Treatment of fragile X-associated tremor ataxia syndrome (FXTAS) and related neurological problems

Fragile X syndrome in the largest world clustering. I. Genetic epidemiology and founder effect outline

The FMR1 5' regulation gene region harbors a CGG trinucleotide repeat expansion (CGG-TRE) that causes Fragile X syndrome (FXS) when it expands to more than 200 repetitions. Ricaurte is a small village in southwestern Colombia, with an FXS prevalence of 1 in 38 men and 1 in 100 women (~100 times higher than the worldwide reported prevalence), defining Ricaurte as the largest FXS cluster in the world. In the present study, using next-generation sequencing of whole exome capture, we genotype 55 individuals from Ricaurte (49 with either full mutation or with premutation), four individuals from neighboring villages (with either the full mutation or with the premutation), and one unaffected woman, native of Ricaurte, who did not belong to any of the affected families. With advanced clustering and haplotype reconstruction, we modeled a common haplotype of 33 SNPs spanning 83,567,899 bp and harboring the FMR1 gene. This reconstructed haplotype was found in all the men from Ricaurte who carried the expansion, demonstrating that the genetic conglomerate of FXS in this population is due to a founder effect. The definition of this founder effect and its population outlining will allow a better prediction, follow-up, precise and personalized characterization of epidemiological parameters, better knowledge of the disease's natural history, and confident improvement of the clinical attention, life quality, and health interventions for this community.

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.

Advances in the Diagnosis and Management of Psychotic Symptoms in Neurodegenerative Diseases: A Narrative Review

Background: Approximately 15% of older adults may experience psychotic phenomena. Primary psychiatric disorders that manifest with psychosis (delusions, hallucinations, and disorganized thought or behavior) account for less than half. Up to 60% of late-life psychotic symptoms are due to systemic medical or neurological conditions, particularly neurodegenerative diseases. A thorough medical workup including laboratory tests, additional procedures if indicated, and neuroimaging studies is recommended. This narrative review summarizes current evidence regarding the epidemiology and phenomenology of psychotic symptoms encountered as part of the neurodegenerative disease continuum (including prodromal and manifest stages). Results: Prodromes are constellations of symptoms that precede the onset of overt neurodegenerative syndromes. Prodromal psychotic features, particularly delusions, have been associated with an increased likelihood of receiving a neurodegenerative disease diagnosis within several years. Prompt prodrome recognition is crucial for early intervention. The management of psychosis associated with neurodegenerative diseases includes behavioral and somatic strategies, although evidence is scarce and mostly limited to case reports, case series, or expert consensus guidelines, with few randomized controlled trials. Conclusion: The complexity of psychotic manifestations warrants management by interprofessional teams that provide coordinated, integrated care.

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.

A longitudinal investigation of pragmatic language across contexts in autism and related neurodevelopmental conditions

Background

Pragmatic language, or the use of language in social contexts, is a critical skill in daily life, supporting social interactions and the development of meaningful social relationships. Pragmatic language is universally impacted in autism spectrum disorder (ASD) and pragmatic deficits are also common in other neurodevelopmental conditions, particularly those related to ASD, such as fragile X syndrome (FXS). This study used a multi-method, longitudinal approach to characterize potentially unique pragmatic profiles across different neurodevelopmental disabilities, and across contexts that varied in degree of social demand. The utility of computational linguistic analyses, as an efficient tool for capturing pragmatic abilities, was also explored.

Methods

Pragmatic skills of boys with idiopathic ASD (ASD-O, n = 43), FXS with and without ASD (FXS-ASD, n = 57; FXS-O, n = 14), Down syndrome (DS, n = 22), and typical development (TD, n = 24) were compared using variables obtained from a standardized measure, narrative, and semi-naturalistic conversation at up to three time points.

Results

Pragmatic language was most significantly impacted among males with ASD-O and FXS-ASD across all three contexts, with more difficulties in the least structured context (conversation), and also some differences based on FXS comorbidity. Patterns of group differences were more nuanced for boys with FXS-O and DS, with context having less of an impact. Clinical groups demonstrated minimal changes in pragmatic skills with age, with some exceptions. Computational language measurement tools showed some utility for measuring pragmatic skills, but were not as successful as traditional methods at capturing differences between clinical groups.

Conclusion

Overlap and differences between ASD and other forms of neurodevelopmental disability in general, and between idiopathic and syndromic ASD in particular, have important implications for developing precisely tailored assessment and intervention approaches, consistent with a personalized medicine approach to clinical study and care in ASD.

Allopregnanolone Improves Locomotor Activity and Arousal in the Aged CGG Knock-in Mouse Model of Fragile X-Associated Tremor/Ataxia Syndrome

Carriers of the fragile X premutation (PM) can develop a variety of early neurological symptoms, including depression, anxiety and cognitive impairment as well as being at risk for developing the late-onset fragile X-associated tremor/ataxia syndrome (FXTAS). The absence of effective treatments for FXTAS underscores the importance of developing efficacious therapies to reduce the neurological symptoms in elderly PM carriers and FXTAS patients. A recent preliminary study reported that weekly infusions of Allopregnanolone (Allop) may improve deficits in executive function, learning and memory in FXTAS patients. Based on this study we examined whether Allop would improve neurological function in the aged CGG knock-in (CGG KI) dutch mouse, B6.129P2(Cg)-Fmr1^tm2Cgr/Cgr, that models much of the symptomatology in PM carriers and FXTAS patients. Wild type and CGG KI mice received 10 weekly injections of Allop (10 mg/kg, s.c.), followed by a battery of behavioral tests of motor function, anxiety, and repetitive behavior, and 5-bromo-2'-deoxyuridine (BrdU) labeling to examine adult neurogenesis. The results provided evidence that Allop in CGG KI mice normalized motor performance and reduced thigmotaxis in the open field, normalized repetitive digging behavior in the marble burying test, but did not appear to increase adult neurogenesis in the hippocampus. Considered together, these results support further examination of Allop as a therapeutic strategy in patients with FXTAS.

Characterization of the Metabolic, Clinical and Neuropsychological Phenotype of Female Carriers of the Premutation in the X-Linked FMR1 Gene

The X-linked FMR1 premutation (PM) is characterized by a 55-200 CGG triplet expansion in the 5'-untranslated region (UTR). Carriers of the PM were originally thought to be asymptomatic; however, they may present general neuropsychiatric manifestations including learning disabilities, depression and anxiety, among others. With age, both sexes may also develop the neurodegenerative disease fragile X-associated tremor/ataxia syndrome (FXTAS). Among carriers, females are at higher risk for developing immune disorders, hypertension, seizures, endocrine disorders and chronic pain, among others. Some female carriers younger than 40 years old may develop fragile X-associated primary ovarian insufficiency (FXPOI). To date, no studies have addressed the metabolic footprint - that includes mitochondrial metabolism - of female carriers and its link to clinical/cognitive manifestations. To this end, we performed a comprehensive biochemical assessment of 42 female carriers (24-70 years old) compared to sex-matched non-carriers. By applying a multivariable correlation matrix, a generalized bioenergetics impairment was correlated with diagnoses of the PM, FXTAS and its severity, FXPOI and anxiety. Intellectual deficits were strongly correlated with both mitochondrial dysfunction and with CGG repeat length. A combined multi-omics approach identified a down-regulation of RNA and mRNA metabolism, translation, carbon and protein metabolism, unfolded protein response, and up-regulation of glycolysis and antioxidant response. The suboptimal activation of the unfolded protein response (UPR) and endoplasmic-reticulum-associated protein degradation (ERAD) response challenges and further compromises the PM genetic background to withstand other, more severe forms of stress. Mechanistically, some of the deficits were linked to an altered protein expression due to decreased protein translation, but others seemed secondary to oxidative stress originated from the accumulation of either toxic mRNA or RAN-derived protein products or as a result of a direct toxicity of accumulated metabolites from deficiencies in critical enzymes.

Quantification of Neural Activity in FMR1 Premutation Carriers during a Dynamic Sway Task using Source Localization

Fragile X-associated Tremor/Ataxia Syndrome is a genetic neurodegenerative disorder affecting carriers of the FMR1 premutation. Not all carriers develop the condition and the age of onset is somewhat variable. A greater understanding of disease progression would be beneficial. Eight carriers and five controls matched by age, sex, and dominant hand volunteered to perform a sway task on a force platform while EEG was simultaneously recorded. Sway parameters were extracted from the movement data at important timepoints throughout their sway cycles and matched to their EEG activity. Distributed source analysis was applied. While there initially appeared to be differences in neural activity between the two groups in the anterior lobe, the right posterior lobe, the right superior parietal lobule and the right parietal lobe, these differences did not survive correction for multiple comparisons.

Elevated FMR1-mRNA and lowered FMRP - A double-hit mechanism for psychiatric features in men with FMR1 premutations

Fragile X syndrome (FXS) is caused by a full mutation of the FMR1 gene (>200 CGG repeats and subsequent methylation), such that there is little or no FMR1 protein (FMRP) produced, leading to intellectual disability (ID). Individuals with the premutation allele (55-200 CGG repeats, generally unmethylated) have elevated FMR1 mRNA levels, a consequence of enhanced transcription, resulting in neuronal toxicity and a spectrum of premutation-associated disorders, including the neurodegenerative disorder fragile X-associated tremor/ataxia syndrome (FXTAS). Here we described 14 patients who had both lowered FMRP and elevated FMR1 mRNA levels, representing dual mechanisms of clinical involvement, which may combine features of both FXS and FXTAS. In addition, the majority of these cases show psychiatric symptoms, including bipolar disorder, and/or psychotic features, which are rarely seen in those with just FXS.

Oxidative Stress in DNA Repeat Expansion Disorders: A Focus on NRF2 Signaling Involvement

DNA repeat expansion disorders are a group of neuromuscular and neurodegenerative diseases that arise from the inheritance of long tracts of nucleotide repetitions, located in the regulatory region, introns, or inside the coding sequence of a gene. Although loss of protein expression and/or the gain of function of its transcribed mRNA or translated product represent the major pathogenic effect of these pathologies, mitochondrial dysfunction and imbalance in redox homeostasis are reported as common features in these disorders, deeply affecting their severity and progression. In this review, we examine the role that the redox imbalance plays in the pathological mechanisms of DNA expansion disorders and the recent advances on antioxidant treatments, particularly focusing on the expression and the activity of the transcription factor NRF2, the main cellular regulator of the antioxidant response.

Parkinsonism Versus Concomitant Parkinson's Disease in Fragile X-Associated Tremor/Ataxia Syndrome

BACKGROUND

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder associated with premutation alleles (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene. FXTAS is characterized by the presence of ubiquitin-positive inclusions in neurons and astrocytes and by cerebellar tremor and ataxia. Parkinsonism has been reported in FXTAS, but most patients lack the characteristic rest tremor and severe rigidity seen in idiopathic Parkinson's disease (PD).

OBJECTIVE

To describe the frequency of concomitant PD in FXTAS.

METHODS

We reviewed the medical record of 40 deceased patients diagnosed with FXTAS and performed a pathology analysis to confirm both FXTAS and PD.

RESULTS

Clinical histories indicated that 5 FXTAS patients were diagnosed with idiopathic PD and 2 with atypical parkinsonian syndrome. After pathological examination, we found that 7 patients in the PD clinical diagnosis group had dopaminergic neuronal loss; however, only 2 of 7 presented Lewy bodies (LBs) in the substantia nigra. Therefore, a total of 5% of the 40 cohort patients met the pathologic criteria for the concomitant diagnosis of FXTAS and PD. In addition, 2 patients not clinically diagnosed with PD also had nigral neuronal loss with LBs in substantia nigra. In total 10% of these 40 patients had LBs.

CONCLUSION

This report expands our understanding of clinical symptoms and unusual presentations in patients with FXTAS and the concept that the parkinsonism found in FXTAS is sometimes indistinguishable from PD. We propose that FMR1 should be recognized as one of the exceptional genetic causes of parkinsonism with presynaptic dopaminergic loss and LBs.

Placebo Response in Fragile X-associated Tremor/Ataxia Syndrome

BACKGROUND

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder characterized by intention tremor, cerebellar ataxia, and executive dysfunction in carriers of a CGG repeat expansion premutation (55-200 repeats) in the fragile X mental retardation 1 (FMR1) gene. Given reports of poor insight in FXTAS, we postulated that patients with FXTAS would be less likely to exhibit placebo response.

OBJECTIVE

To analyze placebo response from the first randomized controlled trial in FXTAS that evaluated cognitive and motor outcomes after 1 year of treatment with memantine.

METHODS

Data from the placebo arm of the first randomized controlled trial in FXTAS were analyzed. There were 2 coprimary outcomes. Based on studies in Parkinson's disease, placebo responders were defined as individuals with an improvement of at least 50% in the coprimary outcomes. Improvements of 20% and 30% served as secondary cutoff values based on the suggested magnitude of placebo response in other movement disorders.

RESULTS

A total of 36 participants in the placebo group completed baseline and follow-up evaluations. The average age was 66 ± 7 years, and 60% were men. Average CGG repeat size was 86 ± 18. A total of 19 participants had stage 3 disease. Only 1 patient showed 50% improvement in both coprimary outcomes. At 30% and 20% improvement, there were 2 and 3 patients showing placebo response in the coprimary outcomes, respectively.

CONCLUSIONS

Patients with FXTAS exhibited low rates of placebo response in a randomized controlled trial. Further studies on the relationship between baseline insight and placebo responsivity are applicable to FXTAS and other disorders exhibiting cognitive impairment.

Interaction between ventricular expansion and structural changes in the corpus callosum and putamen in males with FMR1 normal and premutation alleles

Ventricular enlargement (VE) is commonly observed in aging and fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative disorder. VE may generate a mechanical force causing structural deformation. In this longitudinal study, we examined the relationships between VE and structural changes in the corpus callosum (CC) and putamen. MRI scans (2-7/person over 0.2-7.5 years) were acquired from 22 healthy controls, 26 unaffected premutation carriers (PFX-), and 39 carriers affected with FXTAS (PFX+). Compared with controls, PFX- demonstrated enlarged fourth ventricles, whereas PFX+ displayed enlargement in both third and fourth ventricles, CC thinning, putamen atrophy/deformation (thinning and increased distance), and accelerated expansions in lateral ventricles. Common for all groups, baseline VE predicted accelerated CC thinning and putamen atrophy/deformation and conversely, baseline CC and putamen atrophy/deformation and enlarged third and fourth ventricles predicted accelerated lateral ventricular expansion. The results suggest a progressive VE within the 4 ventricles as FXTAS develops and a deleterious cycle between VE and brain deformation that may commonly occur during aging and FXTAS progression but become accelerated in FXTAS.

The Comprehensive Management of Cerebellar Ataxia in Adults

PURPOSE OF REVIEW

In this review, we present the multidisciplinary approach to the management of the many neurological, medical, social, and emotional issues facing patients with cerebellar ataxia.

RECENT FINDINGS

Our holistic approach to treatment, developed over the past 25 years in the Massachusetts General Hospital Ataxia Unit, is centered on the compassionate care of the patient and their family, empowering them through engagement, and including the families as partners in the healing process. We present the management of ataxia in adults, beginning with establishing an accurate diagnosis, followed by treatment of the multiple symptoms seen in cerebellar disorders, with a view to maximizing quality of life and effectively living with the consequences of ataxia. We discuss the importance of a multidisciplinary approach to the management of ataxia, including medical and non-medical management and the evidence base that supports these interventions. We address the pharmacological treatment of ataxia, tremor, and other associated movement disorders; ophthalmological symptoms; bowel, bladder, and sexual symptoms; orthostatic hypotension; psychiatric and cognitive symptoms; neuromodulation, including deep brain stimulation; rehabilitation including physical therapy, occupational therapy and speech and language pathology and, as necessary, involving urology, psychiatry, and pain medicine. We discuss the role of palliative care in late-stage disease. The management of adults with ataxia is complex and a team-based approach is essential.

Deep brain stimulation in uncommon tremor disorders: indications, targets, and programming

BACKGROUND

In uncommon tremor disorders, clinical efficacy and optimal anatomical targets for deep brain stimulation (DBS) remain inadequately studied and insufficiently quantified.

METHODS

We performed a systematic review of PubMed.gov and ClinicalTrials.gov. Relevant articles were identified using the following keywords: "tremor", "Holmes tremor", "orthostatic tremor", "multiple sclerosis", "multiple sclerosis tremor", "neuropathy", "neuropathic tremor", "fragile X-associated tremor/ataxia syndrome", and "fragile X."

RESULTS

We identified a total of 263 cases treated with DBS for uncommon tremor disorders. Of these, 44 had Holmes tremor (HT), 18 orthostatic tremor (OT), 177 multiple sclerosis (MS)-associated tremor, 14 neuropathy-associated tremor, and 10 fragile X-associated tremor/ataxia syndrome (FXTAS). DBS resulted in favorable, albeit partial, clinical improvements in HT cases receiving Vim-DBS alone or in combination with additional targets. A sustained improvement was reported in OT cases treated with bilateral Vim-DBS, while the two cases treated with unilateral Vim-DBS demonstrated only a transient effect. MS-associated tremor responded to dual-target Vim-/VO-DBS, but the inability to account for the progression of MS-associated disability impeded the assessment of its long-term clinical efficacy. Neuropathy-associated tremor substantially improved with Vim-DBS. In FXTAS patients, while Vim-DBS was effective in improving tremor, equivocal results were observed in those with ataxia.

CONCLUSIONS

DBS of select targets may represent an effective therapeutic strategy for uncommon tremor disorders, although the level of evidence is currently in its incipient form and based on single cases or limited case series. An international registry is, therefore, warranted to clarify selection criteria, long-term results, and optimal surgical targets.

Cerebellar Mild Iron Accumulation in a Subset of FMR1 Premutation Carriers with FXTAS

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder associated with premutation alleles of the FMR1 gene. Iron is essential for many facets of cell metabolism in the brain but when altered is likely to contribute to the development of neurodegenerative diseases. We previously reported that iron accumulates in the choroid plexus and the putamen in FXTAS and that the level and distribution of key iron-binding proteins are also altered, suggesting a potential alteration of iron metabolism in the brain. Here, we hypothesize that iron metabolism is also altered in the FXTAS cerebellum. To test this hypothesis, we used cerebellum samples collected from FXTAS and control subjects and measured the amount of iron contained within the cerebellar cortex and dentate nucleus. We found that the number of iron deposits increased in the cerebellum only in a subset of cases of FXTAS. This accumulation is likely to be mediated by factors other than or in addition to CGG-repeat coupled pathology. Thus, iron deposition in the cerebellum cannot be used as a hallmark of FXTAS pathogenesis.

FMR1 premutation with Prader-Willi phenotype and fragile X-associated tremor/ataxia syndrome

This is a report of FMR1 premutation with Prader-Willi phenotype (PWP) and FXTAS. Although the PWP is common in fragile X syndrome (FXS), it has never been described in someone with the premutation. The patient presented intranuclear inclusions, severe obesity, hyperphagia, and ADHD symptoms, typical of the PWP in FXS. In addition, the autopsy revealed multiple architectural cortical abnormalities.

Endocrine Dysfunction in Female FMR1 Premutation Carriers: Characteristics and Association with Ill Health

Female FMR1 premutation carriers (PMC) have been suggested to be at greater risk of ill health, in particular endocrine dysfunction, compared to the general population. We set out to review the literature relating to endocrine dysfunction, including premature ovarian insufficiency (POI), in female PMCs, and then to consider whether endocrine dysfunction in itself may be predictive of other illnesses in female PMCs. A systematic review and pilot data from a semi-structured health questionnaire were used. Medline, Embase, and PsycInfo were searched for papers concerning PMCs and endocrine dysfunction. For the pilot study, self-reported diagnoses in females were compared between PMCs with endocrine dysfunction (n = 18), PMCs without endocrine dysfunction (n = 14), and individuals without the premutation (n = 15). Twenty-nine papers were identified in the review; the majority concerned POI and reduced fertility, which are consistently found to be more common in PMCs than controls. There was some evidence that thyroid dysfunction may occur more frequently in subgroups of PMCs and that those with endocrine difficulties have poorer health than those without. In the pilot study, PMCs with endocrine problems reported higher levels of fibromyalgia (p = 0.03), tremor (p = 0.03), headache (p = 0.01) and obsessive-compulsive disorder (p = 0.009) than either comparison group. Further larger scale research is warranted to determine whether female PMCs are at risk of endocrine disorders other than those associated with reproduction and whether endocrine dysfunction identifies a high-risk group for the presence of other health conditions.

Risk Factors for Cognitive Impairment in Fragile X-Associated Tremor/Ataxia Syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disease with motor, psychiatric, and cognitive manifestations that occurs in carriers of the fragile X mental retardation 1 ( FMR1) gene premutations. This was a retrospective chart review of 196 individuals (127 men and 69 women) with FXTAS. Forty-six (23%) participants were cognitively impaired, of whom 19 (10%) had dementia. Risk factors for dementia were examined (CGG repeat size; alcohol, benzodiazepine, and opioid use; diabetes; hyperlipidemia; hypertension; hypothyroidism; obesity; sleep apnea; surgeries with general anesthesia; depression; family history of dementia). Thirteen individuals with FXTAS and dementia were then compared to 13 cognitively intact individuals matched on age, gender, and FXTAS stage. CGG repeat size was significantly higher (mean = 98.5, standard deviation [SD] = 22.2) in the dementia group, compared to the cognitively intact group (mean = 81.6, SD = 11.5; P = .0256). These results show that CGG repeat size is a risk factor for FXTAS dementia.

Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS) Motor Dysfunction Modeled in Mice

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that affects some carriers of the fragile X premutation (PM). In PM carriers, there is a moderate expansion of a CGG trinucleotide sequence (55-200 repeats) in the fragile X gene (FMR1) leading to increased FMR1 mRNA and small to moderate decreases in the fragile X mental retardation protein (FMRP) expression. The key symptoms of FXTAS include cerebellar gait ataxia, kinetic tremor, sensorimotor deficits, neuropsychiatric changes, and dementia. While the specific trigger(s) that causes PM carriers to progress to FXTAS pathogenesis remains elusive, the use of animal models has shed light on the underlying neurobiology of the altered pathways involved in disease development. In this review, we examine the current use of mouse models to study PM and FXTAS, focusing on recent advances in the field. Specifically, we will discuss the construct, face, and predictive validities of these PM mouse models, the insights into the underlying disease mechanisms, and potential treatments.

The impact of FMR1 gene mutations on human reproduction and development: a systematic review

PURPOSE

This is a comprehensive review of the literature in this field attempting to put the FMR1 gene and its evaluation into context, both in general and for the reproductive health audience.

METHODS

Online database search of publications with systematic review of all papers relevant to ovarian reserve and assisted reproduction was done.

RESULTS

Relevant papers were identified and assessed, and an attempt was made to understand, rationalize and explain the divergent views in this field of study. Seminal and original illustrations were employed.

CONCLUSIONS

FMR1 is a highly conserved gene whose interpretation and effect on outcomes remains controversial in the reproductive health setting. Recent re-evaluations of the commonly accepted normal range have yielded interesting tools for possibly explaining unexpected outcomes in assisted reproduction. Fragile X investigations should perhaps become more routinely assessed in the reproductive health setting, particularly following a failed treatment cycle where oocyte quality is thought to be a contributing factor, or in the presence of a surprise finding of diminished ovarian reserve in a young patient.

Neuropsychiatry of fragile X-premutation carriers with and without fragile X-associated tremor-ataxia syndrome: implications for neuropsychology

OBJECTIVES

Clinical neuropsychologists benefit from clinical currency in recently ascertained neuropsychiatric illness, such as fragile X premutation (FXPM) disorders. The author reviewed the clinical literature through 2016 for neuropsychiatric phenotypes in FXPM disorders, including patients with fragile X-associated tremor/ataxia syndrome (FXTAS).

METHODS

A PubMed search using the search terms 'Fragile X,' 'Premutation,' 'Carriers,' 'Psychiatric,' 'Dementia,' 'Mood,' and 'Anxiety' for citations in the clinical literature through 2016 was reviewed for studies specifically examining the neuropsychiatric phenotype in FXPM patients. The relevant articles were classified according to specific neuropsychiatric syndromes, including child onset, adult onset with and without FXTAS, as well as common systemic comorbidities in FXPM patients.

RESULTS

Eighty-six articles were reviewed for the neuropsychiatric and other phenotypes in FXPM patients. The neuropsychiatric phenotype in FXPM patients is distinct from that of full mutation (Fragile X Syndrome) patients. FXTAS is associated with a specific cortical-subcortical major or mild neurocognitive disorder (NCD).

CONCLUSIONS

FXPM patients are at risk for neuropsychiatric illness. In addition, FXPM patients are at risk for other systemic conditions that should raise suspicion for FXPM-associated illnesses. Clinicians should consider a diagnosis of FXPM-associated neuropsychiatric illness when patients with specific clinical scenarios are encountered; especially in patient pedigrees consistent with a typical (often multigenerational) presentation of fragile X-associated conditions, confirmatory genetic testing should be considered. Clinical management should take into account the psychological challenges of a multigenerational genetic neuropsychiatric illness with a variable CNS and systemic clinical phenotype.

Fragile X-associated tremor/ataxia syndrome - features, mechanisms and management

Many physicians are unaware of the many phenotypes associated with the fragile X premutation, an expansion in the 5' untranslated region of the fragile X mental retardation 1 (FMR1) gene that consists of 55-200 CGG repeats. The most severe of these phenotypes is fragile X-associated tremor/ataxia syndrome (FXTAS), which occurs in the majority of ageing male premutation carriers but in fewer than 20% of ageing women with the premutation. The prevalence of the premutation is 1 in 150-300 females, and 1 in 400-850 males, so physicians are likely to see people affected by FXTAS. Fragile X DNA testing is broadly available in the Western world. The clinical phenotype of FXTAS at presentation can vary and includes intention tremor, cerebellar ataxia, neuropathic pain, memory and/or executive function deficits, parkinsonian features, and psychological disorders, such as depression, anxiety and/or apathy. FXTAS causes brain atrophy and white matter disease, usually in the middle cerebellar peduncles, the periventricular area, and the splenium and/or genu of the corpus callosum. Here, we review the complexities involved in the clinical management of FXTAS and consider how targeted treatment for these clinical features of FXTAS will result from advances in our understanding of the molecular mechanisms that underlie this neurodegenerative disorder. Such targeted approaches should also be more broadly applicable to earlier forms of clinical involvement among premutation carriers.

Deep brain stimulation for the treatment of uncommon tremor syndromes

Introduction: Deep brain stimulation (DBS) has become a standard therapy for the treatment of select cases of medication refractory essential tremor and Parkinson’s disease however the effectiveness and long-term outcomes of DBS in other uncommon and complex tremor syndromes has not been well established. Traditionally, the ventralis intermedius nucleus (VIM) of the thalamus has been considered the main target for medically intractable tremors; however alternative brain regions and improvements in stereotactic techniques and hardware may soon change the horizon for treatment of complex tremors.

Areas covered: In this article, we conducted a PubMed search using different combinations between the terms ‘Uncommon tremors’, ‘Dystonic tremor’, ‘Holmes tremor’ ‘Midbrain tremor’, ‘Rubral tremor’, ‘Cerebellar tremor’, ‘outflow tremor’, ‘Multiple Sclerosis tremor’, ‘Post-traumatic tremor’, ‘Neuropathic tremor’, and ‘Deep Brain Stimulation/DBS’. Additionally, we examined and summarized the current state of evolving interventions for treatment of complex tremor syndromes.

Expertcommentary: Recently reported interventions for rare tremors include stimulation of the posterior subthalamic area, globus pallidus internus, ventralis oralis anterior/posterior thalamic subnuclei, and the use of dual lead stimulation in one or more of these targets. Treatment should be individualized and dictated by tremor phenomenology and associated clinical features.

Deep brain stimulation or thalamotomy in fragile X-associated tremor/ataxia syndrome? Case report

We present the case of a 66-year-old man who has been treated for essential tremor since the age of 58. He developed mild cerebellar gait ataxia seven years after tremor onset. Moderate, global brain atrophy was identified on MRI scans. At the age of 68, only temporary tremor relief could be achieved by bilateral deep brain stimulation of the ventral intermedius nucleus of the thalamus. Bilateral stimulation of the subthalamic nucleus also resulted only in transient improvement. In the meantime, progressive gait ataxia and tetraataxia developed accompanied by other cerebellar symptoms, such as nystagmus and scanning speech. These correlated with progressive development of bilateral symmetric hyperintensity of the middle cerebellar peduncles on T2 weighted MRI scans. Genetic testing revealed premutation of the FMR1 gene, establishing the diagnosis of fragile X-associated tremor/ataxia syndrome. Although this is a rare disorder, it should be taken into consideration during preoperative evaluation of essential tremor. Postural tremor ceased two years later after thalamotomy on the left side, while kinetic tremor of the right hand also improved.

Improving Health Education for Women Who Carry an FMR1 Premutation

Women who carry an FMR1 (i.e., fragile X) premutation have specific health risks over their lifetime. However, little is known about their experience understanding these risks and navigating their health needs. The aim of this study was to use qualitative analysis to uncover both barriers and facilitators to personal healthcare using a framework of the Health Belief Model. Five focus groups were conducted with a total of 20 women who carry the FMR1 premutation using a semi-structured discussion guide. All sessions were transcribed verbatim and independently coded by two researchers. The coders used a deductive - inductive approach to determine the prominent themes related to the participants' experiences seeking healthcare for premutation-related conditions. Salient barriers to personal healthcare included difficult clinical translation of research findings, lack of knowledge among healthcare providers and among the women themselves, different priorities, and shortage of premutation-specific support and targeted educational materials. Facilitators included family members, national and community support organizations, research studies, compassionate physicians, and other premutation carriers. Addressing barriers to personal healthcare through up-to-date educational materials can help diminish misperceptions regarding health risks. Targeted educational materials will aid in information sharing and awareness for women who carry the FMR1 premutation and their physicians.

Cascade Screening for Fragile X Syndrome/CGG Repeat Expansions in Children Attending Special Education in Sri Lanka

Fragile X syndrome (FXS) is the commonest cause of inherited mental retardation and clinically presents with learning, emotional and behaviour problems. FXS is caused by expansion of cytosine-guanine-guanine (CGG) repeats present in the 5’ untranslated region of the FMR1 gene. The aim of this study was to screen children attending special education institutions in Sri Lanka to estimate the prevalence of CGG repeat expansions. The study population comprised a representative national sample of 850 children (540 males, 310 females) with 5 to 18 years of age from moderate to severe mental retardation of wide ranging aetiology. Screening for CGG repeat expansion was carried out on DNA extracted from buccal cells using 3’ direct triplet primed PCR followed by melting curve analysis. To identify the expanded status of screened positive samples, capillary electrophoresis, methylation specific PCR and Southern hybridization were carried out using venous blood samples. Prevalence of CGG repeat expansions was 2.2%. Further classification of the positive samples into FXS full mutation, pre-mutation and grey zone gave prevalence of 1.3%, 0.8% and 0.1% respectively. All positive cases were male. No females with FXS were detected in our study may have been due to the small sample size.

Dysregulated iron metabolism in the choroid plexus in fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder associated with premutation alleles of the FMR1 gene that is characterized by progressive action tremor, gait ataxia, and cognitive decline. Recent studies of mitochondrial dysfunction in FXTAS have suggested that iron dysregulation may be one component of disease pathogenesis. We tested the hypothesis that iron dysregulation is part of the pathogenic process in FXTAS. We analyzed postmortem choroid plexus from FXTAS and control subjects, and found that in FXTAS iron accumulated in the stroma, transferrin levels were decreased in the epithelial cells, and transferrin receptor 1 distribution was shifted from the basolateral membrane (control) to a predominantly intracellular location (FXTAS). In addition, ferroportin and ceruloplasmin were markedly decreased within the epithelial cells. These alterations have implications not only for understanding the pathophysiology of FXTAS, but also for the development of new clinical treatments that may incorporate selective iron chelation.

Clinical, molecular, and pharmacological aspects of FMR1 related disorders

BACKGROUND

Fragile X syndrome, the most common inherited cause of intellectual disability, is associated with a broad spectrum of disorders across different generations of a single family. This study reviews the clinical manifestations of fragile X-associated disorders as well as the spectrum of mutations of the fragile X mental retardation 1 gene (FMR1) and the neurobiology of the fragile X mental retardation protein (FMRP), and also provides an overview of the potential therapeutic targets and genetic counselling.

DEVELOPMENT

This disorder is caused by expansion of the CGG repeat (>200 repeats) in the 5 prime untranslated region of FMR1, resulting in a deficit or absence of FMRP. FMRP is an RNA-binding protein that regulates the translation of several genes that are important in synaptic plasticity and dendritic maturation. It is believed that CGG repeat expansions in the premutation range (55 to 200 repeats) elicit an increase in mRNA levels of FMR1, which may cause neuronal toxicity. These changes manifest clinically as developmental problems such as autism and learning disabilities as well as neurodegenerative diseases including fragile X-associated tremor/ataxia syndrome (FXTAS).

CONCLUSIONS

Advances in identifying the molecular basis of fragile X syndrome may help us understand the causes of neuropsychiatric disorders, and they will probably contribute to development of new and specific treatments.

Axonal neuropathy in female carriers of the fragile X premutation with fragile x-associated tremor ataxia syndrome

INTRODUCTION

In this study we examined whether females with the fragile X-associated tremor ataxia syndrome (FXTAS) and non-FXTAS premutation carriers have electrophysiological signs of underlying peripheral neuropathy.

METHODS

Nerve conduction studies (NCS) were performed on 19 women with FXTAS, 20 non-FXTAS carriers, and 26 age-matched controls. The results were compared with existing data on corresponding male carriers.

RESULTS

Women with FXTAS and non-FXTAS carriers had reduced sensory nerve action potential amplitudes. Also, there was a strong trend for reduced compound muscle action potential amplitudes in women with FXTAS, but not in non-FXTAS carriers. No significant slowing of nerve conduction velocities, prolongation of F-wave latencies, or associations with molecular measures was observed.

CONCLUSIONS

This study suggests an underlying axonal neuropathy in women with FXTAS. However, in comparison to men with FXTAS, the NCS abnormalities in women were less severe, possibly due to the effect of a normal X chromosome.

Current research, diagnosis, and treatment of fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is caused by a premutation CGG-repeat expansion in the 5'UTR of the fragile X mental retardation 1 (FMR1) gene. The classical clinical manifestations include tremor, cerebellar ataxia, cognitive decline and psychiatric disorders. Other less frequent features are peripheral neuropathy and autonomic dysfunction. Cognitive decline, a form of frontal subcortical dementia, memory loss and executive function deficits are also characteristics of this disorder. In this review, we present an expansion of recommendations for genetic testing for adults with suspected premutation disorders and provide an update of the clinical, radiological and molecular research of FXTAS, as well as the current research in the treatment for this intractable complex neurodegenerative genetic disorder.

The cognitive neuropsychological phenotype of carriers of the FMR1 premutation

The fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder affecting a subset of carriers of the FMR1 (fragile X mental retardation 1) premutation. Penetrance and expression appear to be significantly higher in males than females. Although the most obvious aspect of the phenotype is the movement disorder that gives FXTAS its name, the disorder is also accompanied by progressive cognitive impairment. In this review, we address the cognitive neuropsychological and neurophysiological phenotype for males and females with FXTAS, and for male and female unaffected carriers. Despite differences in penetrance and expression, the cognitive features of the disorder appear similar for both genders, with impairment of executive functioning, working memory, and information processing the most prominent. Deficits in these functional systems may be largely responsible for impairment on other measures, including tests of general intelligence and declarative learning. FXTAS is to a large extent a white matter disease, and the cognitive phenotypes observed are consistent with what some have described as white matter dementia, in contrast to the impaired cortical functioning more characteristic of Alzheimer's disease and related disorders. Although some degree of impaired executive functioning appears to be ubiquitous among persons with FXTAS, the data suggest that only a subset of unaffected carriers of the premutation - both female and male - demonstrate such deficits, which typically are mild. The best-studied phenotype is that of males with FXTAS. The manifestations of cognitive impairment among asymptomatic male carriers, and among women with and without FXTAS, are less well understood, but have come under increased scrutiny.

Early Detection of Fragile X Syndrome: Applications of a Novel Approach for Improved Quantitative Methylation Analysis in Venous Blood and Newborn Blood Spots

BACKGROUND

Standard fragile X syndrome (FXS) diagnostic tests that target methylation of the fragile X mental retardation 1 (FMR1) CpG island 5′ of the CGG expansion can be used to predict severity of the disease in males from birth, but not in females.

METHODS

We describe methylation specific–quantitative melt analysis (MS-QMA) that targets 10 CpG sites, with 9 within FMR1 intron 1, to screen for FXS from birth in both sexes. The novel method combines the qualitative strengths of high-resolution melt and the high-throughput, quantitative real-time PCR standard curve to provide accurate quantification of DNA methylation in a single assay. Its performance was assessed in 312 control (CGG <40), 143 premutation (PM) (CGG 56–170), 197 full mutation (FM) (CGG 200–2000), and 33 CGG size and methylation mosaic samples.

RESULTS

In male and female newborn blood spots, MS-QMA differentiated FM from control alleles, with sensitivity, specificity, and positive and negative predictive values between 92% and 100%. In venous blood of FM females between 6 and 35 years of age, MS-QMA correlated most strongly with verbal IQ impairment (P = 0.002). In the larger cohort of males and females, MS-QMA correlated with reference methods Southern blot and MALDI-TOF mass spectrometry (P < 0.05), but was not significantly correlated with age. Unmethylated alleles in high-functioning FM and PM males determined by both reference methods were also unmethylated by MS-QMA.

CONCLUSIONS

MS-QMA has an immediate application in FXS diagnostics, with a potential use of its quantitative methylation output for prognosis in both sexes.

Group I metabotropic glutamate receptor mediated dynamic immune dysfunction in children with fragile X syndrome

Background

Fragile X syndrome (FXS) is the leading cause of inheritable intellectual disability in male children, and is predominantly caused by a single gene mutation resulting in expanded trinucleotide CGG-repeats within the 5’ untranslated region of the fragile X mental retardation (FMR1) gene. Reports have suggested the presence of immune dysregulation in FXS with evidence of altered plasma cytokine levels; however, no studies have directly assessed functional cellular immune responses in children with FXS. In order to ascertain if immune dysregulation is present in children with FXS, dynamic cellular responses to immune stimulation were examined.

Methods

Peripheral blood mononuclear cells (PBMC) were from male children with FXS (n = 27) and from male aged-matched typically developing (TD) controls (n = 8). PBMC were cultured for 48 hours in media alone or with lipopolysaccharides (LPS; 1 μg/mL) to stimulate the innate immune response or with phytohemagglutinin (PHA; 8 μg/mL) to stimulate the adaptive T-cell response. Additionally, the group I mGluR agonist, DHPG, was added to cultures to ascertain the role of mGluR signaling in the immune response in subject with FXS. Supernatants were harvested and cytokine levels were assessed using Luminex multiplexing technology.

Results

Children with FXS displayed similar innate immune response following challenge with LPS alone when compared with TD controls; however, when LPS was added in the presence of a group I mGluR agonist, DHPG, increased immune response were observed in children with FXS for a number of pro-inflammatory cytokines including IL-6 (P = 0.02), and IL-12p40 (P < 0.01). Following PHA stimulation, with or without DHPG, no significant differences between subjects with FXS and TD were seen.

Conclusions

In unstimulated cultures, subjects with FXS did not display altered dynamic immune response to LPS or PHA alone; however, subjects with FXS showed an altered response to co-current stimulation of LPS and DHPG, such that subjects with FXS failed to inhibit production of pro-inflammatory cytokines, suggesting a role of group I mGluR signaling in innate immune responses in FXS.

Memantine for fragile X-associated tremor/ataxia syndrome: a randomized, double-blind, placebo-controlled trial

OBJECTIVE

Memantine, an uncompetitive N-methyl-d-aspartate receptor antagonist, is currently approved by the US Food and Drug Administration for the treatment of moderate to severe Alzheimer's disease. Anecdotal reports have suggested that memantine may improve neurologic and cognitive symptoms of individuals with the neurodegenerative disease fragile X-associated tremor/ataxia syndrome (FXTAS); however, its efficacy and safety in this population have not been assessed in a controlled trial.

METHOD

Individuals with FXTAS aged 34-80 years were enrolled in a randomized, double-blind, placebo-controlled, 1-year trial between September 2007 and August 2012. Inclusion required definite, probable, or possible FXTAS in clinical stages 1-5 according to previously published criteria. Primary outcome measures were the Behavioral Dyscontrol Scale (BDS) score and CATSYS intention tremor severity.

RESULTS

Ninety-four participants were randomized from 205 screened; of those, 43 and 45 started treatment with memantine (titrated to 10 mg twice daily) and placebo, respectively. Thirty-four participants receiving memantine and 36 receiving placebo completed the 1-year endpoint assessment (n = 70). Intention-to-treat analysis showed no improvement with respect to intention tremor severity (mean [SD] values with memantine vs placebo: 1.05 [0.73] vs 1.89 [2.19], P = .047) or BDS score (16.12 [5.43] vs 15.72 [3.93], P = .727) at follow-up. Post hoc analyses of participants with early FXTAS (stage ≤ 3), those with late FXTAS (stage > 3), and those in different age groups (≤ 65 years and > 65 years) also indicated no significant improvement. More frequent mild adverse events were observed in the placebo group, while more frequent moderate adverse events occurred in the memantine group (P = .007).

CONCLUSION

This randomized, double-blind, placebo-controlled trial of memantine for individuals with FXTAS showed no benefit compared to placebo with respect to the selected outcome measures.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00584948.

Towards an Understanding of Neuropsychiatric Manifestations in Fragile X Premutation Carriers

Fragile X-associated disorders (FXD) are a group of disorders caused by expansion of non-coding CGG repeat elements in the fragile X (FMR1) gene. One of these disorders, fragile X syndrome (FXS), is the most common heritable cause of intellectual disability, and is caused by large CGG repeat expansions (>200) resulting in silencing of the FMR1 gene. An increasingly recognized number of neuropsychiatric FXD have recently been identified that are caused by 'premutation' range expansions (55-200). These disorders are characterized by a spectrum of neuropsychiatric manifestations ranging from an increased risk of neurodevelopmental, mood and anxiety disorders to neurodegenerative phenotypes such as the fragile X-associated tremor ataxia syndrome (FXTAS). Here, we review advances in the clinical understanding of neuropsychiatric disorders in premutation carriers across the lifespan and offer guidance for the detection of such disorders by practicing psychiatrists and neurologists.

Molecular Advances Leading to Treatment Implications for Fragile X Premutation Carriers

Fragile X syndrome (FXS) is the most common single gene cause of intellectual disability and it is characterized by a CGG expansion of more than 200 repeats in the FMR1 gene, leading to methylation of the promoter and gene silencing. The fragile X premutation, characterized by a 55 to 200 CGG repeat expansion, causes health problems and developmental difficulties in some, but not all, carriers. The premutation causes primary ovarian insufficiency in approximately 20% of females, psychiatric problems (including depression and/or anxiety) in approximately 50% of carriers and a neurodegenerative disorder, the fragile X-associated tremor ataxia syndrome (FXTAS), in approximately 40% of males and 16% of females later in life. Recent clinical studies in premutation carriers have expanded the health problems that may be seen. Advances in the molecular pathogenesis of the premutation have shown significant mitochondrial dysfunction and oxidative stress in neurons which may be amenable to treatment. Here we review the clinical problems of carriers and treatment recommendations.

Reduced excitatory amino acid transporter 1 and metabotropic glutamate receptor 5 expression in the cerebellum of fragile X mental retardation gene 1 premutation carriers with fragile X-associated tremor/ataxia syndrome

A premutation (PM) expansion (55-200 CGG) in the fragile X mental retardation gene 1 causes elevated messenger RNA and reduced fragile X mental retardation gene 1 protein. Young PM carriers can develop characteristic physical features and mild cognitive disabilities. In addition, individuals with PM, particularly male carriers, are at high risk to develop fragile X-associated tremor/ataxia syndrome (FXTAS) with aging. Human postmortem FXTAS brains show extensive white matter disease in the cerebellum and the presence of intranuclear inclusions throughout the brain, although their etiologic significance is unknown. In the current work, expression levels of the metabotropic glutamate (Glu) receptor 5 and the Glu transporter excitatory amino acid transporter 1, examined by reverse transcription polymerase chain reaction and western blot analyses, were found to be reduced in the postmortem cerebellum of PM carriers with FXTAS compared with age matched controls, with higher CGG repeat number having greater reductions in both proteins. These data suggests a dysregulation of Glu signaling in PM carriers, which would likely contribute to the development and severity of FXTAS.

Advances in clinical and molecular understanding of the FMR1 premutation and fragile X-associated tremor/ataxia syndrome

Fragile X syndrome, the most common heritable form of cognitive impairment, is caused by epigenetic silencing of the fragile X (FMR1) gene owing to large expansions (>200 repeats) of a non-coding CGG-repeat element. Smaller, so-called premutation expansions (55-200 repeats) can cause a family of neurodevelopmental phenotypes (attention deficit hyperactivity disorder, autism spectrum disorder, seizure disorder) and neurodegenerative (fragile X-associated tremor/ataxia syndrome [FXTAS]) phenotypes through an entirely distinct molecular mechanism involving increased FMR1 mRNA production and toxicity. Results of basic cellular, animal, and human studies have helped to elucidate the underlying RNA toxicity mechanism, while clinical research is providing a more nuanced picture of the range of clinical manifestations. Advances of knowledge on both mechanistic and clinical fronts are driving new approaches to targeted treatment, but two important necessities are emerging: to define the extent to which the mechanisms contributing to FXTAS also contribute to other neurodegenerative and medical disorders, and to redefine FXTAS in view of its differing presentations and associated features.