Parkinsonism in fragile X-associated tremor/ataxia syndrome (FXTAS): Revisited

BackgroundParkinsonian features have been used as a minor diagnostic criterion for fragile X-associated tremor/ataxia syndrome (FXTAS). However, prior studies have examined parkinsonism (defined as having bradykinesia with at least rest tremor or postural instability) mostly in premutation carriers without a diagnosis of FXTAS. The current study was intended to elaborate this important aspect of the FXTAS spectrum, and to quantify the relationships between parkinsonism, FXTAS clinical staging and genetic/molecular measures.MethodsThirty eight (38) FXTAS patients and 10 age-matched normal controls underwent a detailed neurological examination that included all but one item (i.e. rigidity) of the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS).ResultsThe FXTAS patient group displayed substantially higher prevalence of parkinsonian features including body bradykinesia (57%) and rest tremor (26%), compared to the control group. Furthermore, parkinsonism was identified in 29% of FXTAS patients. Across all patients, body bradykinesia scores significantly correlated with FXTAS clinical stage, FMR1 mRNA level, and ataxic gait of cerebellar origin, while postural instability was associated with intention tremor.InterpretationParkinsonian features in FXTAS appear to be characterized as bradykinesia concurrent with cerebellar gait ataxia, postural instability accompanied by intention tremor, and frequent rest tremor, representing distinctive patterns that highlight the need for further clinical studies including genetic testing for the FMR1 premutation. The association between FMR1 mRNA level and bradykinesia implicates pathophysiological mechanisms which may link FMR1 mRNA toxicity, dopamine deficiency and parkinsonism in FXTAS.     

New clinical findings in the fragile X-associated tremor ataxia syndrome (FXTAS)

The objective of this paper was to assess the phenotypic variance in patients with the Fragile X-associated Tremor Ataxia Syndrome (FXTAS) and to further elucidate genotype–phenotype correlations in the illness. A second goal was to generate hypotheses regarding symptom progression based on careful histories in our sample that can now be tested in ongoing longitudinal studies. The variability of clinical signs and symptom progression in FXTAS complicates our understanding of its phenotype and presents a series of problems in clinical trial design. Similarly, pre-motor and non-motor symptoms have not been adequately explored to answer outstanding questions regarding genotype–phenotype associations in FXTAS. This was a cross-sectional study of FMR1 premutation carriers from known fragile X syndrome pedigrees. We report on the first 50 subjects who have completed a full neurologic evaluation and a brain MRI. Subjects were selected on the basis of motor symptoms or abnormal results (>1 SD) on a quantitative instrument designed to detect mild tremor and ataxia (CATSYS 1994). A neuropsychological battery included the WAIS-III, COWA, and WCST. Statistical analysis used ANOVA and Fisher’s exact test with p < 0.05. All FMR1 premutation carriers were men of mean age 65 ± 7 years. According to the diagnostic criteria of Jacquemont et al. (Am J Hum Genet 72(4):869–878, 2003), 21 subjects met criteria for definite FXTAS, 10 for probable, 9 for possible, and 10 were indeterminate. Duration of motor symptoms was significantly longer in the definitive group (8.6 ± 6) compared to the other groups (p < 0.01). The presentations in 40 subjects, excluding the indeterminate group, included: tremor 24, ataxia 5, memory symptoms 3, parkinsonism 2, and torticollis 1. The data suggest at least two dominant phenotypic presentations: (a) a tremor-dominant subtype in which the onset of ataxia is delayed; (b) a second in which ataxia is the dominant presentation from the outset. In both subtypes, once ataxia emerges it tends to track frontal cognitive changes (p < 0.01). The data support the view that FXTAS is a late-life neurodegenerative disorder with involvement of motor, non-motor, and cognitive systems. The results suggest at least two presentations with tremor- and ataxia-predominant phenotypes. In both, global cognitive decline appears to track ataxia. Prospective longitudinal studies are needed to validate this proposed evolution of FXTAS and its relevance to future clinical trials design.     

The primary cognitive deficit among males with fragile X-associated tremor/ataxia syndrome (FXTAS) is a dysexecutive syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder associated with a premutation trinucleotide repeat expansion in the fragile X mental retardation 1 gene. Symptoms include gait ataxia, action tremor, and cognitive impairment. The objectives of the study were to clarify the nature of the dysexecutive syndrome observed in FXTAS and to assess the contribution of executive impairment to deficits in nonexecutive cognitive functions. Compared to controls, men with FXTAS demonstrated significant executive impairment, which was found to mediate group differences in most other cognitive abilities. Asymptomatic premutation carriers performed similarly to controls on all but two measures of executive functioning. These findings suggest that the impairment of nonexecutive cognitive skills in FXTAS is in large part secondary to executive dysfunction.     

Impairment in the cognitive functioning of men with fragile X-associated tremor/ataxia syndrome (FXTAS)

Disorders associated with fragile X syndrome involve a trinucleotide (CGG) repeat expansion in the FMR1 gene. Recently, a progressive movement disorder (fragile X-associated tremor/ataxia syndrome [FXTAS]) has been identified in premutation carriers, persons with 55 to 200 CGG repeats. In addition to ataxia, action tremor, and Parkinsonism, early case reports suggested that FXTAS involves impaired cognition, but the precise nature of the impairment has not been elucidated. In this first, preliminary study of the subject, circumscribed aspects of cognitive functioning were examined in 25 men with FXTAS. Subjects' performance on the cognitive tests was compared with normative data. Scores on two measures of executive cognitive functioning showed a high prevalence of substantial impairment. Capacity for inhibition was severely affected in one-quarter of this highly educated sample; information processing speed was profoundly impaired in most subjects. Although mean verbal and performance IQ scores were not significantly different from the general population, they were quite low given the sample's educational level. Cognitive and functional impairment was greater for men with more CGG repeats, although number of repeats was not associated with age of onset of either tremor or ataxia. The results provide evidence that FXTAS involves marked impairment of executive cognitive abilities.     

Fragile X-associated tremor/ataxia syndrome (FXTAS): pathology and mechanisms

Since its discovery in 2001, our understanding of fragile X-associated tremor/ataxia syndrome (FXTAS) has undergone a remarkable transformation. Initially characterized rather narrowly as an adult-onset movement disorder, the definition of FXTAS is broadening; moreover, the disorder is now recognized as only one facet of a much broader clinical pleiotropy among children and adults who carry premutation alleles of the FMR1 gene. Furthermore, the intranuclear inclusions of FXTAS, once thought to be a CNS-specific marker of the disorder, are now known to be widely distributed in multiple non-CNS tissues; this observation fundamentally changes our concept of the disease, and may provide the basis for understanding the diverse medical problems associated with the premutation. Recent work on the pathogenic mechanisms underlying FXTAS indicates that the origins of the late-onset neurodegenerative disorder actually lie in early development, raising the likelihood that all forms of clinical involvement among premutation carriers have a common underlying mechanistic basis. There has also been great progress in our understanding of the triggering event(s) in FXTAS pathogenesis, which is now thought to involve sequestration of one or more nuclear proteins involved with microRNA biogenesis. Moreover, there is mounting evidence that mitochondrial dysregulation contributes to the decreased cell function and loss of viability, evident in mice even during the neonatal period. Taken together, these recent findings offer hope for early interventions for FXTAS, well before the onset of overt disease, and for the treatment of other forms of clinical involvement among premutation carriers.     

The fragile x-associated tremor and ataxia syndrome (FXTAS)

FXTAS (Fragile X-associated tremor and ataxia syndrome) is a late- onset neurodegenerative disorder affecting mainly men, over 50 years of age, who are carriers of the FMR1 gene premutation. The full mutation of this gene causes the fragile X syndrome (FXS), the most common cause of inherited mental retardation. Individuals affected by FXTAS generally present intention tremor and gait ataxia that might be associated to specific radiological and/or neuropathological signs. Other features commonly observed are parkinsonism, cognitive decline, peripheral neuropathy and autonomic dysfunction. Nearly a decade after its clinical characterization, FXTAS is poorly recognized in Brazil. Here we present a review of the current knowledge on the clinical, genetic and diagnostic aspects of the disease.     

Intrafamilial variability in fragile X-associated tremor/ataxia syndrome.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive adult-onset tremor/ataxia syndrome caused by premutations in the FMR1 gene. In cranial MRI, the most characteristic findings are bilateral T2 hyperintense lesions within the middle cerebellar peduncles. Here we present a sibpair of two affected brothers presenting with very different symptoms (typical FXTAS versus essential tremor-like), disease progression, and MRI findings, illustrating broad intrafamilial variability of FXTAS. Also, their family history suggests further evidence of possible manifestation of FXTAS in women.     

Expanding the phenotype of fragile X-associated tremor/ataxia syndrome: a new female case.

We report an original case of fragile X‐associated tremor/ataxia syndrome in a female carrier, who had been misdiagnosed for years because of unusual features mimicking other movement or cerebrovascular disorders. She exhibited features that have not been previously described, including voice and head tremor as well as spasmodic laryngeal dystonia. Brain MRI showed widespread leukoencephalopathy reminiscent of vascular encephalopathy, exemplifying the diversity of MRI abnormalities that could be associated with the condition. © 2007 Movement Disorder Society     

Symptomatic treatment in the fragile X-associated tremor/ataxia syndrome.

There is no established treatment for the neurological features of the recently discovered fragile X-associated tremor/ataxia syndrome (FXTAS). Fifty-six patients with FXTAS completed a questionnaire to determine whether any medications had been effective for neurological symptoms. Of 11 subjects with definite FXTAS, 8 (70%) were on medications for their neurological symptoms, whereas most subjects with possible or probable FXTAS, 31 (70%) of 45 subjects, were not on medications. Although no therapy was uniformly effective for intention tremor, ataxia, Parkinsonism, memory loss, or anxiety, some subjects with intention tremor or Parkinsonism reported improvement with medications frequently used in other movement disorders. Overall, all 22 subjects on medications reported improvement in one or more symptoms. Lack of insight, recall bias, and cognitive impairment may have resulted in an underestimation of the beneficial effect of medical therapy. This study suggests that patients with FXTAS can derive improvement from medication treatment for some of their symptoms.     

Impairment of executive cognitive functioning in males with fragile X-associated tremor/ataxia syndrome.

The fragile X-associated tremor/ataxia syndrome (FXTAS) is a recently identified phenotype associated with trinucleotide repeat expansions in the premutation range of the fragile X mental retardation 1 (FMR1) gene. In addition to progressive gait ataxia, action tremor, peripheral neuropathy, and parkinsonism, FXTAS involves impaired cognition. Our preliminary research suggests that executive cognitive functioning (ECF) is especially affected. In this study, a brief neuropsychological exam was administered to 33 men with FXTAS and 27 healthy controls. Compared with controls, individuals with FXTAS showed statistically significant impairments on measures from the Wechsler Adult Intelligence Scale, third edition (WAIS-III; verbal IQ, performance [nonverbal] IQ, verbal comprehension, perceptual organization, and processing speed). FXTAS subjects scored significantly lower on three of four measures of ECF and on two tests of information processing speed. The results provide evidence that FXTAS involves impairment of general intellectual functioning, with marked impairment of executive cognitive abilities. The pattern of cognitive performance is somewhat similar to that observed in the frontal variant of frontotemporal dementia and several of the spinocerebellar ataxias, but differs from the deficits observed in dementia of the Alzheimer type.     

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

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

Mouse models of the fragile X premutation and fragile X-associated tremor/ataxia syndrome

Carriers of the fragile X premutation (FPM) have CGG trinucleotide repeat expansions of between 55 and 200 in the 5′-UTR of FMR1, compared to a CGG repeat length of between 5 and 54 for the general population. Carriers were once thought to be without symptoms, but it is now recognized that they can develop a variety of early neurological symptoms as well as being at risk for developing the late onset neurodegenerative disorder fragile X-associated tremor/ataxia syndrome (FXTAS). Several mouse models have contributed to our understanding of FPM and FXTAS, and findings from studies using these models are summarized here. This review also discusses how this information is improving our understanding of the molecular and cellular abnormalities that contribute to neurobehavioral features seen in some FPM carriers and in patients with FXTAS. Mouse models show much of the pathology seen in FPM carriers and in individuals with FXTAS, including the presence of elevated levels of Fmr1 mRNA, decreased levels of fragile X mental retardation protein, and ubiquitin-positive intranuclear inclusions. Abnormalities in dendritic spine morphology in several brain regions are associated with neurocognitive deficits in spatial and temporal memory processes, impaired motor performance, and altered anxiety. In vitro studies have identified altered dendritic and synaptic architecture associated with abnormal Ca²⁺ dynamics and electrical network activity. FPM mice have been particularly useful in understanding the roles of Fmr1 mRNA, fragile X mental retardation protein, and translation of a potentially toxic polyglycine peptide in pathology. Finally, the potential for using these and emerging mouse models for preclinical development of therapies to improve neurological function in FXTAS is considered.     

Neuropathology of a case of fragile X-associated tremor ataxia syndrome without tremor

Fragile X-associated tremor ataxia syndrome (FXTAS) is a neurodegenerative disorder caused by a CGG trinucleotide expansion from 55 to 200 repeats in the non-coding region of the fragile X mental retardation 1 (FMR1) gene (FMR1). Clinical features include cognitive decline, progressive tremor, and gait ataxia. Neuropathologically, FXTAS shows white matter changes, hippocampal and cerebellar involvement, and p62-positive eosinophilic intranuclear inclusions in astrocytes and neurons. Here, we document the neuropathological findings from a subject who developed cognitive impairment but not tremor and was proved to have genetically confirmed FMR1 premutation. Microscopically, typical p62-postive intranuclear inclusions were present in all the regions examined. Neocortical regions demonstrated gliosis of layer I and mild degree of neuronal loss and atrophy across the other layers. The molecular, Purkinje's cell, and granule cell layers of the cerebellar folia demonstrated mild gliosis, and cerebellar white matter was mildly affected. Aside from p62-positive inclusions, the hippocampus was spared. Arteries in the deep white matter often showed changes consistent with moderate small vessel disease (SVD). Reactive gliosis and severe SVD were features of basal ganglia. Florid reactive astrocytosis was found in the white matter of all regions. Axonal loss and features of axonal damage were found in the white matter of the centrum semiovale. Microglial activation was widespread and evenly seen in both the white matter and grey matter, although the grey matter appeared more severely affected. Pathology associated with Alzheimer's disease was limited. Similarly, no abnormal accumulations of α-synuclein were present. We postulate that age at death and disease duration may play a role in the extent of the pathological features associated with FXTAS. The present results suggest that immunohistochemical staining for p62 can help with the diagnosis of cases with atypical phenotype. In addition, it is likely that the cognitive impairment observed was a result of white matter changes.