diseases.

Prosaccade and Antisaccade Behavior in Fragile X-Associated Tremor/Ataxia Syndrome Progression

Background

Quantitative measurement of eye movements can reveal subtle progression in neurodegenerative diseases.

Objective

To determine if quantitative measurements of eye movements may reveal subtle progression of fragile X-associated tremor and ataxia (FXTAS).

Methods

Prosaccade (PS) and antisaccade (AS) behavior was analyzed in 25 controls, 57 non-FXTAS carriers, and 46 carriers with FXTAS.

Results

Symptomatic individuals with FXTAS had longer AS latencies, increased rates of AS errors, and increased AS dysmetria relative to non-FXTAS carriers and controls. These deficits, along with PS latency and velocity, were greater in advanced FXTAS stages.

Conclusion

AS deficits differentiated FXTAS from non-FXTAS premutation carriers implicating top-down control and frontostriatal deterioration. However, the absence of group differences between non-FXTAS carriers and controls in AS and PS markers suggests saccade performance may not be a sensitive enough measure for detecting conversion to FXTAS, but instead more helpful as translational biomarkers of FXTAS progression.

Cognitive Dysfunction in Repeat Expansion Diseases: A Review

With the development of the sequencing technique, more than 40 repeat expansion diseases (REDs) have been identified during the past two decades. Moreover, the clinical features of these diseases show some commonality, and the nervous system, especially the cognitive function was affected in part by these diseases. However, the specific cognitive domains impaired in different diseases were inconsistent. Here, we survey literature on the cognitive consequences of the following disorders presenting cognitive dysfunction and summarizing the pathogenic genes, epidemiology, and different domains affected by these diseases. We found that the cognitive domains affected in neuronal intranuclear inclusion disease (NIID) were widespread including the executive function, memory, information processing speed, attention, visuospatial function, and language. Patients with C9ORF72-frontotemporal dementia (FTD) showed impairment in executive function, memory, language, and visuospatial function. While in Huntington's disease (HD), the executive function, memory, and information processing speed were affected, in the fragile X-associated tremor/ataxia syndrome (FXTAS), executive function, memory, information processing speed, and attention were impaired. Moreover, the spinocerebellar ataxias showed broad damage in almost all the cognitive domains except for the relatively intact language ability. Some other diseases with relatively rare clinical data also indicated cognitive dysfunction, such as myotonic dystrophy type 1 (DM1), progressive myoclonus epilepsy (PME), Friedreich ataxia (FRDA), Huntington disease like-2 (HDL2), and cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). We drew a cognitive function landscape of the related REDs that might provide an aspect for differential diagnosis through cognitive domains and effective non-specific interventions for these diseases.

Uncovering Essential Tremor Genetics: The Promise of Long-Read Sequencing

Long-read sequencing (LRS) technologies have been recently introduced to overcome intrinsic limitations of widely-used next-generation sequencing (NGS) technologies, namely the sequencing limited to short-read fragments (150–300 base pairs). Since its introduction, LRS has permitted many successes in unraveling hidden mutational mechanisms. One area in clinical neurology in need of rethinking as it applies to genetic mechanisms is essential tremor (ET). This disorder, among the most common in neurology, is a syndrome often exhibiting an autosomal dominant pattern of inheritance whose large phenotypic spectrum suggest a multitude of genetic etiologies. Exome sequencing has revealed the genetic etiology only in rare ET families (FUS, SORT1, SCN4A, NOS3, KCNS2, HAPLN4/BRAL2, and USP46). We hypothesize that a reason for this shortcoming may be non-classical genetic mechanism(s) underpinning ET, among them trinucleotide, tetranucleotide, or pentanucleotide repeat disorders. In support of this hypothesis, trinucleotide (e.g., GGC repeats in NOTCH2NLC) and pentanucleotide repeat disorders (e.g., ATTTC repeats in STARD7) have been revealed as pathogenic in patients with a past history of what has come to be referred to as “ET plus,” bilateral hand tremor associated with epilepsy and/or leukoencephalopathy. A systematic review of LRS in neurodegenerative disorders showed that 10 of the 22 (45%) genetic etiologies ascertained by LRS include tremor in their phenotypic spectrum, suggesting that future clinical applications of LRS for tremor disorders may uncover genetic subtypes of familial ET that have eluded NGS, particularly those with associated leukoencephalopathy or family history of epilepsy. LRS provides a pathway for potentially uncovering novel genes and genetic mechanisms, helping narrow the large proportion of “idiopathic” ET.

Trinucleotide CGG Repeat Diseases: An Expanding Field of Polyglycine Proteins?

Microsatellites are repeated DNA sequences of 3–6 nucleotides highly variable in length and sequence and that have important roles in genomes regulation and evolution. However, expansion of a subset of these microsatellites over a threshold size is responsible of more than 50 human genetic diseases. Interestingly, some of these disorders are caused by expansions of similar sequences, sizes and localizations and present striking similarities in clinical manifestations and histopathological features, which suggest a common mechanism of disease. Notably, five identical CGG repeat expansions, but located in different genes, are the causes of fragile X-associated tremor/ataxia syndrome (FXTAS), neuronal intranuclear inclusion disease (NIID), oculopharyngodistal myopathy type 1 to 3 (OPDM1-3) and oculopharyngeal myopathy with leukoencephalopathy (OPML), which are neuromuscular and neurodegenerative syndromes with overlapping symptoms and similar histopathological features, notably the presence of characteristic eosinophilic ubiquitin-positive intranuclear inclusions. In this review we summarize recent finding in neuronal intranuclear inclusion disease and FXTAS, where the causing CGG expansions were found to be embedded within small upstream ORFs (uORFs), resulting in their translation into novel proteins containing a stretch of polyglycine (polyG). Importantly, expression of these polyG proteins is toxic in animal models and is sufficient to reproduce the formation of ubiquitin-positive intranuclear inclusions. These data suggest the existence of a novel class of human genetic pathology, the polyG diseases, and question whether a similar mechanism may exist in other diseases, notably in OPDM and OPML.

Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS): A Gender Perspective

Although larger trinucleotide expansions give rise to a neurodevelopmental disorder called fragile X syndrome, fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder caused by a “premutation” (55–200 CGG repeats) in the FMR1 gene. FXTAS is one of the more common single-gene forms of late-onset ataxia and tremor that may have a more complex development in women, with atypical presentations. After a brief presentation of the atypical case of an Italian woman with FXTAS, who had several paroxysmal episodes suggestive of acute cerebellar and/or brainstem dysfunction, this article will revise the phenotype of FXTAS in women. Especially in females, FXTAS has a broad spectrum of symptoms, ranging from relatively severe diseases in mid-adulthood to mild cases beginning in later life. Female FXTAS and male FXTAS have a different symptomatic spectrum, and studies on the fragile X premutation should be conducted separately on women or men. Hopefully, a better understanding of the molecular processes involved in the polymorphic features of FXTAS will lead to more specific and effective therapies for this complex disorder.

Neurodegenerative diseases associated with non-coding CGG tandem repeat expansions

Non-coding CGG repeat expansions cause multiple neurodegenerative disorders, including fragile X-associated tremor/ataxia syndrome, neuronal intranuclear inclusion disease, oculopharyngeal myopathy with leukodystrophy, and oculopharyngodistal myopathy. The underlying genetic causes of several of these diseases have been identified only in the past 2-3 years. These expansion disorders have substantial overlapping clinical, neuroimaging and histopathological features. The shared features suggest common mechanisms that could have implications for the development of therapies for this group of diseases - similar therapeutic strategies or drugs may be effective for various neurodegenerative disorders induced by non-coding CGG expansions. In this Review, we provide an overview of clinical and pathological features of these CGG repeat expansion diseases and consider the likely pathological mechanisms, including RNA toxicity, CGG repeat-associated non-AUG-initiated translation, protein aggregation and mitochondrial impairment. We then discuss future research needed to improve the identification and diagnosis of CGG repeat expansion diseases, to improve modelling of these diseases and to understand their pathogenesis. We also consider possible therapeutic strategies. Finally, we propose that CGG repeat expansion diseases may represent manifestations of a single underlying neuromyodegenerative syndrome in which different organs are affected to different extents depending on the gene location of the repeat expansion.

Non-Mendelian inheritance patterns and extreme deviation rates of CGG repeats in autism

As expansions of CGG short tandem repeats (STRs) are established as the genetic etiology of many neurodevelopmental disorders, we aimed to elucidate the inheritance patterns and role of CGG STRs in autism-spectrum disorder (ASD). By genotyping 6063 CGG STR loci in a large cohort of trios and quads with an ASD-affected proband, we determined an unprecedented rate of CGG repeat length deviation across a single generation. Although the concept of repeat length being linked to deviation rate was solidified, we show how shorter STRs display greater degrees of size variation. We observed that CGG STRs did not segregate by Mendelian principles but with a bias against longer repeats, which appeared to magnify as repeat length increased. Through logistic regression, we identified 19 genes that displayed significantly higher rates and degrees of CGG STR expansion within the ASD-affected probands (P < 1 × 10^-5). This study not only highlights novel repeat expansions that may play a role in ASD but also reinforces the hypothesis that CGG STRs are specifically linked to human cognition.

Eye Movements in Fragile X-Associated Tremor/Ataxia Syndrome

BACKGROUND

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder characterized by ataxia, tremor, and parkinsonism. Eye motility abnormalities on the clinical examination of FXTAS patients have not been formally studied.

METHODS

A case-control study with fragile X gene mutation carriers with and without FXTAS and normal controls was conducted and included a videotaping of ocular items of the International Cooperative Ataxia Rating Scale (ICARS). A neuro-ophthalmologist blinded to gene status rated nystagmus, ocular pursuit, and saccades.

RESULTS

Forty-four cases and controls were recruited, with an average age of 55.2 years (±7.4) and 57% women. Gaze-evoked nystagmus was increased in fragile X gene carriers (odds ratio 1.44, 95% confidence interval: 0.33-7.36) but was not statistically significant. There was no difference in ocular pursuit nor saccade dysmetria between cases and controls.

CONCLUSION

The results show that clinical examination findings of ocular abnormalities, using the ICARS oculomotor disorders movement subscale, are not more common in FXTAS or FMR1 premutation carriers than normal controls on examination in the clinic. Examining a larger cohort of patients with FXTAS would be an ideal next step.

Frequency of FMR1 Premutation Alleles in Patients with Undiagnosed Cerebellar Ataxia and Multiple System Atrophy in the Japanese Population

Fragile X-associated tremor/ataxia syndrome (FXTAS) is an adult-onset neurodegenerative disorder caused by FMR1 premutation expansion of CGG repeats. FXTAS can be misdiagnosed with many neurodegenerative disorders manifesting with cerebellar ataxias owing to their overlapping clinical and radiological features. The frequency of the FMR1 premutation allele in Japan has not been fully determined. Herein, we aimed to determine the frequency of FMR1 premutation alleles in Japanese patients with undiagnosed cerebellar ataxia and multiple system atrophy, using repeat-primed PCR in 186 patients with adult onset of undiagnosed cerebellar ataxia and 668 patients with multiple system atrophy, to identify expanded CGG repeats as well as to detect AGG interruptions within the expanded alleles. The size of expansions was estimated using fragment length analysis of PCR products obtained by conventional PCR employing a pair of unique primers flanking the repeat sequence. We identified FMR1 premutation alleles in three male patients. One patient revealed 84 repeat units with one AGG interruption and another patient showed 103 repeat units. Both had presented with sporadic cerebellar ataxia, giving an estimated frequency of 3.7% among Japanese male patients with sporadic cerebellar ataxia with age at onset above 50 years. One patient with the clinical diagnosis of multiple system atrophy harbored 60 repeat units with four AGG interruptions. FMR1 intermediate alleles were observed in two males and one female among the multiple system atrophy patients. We found that genetic tests for FMR1 premutation should be considered in Japanese male patients with cerebellar ataxia with the age at onset above 50 years.

SRSF protein kinase 1 modulates RAN translation and suppresses CGG repeat toxicity

Transcribed CGG repeat expansions cause neurodegeneration in Fragile X-associated tremor/ataxia syndrome (FXTAS). CGG repeat RNAs sequester RNA-binding proteins (RBPs) into nuclear foci and undergo repeat-associated non-AUG (RAN) translation into toxic peptides. To identify proteins involved in these processes, we employed a CGG repeat RNA-tagging system to capture repeat-associated RBPs by mass spectrometry in mammalian cells. We identified several SR (serine/arginine-rich) proteins that interact selectively with CGG repeats basally and under cellular stress. These proteins modify toxicity in a Drosophila model of FXTAS. Pharmacologic inhibition of serine/arginine protein kinases (SRPKs), which alter SRSF protein phosphorylation, localization, and activity, directly inhibits RAN translation of CGG and GGGGCC repeats (associated with C9orf72 ALS/FTD) and triggers repeat RNA retention in the nucleus. Lowering SRPK expression suppressed toxicity in both FXTAS and C9orf72 ALS/FTD model flies, and SRPK inhibitors suppressed CGG repeat toxicity in rodent neurons. Together, these findings demonstrate roles for CGG repeat RNA binding proteins in RAN translation and repeat toxicity and support further evaluation of SRPK inhibitors in modulating RAN translation associated with repeat expansion disorders.

Parkinsonism and tremor syndromes

Tremor, the most common movement disorder, may occur in isolation or may co-exist with a variety of other neurologic and movement disorders including parkinsonism, dystonia, and ataxia. When associated with Parkinson's disease, tremor may be present at rest or as an action tremor overlapping in phenomenology with essential tremor. Essential tremor may be associated not only with parkinsonism but other neurological disorders, suggesting the possibility of essential tremor subtypes. Besides Parkinson's disease, tremor can be an important feature of other parkinsonian disorders, such as atypical parkinsonism and drug-induced parkinsonism. In addition, tremor can be a prominent feature in patients with other movement disorders such as fragile X-associated tremor/ataxia syndrome, and Wilson's disease in which parkinsonian features may be present. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

Parkinsonism and ataxia

Ataxia is not a common feature in Parkinson's disease. Nevertheless, some rare forms of parkinsonism have ataxia as one of the main features in their clinical picture, especially those with juvenile or early-onset. On the other side, in cerebellar degenerative diseases, parkinsonism might accompany the typical symptoms and even become predominant in some cases. Many disorders involving different neurological systems present with a movement phenomenology reflecting the underlying pattern of pathological involvement, such as neurodegeneration with brain iron accumulation, neurodegeneration associated with calcium deposition, and metabolic and mitochondrial disorders. The prototype of sporadic disorders that present with a constellation of symptoms due to the involvement of multiple Central Nervous System regions is multiple system atrophy, whose motor symptoms at onset can be cerebellar ataxia or parkinsonism. Clinical syndromes encompassing both parkinsonian and cerebellar features might represent a diagnostic challenge for neurologists. Recognizing acquired and potentially treatable causes responsible for complex movement disorders is of paramount importance, since an early diagnosis is essential to prevent permanent consequences. The present review aims to provide a pragmatic overview of the most common diseases characterized by the coexistence of cerebellar and parkinsonism features and suggests a possible diagnostic approach for both inherited and sporadic disorders. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

Persistence of cerebellar ataxia during chronic ethanol exposure is associated with epigenetic up-regulation of Fmr1 gene expression in rat cerebellum

BACKGROUND

Alcohol intoxication produces ataxia by affecting the cerebellum, which coordinates movements. Fragile X mental retardation (FMR) protein is a complex regulator of RNA and synaptic plasticity implicated in fragile X-associated tremor/ataxia syndrome, which features ataxia and increased Fmr1 mRNA expression resulting from epigenetic dysregulation of FMRP. We recently demonstrated that acute ethanol-induced ataxia is associated with increased cerebellar Fmr1 gene expression via histone modifications in rats, but it is unknown whether similar behavioral and molecular changes occur following chronic ethanol exposure. Here, we investigated the effects of chronic ethanol exposure on ataxia and epigenetically regulated changes in Fmr1 expression in the cerebellum.

METHODS

Male adult Sprague-Dawley rats were trained on the accelerating rotarod and then fed with chronic ethanol or a control Lieber-DeCarli diet while undergoing periodic behavioral testing for ataxia during ethanol exposure and withdrawal. Cerebellar tissues were analyzed for expression of the Fmr1 gene and its targets using a real-time quantitative polymerase chain reaction assay. The epigenetic regulation of Fmr1 was also investigated using a chromatin immunoprecipitation assay.

RESULTS

Ataxic behavior measured by the accelerating rotarod behavioral test developed during chronic ethanol treatment and persisted at both the 8-h and 24-h withdrawal time points compared to control diet-fed rats. In addition, chronic ethanol treatment resulted in up-regulated expression of Fmr1 mRNA and increased activating epigenetic marks H3K27 acetylation and H3K4 trimethylation at 2 sites within the Fmr1 promoter. Finally, measurement of the expression of relevant FMRP mRNA targets in the cerebellum showed that chronic ethanol up-regulated cAMP response element binding (CREB) Creb1, Psd95, Grm5, and Grin2b mRNA expression without altering Grin2a, Eaa1, or histone acetyltransferases CREB binding protein (Cbp) or p300 mRNA transcripts.

CONCLUSIONS

These results suggest that epigenetic regulation of Fmr1 and subsequent FMRP regulation of target mRNA transcripts constitute neuroadaptations in the cerebellum that may underlie the persistence of ataxic behavior during chronic ethanol exposure and withdrawal.

Case Report: Coexistence of Alzheimer-Type Neuropathology in Fragile X-Associated Tremor Ataxia Syndrome

This case documents the co-occurrence of the fragile X-associated tremor ataxia syndrome (FXTAS) and Alzheimer-type neuropathology in a 71-year-old premutation carrier with 85 CGG repeats in the fragile X mental retardation 1 (FMR1) gene, in addition to an apolipoprotein E (APOE) ε4 allele. FXTAS and Alzheimer's Disease (AD) are late-onset neurodegenerative diseases that share overlapping cognitive deficits including processing speed, working memory and executive function. The prevalence of coexistent FXTAS-AD pathology remains unknown. The clinical picture in this case was marked with rapid cognitive decline between age 67 and 71 years in addition to remarkable MRI changes. Over the 16 months between the two clinical evaluations, the brain atrophied 4.12% while the lateral ventricles increased 26.4% and white matter hyperintensities (WMH) volume increased 15.6%. Other regions atrophied substantially faster than the whole brain included the thalamus (-6.28%), globus pallidus (-10.95%), hippocampus (-6.95%), and amygdala (-7.58%). A detailed postmortem assessment included an MRI with confluent WMH and evidence of cerebral microbleeds (CMB). The histopathological study demonstrated FXTAS inclusions in neurons and astrocytes, a widespread presence of phosphorylated tau protein and, amyloid β plaques in cortical areas and the hippocampus. CMBs were noticed in the precentral gyrus, middle temporal gyrus, visual cortex, and brainstem. There were high amounts of iron deposits in the globus pallidus and the putamen consistent with MRI findings. We hypothesize that coexistent FXTAS-AD neuropathology contributed to the steep decline in cognitive abilities.

Sulforaphane improves mitochondrial metabolism in fibroblasts from patients with fragile X-associated tremor and ataxia syndrome

CGG expansions between 55 and 200 in the 5'-untranslated region of the fragile-X mental retardation gene (FMR1) increase the risk of developing the late-onset debilitating neuromuscular disease Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS). While the science behind this mutation, as a paradigm for RNA-mediated nucleotide triplet repeat expansion diseases, has progressed rapidly, no treatment has proven effective at delaying the onset or decreasing morbidity, especially at later stages of the disease. Here, we demonstrated the beneficial effect of the phytochemical sulforaphane (SFN), exerted through NRF2-dependent and independent manner, on pathways relevant to brain function, bioenergetics, unfolded protein response, proteosome, antioxidant defenses, and iron metabolism in fibroblasts from FXTAS-affected subjects at all disease stages. This study paves the way for future clinical studies with SFN in the treatment of FXTAS, substantiated by the established use of this agent in clinical trials of diseases with NRF2 dysregulation and in which age is the leading risk factor.

Deciphering Neurodegenerative Diseases Using Long-Read Sequencing

Neurodegenerative diseases exhibit chronic progressive lesions in the central and peripheral nervous systems with unclear causes. The search for pathogenic mutations in human neurodegenerative diseases has benefited from massively parallel short-read sequencers. However, genomic regions, including repetitive elements, especially with high/low GC content, are far beyond the capability of conventional approaches. Recently, long-read single-molecule DNA sequencing technologies have emerged and enabled researchers to study genomes, transcriptomes, and metagenomes at unprecedented resolutions. The identification of novel mutations in unresolved neurodegenerative disorders, the characterization of causative repeat expansions, and the direct detection of epigenetic modifications on naive DNA by virtue of long-read sequencers will further expand our understanding of neurodegenerative diseases. In this article, we review and compare 2 prevailing long-read sequencing technologies, Pacific Biosciences and Oxford Nanopore Technologies, and discuss their applications in neurodegenerative diseases.

Cyclic mismatch binding ligands interact with disease-associated CGG trinucleotide repeats in RNA and suppress their translation

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder caused by a limited expansion of CGG repeats in the FMR1 gene. Degeneration of neurons in FXTAS cell models can be triggered by accumulation of polyglycine protein (FMRpolyG), a by-product of translation initiated upstream to the repeats. Specific aims of our work included testing if naphthyridine-based molecules could (i) block FMRpolyG synthesis by binding to CGG repeats in RNA, (ii) reverse pathological alterations in affected cells and (iii) preserve the content of FMRP, translated from the same FMR1 mRNA. We demonstrate that cyclic mismatch binding ligand CMBL4c binds to RNA structure formed by CGG repeats and attenuates translation of FMRpolyG and formation of nuclear inclusions in cells transfected with vectors expressing RNA with expanded CGG repeats. Moreover, our results indicate that CMBL4c delivery can reduce FMRpolyG-mediated cytotoxicity and apoptosis. Importantly, its therapeutic potential is also observed once the inclusions are already formed. We also show that CMBL4c-driven FMRpolyG loss is accompanied by partial FMRP reduction. As complete loss of FMRP induces FXS in children, future experiments should aim at evaluation of CMBL4c therapeutic intervention in differentiated tissues, in which FMRpolyG translation inhibition might outweigh adverse effects related to FMRP depletion.

The Phenotypic Profile Associated With the FMR1 Premutation in Women: An Investigation of Clinical-Behavioral, Social-Cognitive, and Executive Abilities

The FMR1 gene in its premutation (PM) state has been linked to a range of clinical and subclinical phenotypes among FMR1 PM carriers, including some subclinical traits associated with autism spectrum disorder (ASD). This study attempted to further characterize the phenotypic profile associated with the FMR1 PM by studying a battery of assessments examining clinical-behavioral traits, social-cognitive, and executive abilities in women carrying the FMR1 PM, and associations with FMR1-related variability. Participants included 152 female FMR1 PM carriers and 75 female controls who were similar in age and IQ, and screened for neuromotor impairments or signs of fragile X-associated tremor/ataxia syndrome. The phenotypic battery included assessments of ASD-related personality and language (i.e., pragmatic) traits, symptoms of anxiety and depression, four different social-cognitive tasks that tapped the ability to read internal states and emotions based on different cues (e.g., facial expressions, biological motion, and complex social scenes), and a measure of executive function. Results revealed a complex phenotypic profile among the PM carrier group, where subtle differences were observed in pragmatic language, executive function, and social-cognitive tasks that involved evaluating basic emotions and trustworthiness. The PM carrier group also showed elevated rates of ASD-related personality traits. In contrast, PM carriers performed similarly to controls on social-cognitive tasks that involved reliance on faces and biological motion. The PM group did not differ from controls on self-reported depression or anxiety symptoms. Using latent profile analysis, we observed three distinct subgroups of PM carriers who varied considerably in their performance across tasks. Among PM carriers, CGG repeat length was a significant predictor of pragmatic language violations. Results suggest a nuanced phenotypic profile characterized by subtle differences in select clinical-behavioral, social-cognitive, and executive abilities associated with the FMR1 PM in women.

Cerebral Microbleeds in Fragile X-Associated Tremor/Ataxia Syndrome

BACKGROUND

Fragile X-associated tremor/ataxia syndrome is a neurodegenerative disease of late onset developed by carriers of the premutation in the fragile x mental retardation 1 (FMR1) gene. Pathological features of neurodegeneration in fragile X-associated tremor/ataxia syndrome include toxic levels of FMR1 mRNA, ubiquitin-positive intranuclear inclusions, white matter disease, iron accumulation, and a proinflammatory state.

OBJECTIVE

The objective of this study was to analyze the presence of cerebral microbleeds in the brains of patients with fragile X-associated tremor/ataxia syndrome and investigate plausible causes for cerebral microbleeds in fragile X-associated tremor/ataxia syndrome.

METHODS

We collected cerebral and cerebellar tissue from 15 fragile X-associated tremor/ataxia syndrome cases and 15 control cases carrying FMR1 normal alleles. We performed hematoxylin and eosin, Perls and Congo red stains, ubiquitin, and amyloid β protein immunostaining. We quantified the number of cerebral microbleeds, amount of iron, presence of amyloid β within the capillaries, and number of endothelial cells containing intranuclear inclusions. We evaluated the relationships between pathological findings using correlation analysis.

RESULTS

We found intranuclear inclusions in the endothelial cells of capillaries and an increased number of cerebral microbleeds in the brains of those with fragile X-associated tremor/ataxia syndrome, both of which are indicators of cerebrovascular dysfunction. We also found a suggestive association between the amount of capillaries that contain amyloid β in the cerebral cortex and the rate of disease progression.

CONCLUSION

We propose microangiopathy as a pathologic feature of fragile X-associated tremor/ataxia syndrome. © 2021 International Parkinson and Movement Disorder Society.

Men with FMR1 premutation alleles of less than 71 CGG repeats have low risk of being affected with fragile X-associated tremor/ataxia syndrome (FXTAS)

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset condition characterised by cerebellar ataxia and intention tremor, usually found in individuals with FMR1 premutation alleles (PM-CGG expansion of 55-199 repeats). Population studies estimate that between 1 in 250 and 1 in 1600 men have a PM, with up to 45% of these men suggested to develop FXTAS by age 80. We used a Bayesian approach to compare the probability of finding a specific PM genotype in an ataxia population to a population control group and found an estimated penetrance of <1% (0.031%; CI 0.007% to 0.141%) for men with ≤70 CGGs. These findings suggest that men with a PM of ≤70 CGGs, who comprise the vast majority of those with a PM, have a much lower risk of being affected with FXTAS than previously suggested. This is an issue of growing importance for accurate genetic counselling, as those with a PM of ≤70 CGGs are increasingly detected through community carrier screening or neurodevelopmental assessment programmes.