Improving fragile X-associated tremor/ataxia syndrome symptoms with memantine and venlafaxine

The Role of Glutamate in Language and Language Disorders - Evidence from ERP and Pharmacologic Studies

Current models of language processing do not address mechanisms at the neurotransmitter level, nor how pharmacologic agents may improve language function(s) in seemingly disparate disorders. L-Glutamate, the primary excitatory neurotransmitter in the human brain, is extensively involved in various higher cortical functions. We postulate that the physiologic role of L-Glutamate neurotransmission extends to the regulation of language access, comprehension, and production, and that disorders in glutamatergic transmission and circuitry contribute to the pathogenesis of neurodegenerative diseases and sporadic-onset language disorders such as the aphasic stroke syndromes. We start with a review of basic science data pertaining to various glutamate receptors in the CNS and ways that they may influence the physiological processes of language access and comprehension. We then focus on the dysregulation of glutamate neurotransmission in three conditions in which language dysfunction is prominent: Alzheimer's Disease, Fragile X-associated Tremor/Ataxia Syndrome, and Aphasic Stroke Syndromes. Finally, we review the pharmacologic and electrophysiologic (event related brain potential or ERP) data pertaining to the role glutamate neurotransmission plays in language processing and disorders.

A Chinese case of fragile X-associated tremor/ataxia syndrome (FXTAS) with orthostatic tremor:case report and literature review on tremor in FXTAS

BACKGROUND

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late onset, X-linked genetic, neurodegenerative disorder caused by a "premutation (PM)" in the fragile X mental retardation 1 (FMR1) gene. Here we report a case of FXTAS from mainland of China who presented with rare orthostatic tremor. A review of tremor of FXTAS in the literature is also included.

CASE PRESENTATION

A 67-year-old right-handed farmer started with tremor of both legs 8 years ago which was present while standing but absent when sitting or lying and progressed with unsteady gait one and a half years ago. The brain MRI showed high intensity signal in the bilateral middle cerebellar peduncles (MCP) in T2-weighted and fluid-attenuated inversion recovery (FLAIR) images and gene test for premutation for FMR1 was positive with 101 CGG repeats. The patient met the the diagnosis of definite FXTAS. Clonazepam and topiramate were administered to control tremor. We reviewed the literature and identified 64 cases with detailed clinical and genetic information. Orthostatic tremor associated with FXTAS is very rare. We found 85.2% patients reported tremor,42.6% with intention tremor,36.1% with kinetic tremor,32.8% with rest tremor and 29.5% with posture tremor. 37.7% of patients who have tremor showed at least two types of tremor. There were 6 patients with isolated rest tremor. There was 2 patient with voice tremor and 6 with head tremor. We also found that 74.6% FXTAS patients had family history of FMR1 gene associated diseases including Fragile X syndrome (FXS), FXTAS or fragile X-associated primary ovarian insufficiency (FXPOI).

CONCLUSIONS

Adding our data to the available literature suggests that orthostatic tremor could be a rare initial manifestation of FXTAS and the review will increasing our understanding the phenotype of tremor in FXTAS. Family history of FMR1 gene associated diseases might be an important clue to the diagnosis.

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.

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.

Memantine Improves Attentional Processes in Fragile X-Associated Tremor/Ataxia Syndrome: Electrophysiological Evidence from a Randomized Controlled Trial

Progressive cognitive deficits are common in patients with fragile X-associated tremor/ataxia syndrome (FXTAS), with no targeted treatment yet established. In this substudy of the first randomized controlled trial for FXTAS, we examined the effects of NMDA antagonist memantine on attention and working memory. Data were analyzed for patients (24 in each arm) who completed both the primary memantine trial and two EEG recordings (at baseline and follow-up) using an auditory “oddball” task. Results demonstrated significantly improved attention/working memory performance after one year only for the memantine group. The event-related potential P2 amplitude elicited by non-targets was significantly enhanced in the treated group, indicating memantine-associated improvement in attentional processes at the stimulus identification/discrimination level. P2 amplitude increase was positively correlated with improvement on the behavioral measure of attention/working memory during target detection. Analysis also revealed that memantine treatment normalized the P2 habituation effect at the follow-up visit. These findings indicate that memantine may benefit attentional processes that represent fundamental components of executive function/dysfunction, thought to comprise the core cognitive deficit in FXTAS. The results provide evidence of target engagement of memantine, as well as therapeutically relevant information that could further the development of specific cognitive or disease-modifying therapies for FXTAS.

Fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that affects some but not all carriers of small, noncoding CGG-repeat expansions (55-200 repeats; premutation) within the fragile X gene (FMR1). Principal features of FXTAS include intention tremor, cerebellar ataxia, Parkinsonism, memory and executive function deficits, autonomic dysfunction, brain atrophy with white matter disease, and cognitive decline. Although FXTAS was originally considered to be confined to the premutation range, rare individuals with a gray zone (45-54 repeats) or an unmethylated full mutation (>200 repeats) allele have now been described, the constant feature of the disorder remaining the requirement for FMR1 expression, in contradistinction to the gene silencing mechanism of fragile X syndrome. Although transcriptional activity is required for FXTAS pathogenesis, the specific trigger(s) for FXTAS pathogenesis remains elusive, highlighting the need for more research in this area. This need is underscored by recent neuroimaging findings of changes in the central nervous system that consistently appear well before the onset of clinical symptoms, thus creating an opportunity to delay or prevent the appearance of FXTAS.

Memantine effects on verbal memory in fragile X-associated tremor/ataxia syndrome (FXTAS): a double-blind brain potential study

Older FMR1 premutation carriers may develop fragile X-associated tremor/ataxia syndrome (FXTAS), a neurodegenerative disorder manifesting cognitive deficits that often subsequently progress to dementia. To date, there is no specific treatment available for FXTAS. Studies have demonstrated the premutation-associated overactivation of glutamatergic receptors in neurons. Memantine, a NMDA receptor antagonist approved for treatment of Alzheimer's disease, thus was tested in the first placebo-controlled, double-blind, randomized clinical trial in FXTAS. Prior event-related brain potential (ERP) studies in FXTAS found reduced N400 repetition effect, a glutamate-related electrophysiological marker of semantic priming, and verbal memory processes. This substudy of the randomized clinical trial of memantine in FXTAS sought to use the N400 repetition effect to evaluate effects of chronic memantine treatment on verbal memory. Subsequent recall and recognition memory tests for the experimental stimuli were administered to characterize verbal memory. Data from 41 patients who completed the 1-year memantine trial (21 on memantine) and also completed longitudinal ERP studies were analyzed. Results showed treatment-associated benefits on both cued-recall memory and N400 repetition effect amplitude. Importantly, improvement in cued recall was positively correlated with amplitude increase of the N400 repetition effect. The placebo group, in contrast, displayed a significant reduction of the N400 repetition effect after 1 year. These results suggest that memantine treatment may have beneficial effects on verbal memory in FXTAS. Additional studies of memantine, perhaps in combination with other therapeutic agents, appear warranted, as symptomatic treatments and neuroprotective treatments are both needed for this recently recognized neurodegenerative disorder.

Emerging topics in FXTAS

This paper summarizes key emerging issues in fragile X-associated tremor/ataxia syndrome (FXTAS) as presented at the First International Conference on the FMR1 Premutation: Basic Mechanisms & Clinical Involvement in 2013.

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.

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.

Clinical neurogenetics: fragile x-associated tremor/ataxia syndrome

This article summarizes the clinical findings, genetics, pathophysiology, and treatment of fragile X-associated tremor ataxia syndrome. The disorder occurs from a CGG repeat (55-200) expansion in the fragile X mental retardation 1 gene. It manifests clinically in kinetic tremor, gait ataxia, and executive dysfunction, usually in older men who carry the genetic abnormality. The disorder has distinct radiographic and pathologic findings. Symptomatic treatment is beneficial in some patients. The inheritance is X-linked and family members may be at risk for other fragile X-associated disorders. This information is useful to neurologists, general practitioners, and geneticists.

PSYCHIATRIC DISORDERS ASSOCIATED WITH FXTAS

Carriers of the FMR1 premutation (with 55-200 CGG repeats) may present with multiple medical and psychiatric disorders. Middle-aged carriers (males more often than females) may suffer from fragile X-associated tremor/ataxia syndrome (FXTAS). FXTAS is a newly discovered neurodegenerative disease characterized by intention tremor and ataxia, along with several other neurological features. Psychiatric manifestations are common in premutation carriers of both genders and include attention deficits, anxiety, depression, irritability, impulse dyscontrol, and substance abuse or dependence. Major depressive disorder, panic disorder with or without agoraphobia, generalized anxiety disorder, social phobia, and specific phobia are among the psychiatric diagnoses often encountered in premutation carriers, including those with FXTAS. Later in the course of the illness, cognitive deficits (including dementia) may occur. In this paper, we discuss common psychiatric phenotypes in FXTAS, based on a thorough review of the literature, as well as our own research experience. Symptomatic pharmacologic treatments are available, although disease modifying agents have not yet been developed.

COGNITIVE DYSFUNCTION IN FMR1 PREMUTATION CARRIERS

Premutation carriers of the fragile X mental retardation gene (especially men) older than 50 may develop a neurodegenerative disease, the fragile X-associated tremor/ataxia syndrome (FXTAS). Carriers may present with varied cognitive impairments. Attention, working memory, declarative and procedural learning, information processing speed, and recall are among the cognitive domains affected. Executive dysfunction is a prominent deficit, which has been demonstrated mostly in men with FXTAS. In more advanced stages of FXTAS, both men and women may develop a mixed cortical-subcortical dementia, manifested by psychomotor slowing and deficits in attention, retrieval, recall, visuospatial skills, occasional apraxia, as well as overt personality changes. Studies have shown dementia rates as high as 37-42% in older men with FXTAS, although more research is needed to understand the prevalence and risk factors of dementia in women with FXTAS. Neuropsychiatric symptoms are common and reflect the dysfunction of underlying frontal-subcortical neural circuits, along with components of the cerebellar cognitive affective syndrome. These include labile or depressed mood, anxiety, disinhibition, impulsivity, and (rarely) psychotic symptoms. In this paper we review the information available to date regarding the prevalence and clinical picture of FXTAS dementia. Differential diagnosis may be difficult, given overlapping motor and non-motor signs with several other neurodegenerative diseases. Anecdotal response to cholinesterase inhibitors and memantine has been reported, while symptomatic treatments can address the neuropsychiatric manifestations of FXTAS dementia.

Fragile x-associated tremor ataxia syndrome: the expanding clinical picture, pathophysiology, epidemiology, and update on treatment

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive degenerative movement disorder characterized by kinetic tremor, cerebellar gait ataxia, parkinsonism, and cognitive decline. This disorder occurs in both males and females, frequently in families with children who have fragile X syndrome. The clinical features of this disorder, both classic and newly described, are summarized in this paper. In screening studies, fragile X mental retardation 1 (FMR1) gene premutation (55–200 CGG) expansions are most frequently seen in men with ataxia who have tested negative for spinocerebellar ataxias. Since the original description, the classic FXTAS phenotype has now been reported in females and in carriers of smaller (45–54 CGG) and larger (>200 CGG) expansions in FMR1. Premutation carriers may present with a Parkinson disease phenotype or hypotension, rather than with tremor and/or ataxia. Parkinsonism and gait ataxia may also be seen in individuals with gray zone (41–54 CGG) expansions. Studies regarding medication to treat the symptoms in FXTAS are few in number and suggest that medications targeted to specific symptoms, such as kinetic tremor or gait ataxia, may be most beneficial. Great progress has been made in regards to FXTAS research, likely given the readily available gene test and the screening of multiple family members, including parents and grandparents, of fragile X syndrome children. Expansion of genotypes and phenotypes in the disorder may suggest that a broader disease definition might be necessary in the future.

The fragile X-associated tremor ataxia syndrome (FXTAS) in Indonesia

Fragile X-associated disorders caused by the premutation of the FMR1 gene, includes the fragile X-associated tremor/ataxia syndrome (FXTAS). FXTAS affects more than 40% of premutation males over the age of 50 and 75% over the age of 80. FMR1 molecular analysis was done using PCR and confirmed by Southern Blot. Three premutation males were diagnosed FXTAS using quantification based on the standard neurological examination. Cognitive impairment was assessed using Raven and WAIS-R test. MRI was done to identify the middle cerebellar peduncle (MCP) sign, white matter disease and/or cerebral atrophy. Three cases of FXTAS are identified, of five individuals older than 50 years in one family tree two met criteria for definite FXTAS and the third with sub-clinical symptoms, although cognitive and radiological criteria are met. These cases are the first identified FXTAS cases in rural Indonesia. In addition with lack of routine medical follow-up, complications of FXTAS, such as hypertension may go unrecognized and untreated, which may further exacerbate the central nervous system (CNS) findings of FXTAS.

Preliminary study of intravenous amantadine treatment for ataxia management in patients with probable multiple system atrophy with predominant cerebellar ataxia

BACKGROUND AND PURPOSE

Multiple system atrophy with predominant cerebellar ataxia is a disabling neurologic disease. However, effective management has not yet been established. We conducted a short-term, open-label preliminary study to assess the benefits of intravenous amantadine treatment in patients with probable multiple system atrophy with predominant cerebellar ataxia.

METHODS

Twenty patients (10 male, 10 female) with probable multiple system atrophy with predominant cerebellar ataxia received 400 mg of amantadine by intravenous per day for 5 days. Ataxia severity was evaluated by the International Cooperative Ataxia Rating Scale before and after intravenous amantadine therapy and all subjects reported subjective improvement after intravenous amantadine treatment using a patient global impression scale. We analyzed the total and subscale scores by the ataxia scale and patient global impression scale.

RESULTS

The mean age was 57.4 years (range: 47-72) and the mean disease duration was 30.8 months (range: 11-79). The ataxia severity significantly decreased after intravenous amantadine therapy from 42.5 to 37.3 (p < 0.001). The mean patient global impression scale for improvement was 2.9 and there were no side effects of intravenous amantadine treatment observed. When we assessed responders, the duration of intravenous amantadine effect was more than 1 month in 4 subjects of 7 responders.

CONCLUSIONS

Our findings suggest that intravenous amantadine treatment can be a safe management option in cerebellar ataxia, although the mechanism is unclear. Thus, further double-blind, long-term studies with a larger sample size are needed.

A Quantitative Assessment of Tremor and Ataxia in Female FMR1 Premutation Carriers Using CATSYS

The fragile X-associated tremor/ataxia syndrome (FXTAS) is a relatively common cause of balance problems leading to gait disturbances in older males (40%) with the premutation. FXTAS is less common in females. We utilized the CATSYS system, a quantitative measure of movement, in 23 women with FXTAS (mean age 62.7; SD 12.3), 90 women with the premutation without FXTAS (mean age 52.9; SD 9.4), and 37 controls (mean age 56.53; SD 7.8). CATSYS distinguished differences between carriers with and without FXTAS in postural tremor, postural sway, hand coordination, and reaction time tasks. Differences were also seen between carriers without FXTAS and controls in finger tapping, reaction time, and one postural sway task. However, these differences did not persist after statistical correction for multiple comparisons. Notably, there were no differences across groups in intention tremor. This is likely due to the milder symptoms in females compared to males with FXTAS.

Motor deficits on a ladder rung task in male and female adolescent and adult CGG knock-in mice

The fragile X premutation is a tandem CGG trinucleotide repeat expansion on the FMR1 gene between 55 and 200 repeats in length. A CGG knock-in (CGG KI) mouse with CGG trinucleotide repeat lengths between 70 and 350 has been developed and used to model the histopathology and cognitive deficits reported in carriers of the fragile X premutation. Previous studies have shown that CGG KI mice show progressive deficits in processing spatial and temporal information. To characterize the motor deficits associated with the fragile X premutation, male and female CGG KI mice ranging from 2 to 16 months of age with trinucleotide repeats ranging from 72 to 240 CGG in length were tested for their ability to perform a skilled ladder rung walking test. The results demonstrate that both male and female CGG KI mice showed a greater number of foot slips as a function of increased CGG repeat length, independent of the age of the animal or general activity level.