Impairment in motor reprogramming in Friedreich ataxia reflecting possible cerebellar dysfunction

Neuropsychiatric symptoms in spinocerebellar ataxias and Friedreich ataxia

Apart from its role in motor coordination, the importance of the cerebellum in cognitive and affective processes has been recognized in the past few decades. Spinocerebellar ataxias (SCA) and Friedreich ataxia (FRDA) are rare neurodegenerative diseases of the cerebellum presenting mainly with a progressive loss of gait and limb coordination, dysarthria, and other motor disturbances, but also a range of cognitive and neuropsychiatric symptoms. This narrative review summarizes the current knowledge on neuropsychiatric impairment in SCA and FRDA. We discuss the prevalence, clinical features and treatment approaches in the most commonly reported domains of depression, anxiety, apathy, agitation and impulse dyscontrol, and psychosis. Since these symptoms have a considerable impact on patients' quality of life, we argue that further research is mandated to improve the detection and treatment options of neuropsychiatric co-morbidities in ataxia patients.

The cognitive profile of Friedreich ataxia: a systematic review and meta-analysis

BACKGROUND

Study the cognitive profile of individuals with Friedreich ataxia (FRDA) and seek evidence for correlations between clinical, genetic and imaging characteristics and neuropsychological impairments.

METHODS

Based on PRISMA guidelines, a meta-analysis was realized using the Pubmed and Scopus databases to identify studies (1950-2021) reporting neuropsychological test results in genetically confirmed FRDA and control participants in at least one of the following cognitive domains: attention/executive, language, memory and visuo-spatial functions as well as emotion. Studies using identical outcomes in a minimum of two studies were pooled. Pooled effect sizes were calculated with Cohen's d.

RESULTS

Eighteen studies were included. Individuals with FRDA displayed significantly lower performance than individuals without FRDA in most language, attention, executive function, memory visuospatial function, emotion regulation and social cognitive tasks. Among the included studies, thirteen studies examined the relationship between neuropsychological test results and clinical parameters and reported significant association with disease severity and six studies reviewed the relationship between neuroimaging measures and cognitive performance and mainly reported links between reduced cognitive performance and changes in cerebellar structure.

CONCLUSIONS

Individuals with FRDA display significantly lower performances in many cognitive domains compared to control participants. The spectrum of the cognitive profile alterations in FRDA and its correlation with disease severity and cerebellar structural parameters suggest a cerebellar role in the pathophysiology of FRDA cognitive impairments.

Longitudinal investigation of brain activation during motor tasks in Friedreich ataxia: 24-month data from IMAGE-FRDA

Friedreich ataxia (FRDA) is a progressive autosomal recessive disease. While motor dysfunction is the primary neurological hallmark, little is known about the underlying neurobiological changes associated with motor deficits over the course of disease. We investigated the hypothesis that progressive functional changes in both the cerebellum and cerebrum are related to longitudinal changes in performance on complex motor tasks in individuals with FRDA. Twenty-two individuals with FRDA and 28 controls participated over 24 months. The longitudinal investigation included finger tapping tasks with different levels of complexity (i.e., visually cued, multi-finger; self-paced, single finger), performed in conjunction with fMRI acquisitions, to interrogate changes in the neurobiology of motor and attentional brain networks including the cerebellum and cerebrum. We demonstrated evidence for significant longitudinal decreased cerebral fMRI activity over time in individuals with FRDA, relative to controls, during an attentionally-demanding motor task (visually cued tapping of multiple fingers) in six cerebral regions: right and left superior frontal gyri, right superior temporal gyrus, right primary somatosensory area, right anterior cingulate cortex, and right medial frontal gyrus. Importantly, longitudinal decreased activity was associated with more severe disease status at baseline, higher GAA1 repeat length and earlier age of onset. These findings suggest a dynamic pattern of neuronal activity in motor, attention and executive control networks over time in individuals with FRDA, which is associated with increased disease severity at baseline, increased GAA1 repeat length and earlier age at onset.

Neuro-Ophthalmological Findings in Friedreich's Ataxia

Friedreich ataxia (FRDA) is a progressive neurodegenerative disease caused by a severe autosomal recessive genetic disorder of the central nervous (CNS) and peripheral nervous system (PNS), affecting children and young adults. Its onset is before 25 years of age, with mean ages of onset and death between 11 and 38 years, respectively. The incidence is 1 in 30,000–50,000 persons. It is caused, in 97% of cases, by a homozygous guanine-adenine-adenine (GAA) trinucleotide mutation in the first intron of the frataxin (FXN) gene on chromosome 9 (9q13–q1.1). The mutation of this gene causes a deficiency of frataxin, which induces an altered inflow of iron into the mitochondria, increasing the nervous system’s vulnerability to oxidative stress. The main clinical signs include spinocerebellar ataxia with sensory loss and disappearance of deep tendon reflexes, cerebellar dysarthria, cardiomyopathy, and scoliosis. Diabetes, hearing loss, and pes cavus may also occur, and although most patients with FRDA do not present with symptomatic visual impairment, 73% present with clinical neuro-ophthalmological alterations such as optic atrophy and altered eye movement, among others. This review provides a brief overview of the main aspects of FRDA and then focuses on the ocular involvement of this pathology and the possible use of retinal biomarkers.

Longitudinal Study of Cognitive Functioning in Friedreich's Ataxia

OBJECTIVE

Friedreich's ataxia (FRDA) is the most common hereditary ataxia. It is a neurodegenerative disorder, characterized by progressive ataxia. FRDA is also associated with cognitive impairments. To date, the evolution of cognitive functioning is unknown. Our aim was to investigate the changes in the cognitive functioning of FRDA patients over an average eight-year timeframe. In addition, we aimed to study the relationship between cognitive changes and clinical variables.

METHODS

Twenty-nine FRDA patients who had been part of the sample of a previous study participated in the present study. The mean average time between the two assessments was 8.24 years. The participants completed an extensive battery of neuropsychological tests chosen to examine cognitive functioning in various cognitive domains: processing speed, attention, working memory, executive functions, verbal and visual memory, visuoperceptive and visuospatial skills, visuoconstructive functions and language.

RESULTS

At follow-up, cerebellar symptoms had worsened, and patients presented greater disability. Differences between baseline and follow-up were observed in motor and cognitive reaction times, several trials of the Stroop test, semantic fluency, and block designs. No other cognitive changes were observed. Deterioration in simple cognitive reactions times and block designs performance correlated with the progression of cerebellar symptoms.

CONCLUSIONS

Our study has demonstrated for the first time that patients with FRDA experience a significant decline over time in several cognitive domains. Specifically, after an eight-year period, FRDA patients worsened in processing speed, fluency, and visuoconstructive skills. This progression is unlikely to be due to greater motor or speech impairment.

Emotion Recognition and Psychological Comorbidity in Friedreich's Ataxia

Friedreich's ataxia (FRDA) is an autosomal recessive disease presenting with ataxia, corticospinal signs, peripheral neuropathy, and cardiac abnormalities. Little effort has been made to understand the psychological and emotional burden of the disease. The aim of our study was to measure patients' ability to recognize emotions using visual and non-verbal auditory hints, and to correlate this ability with psychological, neuropsychological, and neurological variables. We included 20 patients with FRDA, and 20 age, sex, and education matched healthy controls (HC). We measured emotion recognition using the Geneva Emotion Recognition Test (GERT). Neuropsychological status was assessed measuring memory, executive functions, and prosopagnosia. Psychological tests were Patient Health Questionnaire-9 (PHQ-9), State Trait Anxiety Inventory-state/-trait (STAI-S/-T), and Structured Clinical Interview for DSM Disorders II. FRDA patients scored worse at the global assessment and showed impaired immediate visuospatial memory and executive functions. Patients presented lower STAI-S scores, and similar scores at the STAI-T, and PHQ-9 as compared to HC. Three patients were identified with personality disorders. Emotion recognition was impaired in FRDA with 29% reduction at the total GERT score (95% CI - 44.8%, - 12.6%; p < 0.001; Cohen's d = 1.2). Variables associated with poor GERT scores were the 10/36 spatial recall test, the Ray Auditory Verbal Learning Test, the Montreal Cognitive Assessment, and the STAI-T (R² = 0.906; p < 0.001). FRDA patients have impaired emotion recognition that may be secondary to neuropsychological impairment. Depression and anxiety were not higher in FRDA as compared to HC and should not be considered as part of the disease.

Depressive symptoms in Friedreich ataxia

Background/Objective: Almost no attention has been paid to depression in Friedreich ataxia (FRDA), a highly disabling cerebellar degenerative disease. Our aim was to study the presence and the profile of depressive symptoms in FRDA and their relationship with demographic-disease variables and cognitive processing speed. Method: The study groups consisted of 57 patients with a diagnosis of FRDA. The Beck Depression Inventory-II was used to assess symptoms of depression. Speed of information processing was measured with a Choice Reaction time task. Results: The mean BDI score for patients was significantly higher than the mean score in the general population. Twenty one percent of participants scored in the moderate/severe range. A Cognitive-Affective score and a Somatic-Motivational score was calculated for each patient. Patients’ scores in both dimensions were significantly higher than the scores in the general population. Demographic and disease variables were not related with symptoms of depression, except for severity of ataxia. Depressive symptoms predict cognitive reaction times. The greater proportion of variance was explained by the Cognitive-Affective dimension. Conclusions: Our data show that both somatic-motivational and cognitive affective symptoms of depression are frequent in individuals with FRDA. In addition, depressive symptoms may influence cognition, especially, the cognitive and affective symptoms.

Measuring Inhibition and Cognitive Flexibility in Friedreich Ataxia

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder with subtle impact on cognition. Inhibitory processes and cognitive flexibility were examined in FRDA by assessing the ability to suppress a predictable verbal response. We administered the Hayling Sentence Completion Test (HSCT), the Trail Making Test, and the Stroop Test to 43 individuals with FRDA and 42 gender- and age-matched control participants. There were no significant group differences in performance on the Stroop or Trail Making Test whereas significant impairment in cognitive flexibility including the ability to predict and inhibit a pre-potent response as measured in the HSCT was evident in individuals with FRDA. These deficits did not correlate with clinical characteristics of FRDA (age of disease onset, disease duration, number of guanine-adenine-adenine repeats on the shorter or larger FXN allele, or Friedreich Ataxia Rating Scale score), suggesting that such impairment may not be related to the disease process in a straightforward way. The observed specific impairment of inhibition and predictive capacity in individuals with FRDA on the HSCT task, in the absence of impairment in associated executive functions, supports cerebellar dysfunction in conjunction with disturbance to cortico-thalamo-cerebellar connectivity, perhaps via inability to access frontal areas necessary for successful task completion.

Cerebral compensation during motor function in Friedreich ataxia: The IMAGE-FRDA study

BACKGROUND

Friedreich ataxia is characterized by progressive motor incoordination that is linked to peripheral, spinal, and cerebellar neuropathology. Cerebral abnormalities are also reported in Friedreich ataxia, but their role in disease expression remains unclear.

METHODS

In this cross-sectional functional magnetic resonance imaging study, 25 individuals with Friedreich ataxia and 33 healthy controls performed simple (self-paced single-finger) and complex (visually cued multifinger) tapping tasks to respectively gauge basic and attentionally demanding motor behavior. For each task, whole brain functional activations were compared between groups and correlated with disease severity and offline measures of motor dexterity.

RESULTS

During simple finger tapping, cerebral hyperactivation in individuals with Friedreich ataxia at the lower end of clinical severity and cerebral hypoactivation in those more severely affected was observed in premotor/ventral attention brain regions, including the supplementary motor area and anterior insula. Greater activation in this network correlated with greater offline finger tapping precision. Complex, attentionally demanding finger tapping was also associated with cerebral hyperactivation, but in this case within dorsolateral prefrontal regions of the executive control network and superior parietal regions of the dorsal attention system. Greater offline motor precision was associated with less activation in the dorsal attention network.

DISCUSSION

Compensatory activity is evident in the cerebral cortex in individuals with Friedreich ataxia. Early compensation followed by later decline in premotor/ventral attention systems demonstrates capacity-limited neural reserve, while the additional engagement of higher order brain networks is indicative of compensatory task strategies. Network-level changes in cerebral brain function thus potentially serve to mitigate the impact of motor impairments in Friedreich ataxia. © 2017 International Parkinson and Movement Disorder Society.

Fronto-cerebellar dysfunction and dysconnectivity underlying cognition in friedreich ataxia: The IMAGE-FRDA study

Friedreich ataxia (FRDA) is a progressive neurodegenerative disorder defined by pathology within the cerebellum and spinal tracts. Although FRDA is most readily linked to motor and sensory dysfunctions, reported impairments in working memory and executive functions indicate that abnormalities may also extend to associations regions of the cerebral cortex and/or cerebello-cerebral interactions. To test this hypothesis, 29 individuals with genetically confirmed FRDA and 34 healthy controls performed a verbal n-back working memory task while undergoing functional magnetic resonance imaging. No significant group differences were evident in task performance. However, individuals with FRDA had deficits in brain activations both in the lateral cerebellar hemispheres, principally encompassing lobule VI, and the prefrontal cortex, including regions of the anterior insular and rostrolateral prefrontal cortices. Functional connectivity between these brain regions was also impaired, supporting a putative link between primary cerebellar dysfunction and subsequent cerebral abnormalities. Disease severity and genetic markers of disease liability were correlated specifically with cerebellar dysfunction, while correlations between behavioural performance and both cerebral activations and cerebello-cerebral connectivity were observed in controls, but not in the FRDA cohort. Taken together, these findings support a diaschisis model of brain dysfunction, whereby primary disease effects in the cerebellum result in functional changes in downstream fronto-cerebellar networks. These fronto-cerebellar disturbances provide a putative biological basis for the nonmotor symptoms observed in FRDA, and reflect the consequence of localized cerebellar pathology to distributed brain function underlying higher-order cognition.

Cognitive deficits in Friedreich ataxia correlate with micro-structural changes in dentatorubral tract

Atrophy of the dentate nucleus is one of the major neuropathological changes in Friedreich ataxia (FRDA). Neuroimaging studies demonstrated white matter (WM) degeneration in FRDA. In this study, we used advanced tractography techniques to quantitatively measure WM changes in the dentato-thalamic and dentato-rubral tracts, and correlated these changes with cognitive profiles of FRDA. We also analysed diffusivity changes of the thalamo-cortical tract to assess whether neurological degeneration of WM extends beyond the primary site of involvement in FRDA. Twelve genetically proven individuals with FRDA and 14 controls were recruited. Sixty directions diffusion tensor images were acquired. The WM bundles from the dentate nucleus were estimated using a constrained spherical deconvolution method and the diffusivity characteristics measured. The Simon task was used to assess cognitive profile of FRDA. The dentato-rubral, dentato-thalamic and thalamo-cortical tracts manifested significantly lower fractional anisotropy, higher mean diffusivity and increased radial diffusivity in FRDA compared with controls. There was no difference in axial diffusivity between the two groups. The mean and radial diffusivity of the dentato-rubral tract was positively correlated with choice reaction time, congruent reaction time, incongruent reaction time and Simon effect reaction time and negatively with the larger GAA repeat. Significant changes in diffusivity characteristics were observed in the dentato-thalamic and thalamo-cortical tracts, suggesting extensive WM degeneration and affected WM structures in FRDA. Correlation of WM changes in the dentato-rubral tract with the cognitive assessment suggested that this tract is an important contributor to cognitive disturbances in FRDA.

Functional and usability assessment of a robotic exoskeleton arm to support activities of daily life

An assistive device for upper limb support was developed and evaluated in terms of usability, user satisfaction and motor performance on six end-users affected by neuro-motor disorders (three spinal cord injury; one multiple sclerosis; two Friedreich's ataxia). The system consisted of a lightweight 3-degrees-of-freedom robotic exoskeleton arm for weight relief, equipped with electromagnetic brakes. Users could autonomously control the brakes using a USB-button or residual electromyogram activations. The system functionally supported all of the potential users in performing reaching and drinking tasks. For three of them, time, smoothness, straightness and repeatability were also comparable to healthy subjects. An overall high level of usability (system usability score, median value of 90/100) and user satisfaction (Tele-healthcare Satisfaction Questionnaire - Wearable Technology, median value of 104/120) were obtained for all subjects.

Cell and gene therapy for Friedreich ataxia: progress to date

Neurodegenerative disorders such as Friedreich ataxia (FRDA) present significant challenges in developing effective therapeutic intervention. Current treatments aim to manage symptoms and thus improve quality of life, but none can cure, nor are proven to slow, the neurodegeneration inherent to this disease. The primary clinical features of FRDA include progressive ataxia and shortened life span, with complications of cardiomyopathy being the major cause of death. FRDA is most commonly caused by an expanded GAA trinucleotide repeat in the first intron of FXN that leads to reduced levels of frataxin, a mitochondrial protein important for iron metabolism. The GAA expansion in FRDA does not alter the coding sequence of FXN. It results in reduced production of structurally normal frataxin, and hence any increase in protein level is expected to be therapeutically beneficial. Recently, there has been increased interest in developing novel therapeutic applications like cell and/or gene therapies, and these cutting-edge applications could provide effective treatment options for FRDA. Importantly, since individuals with FRDA produce frataxin at low levels, increased expression should not elicit an immune response. Here we review the advances to date and highlight the future potential for cell and gene therapy to treat this debilitating disease.

Saccade reprogramming in Friedreich ataxia reveals impairments in the cognitive control of saccadic eye movement

Although cerebellar dysfunction has known effects on motor function in Friedreich ataxia (FRDA), it remains unclear the extent to which the reprogramming of eye movements (saccades) and inhibition of well-learned automatic responses are similarly compromised in affected individuals. Here we examined saccade reprogramming to assess the ability of people with FRDA to respond toward unexpected changes in either the amplitude or direction of an "oddball" target. Thirteen individuals with genetically confirmed FRDA and 12 age-matched controls participated in the study. The saccade reprogramming paradigm was used to examine the effect of an unpredictable "oddball" target on saccade latencies and accuracy when compared to a well-learned sequence of reciprocating movements. Horizontal eye movements were recorded using a scleral search coil eye tracking technique. The results showed a proportionally greater increase in latencies for reprogrammed saccades toward an oddball-direction target in the FRDA group when compared to controls. The FRDA group were also less accurate in primary saccade gain (i.e. ratio of saccade amplitude to target amplitude) when reprogramming saccades toward an unexpected change in direction. No significant group differences were found on any of the oddball-amplitude targets. Significant correlations were revealed between latency and disease severity as measured by the Friedreich Ataxia Rating Scale. These findings provide further support to the view that cognitive changes in FRDA may arise from disruption of cerebellar connections to cortical structures.

Clinical features of Friedreich's ataxia: classical and atypical phenotypes

One hundred and fifty years since Nikolaus Friedreich's first description of the degenerative ataxic syndrome which bears his name, his description remains at the core of the classical clinical phenotype of gait and limb ataxia, poor balance and coordination, leg weakness, sensory loss, areflexia, impaired walking, dysarthria, dysphagia, eye movement abnormalities, scoliosis, foot deformities, cardiomyopathy and diabetes. Onset is typically around puberty with slow progression and shortened life-span often related to cardiac complications. Inheritance is autosomal recessive with the vast majority of cases showing an unstable intronic GAA expansion in both alleles of the frataxin gene on chromosome 9q13. A small number of cases are caused by a compound heterozygous expansion with a point mutation or deletion. Understanding of the underlying molecular biology has enabled identification of atypical phenotypes with late onset, or atypical features such as retained reflexes. Late-onset cases tend to have slower progression and are associated with smaller GAA expansions. Early-onset cases tend to have more rapid progression and a higher frequency of non-neurological features such as diabetes, cardiomyopathy, scoliosis and pes cavus. Compound heterozygotes, including those with large deletions, often have atypical features. In this paper, we review the classical and atypical clinical phenotypes of Friedreich's ataxia.

Cognition in Friedreich ataxia

Friedreich ataxia (FRDA) is the most frequent of the inherited ataxias. However, very few studies have examined the cognitive status of patients with genetically defined FRDA. Our aim was to study cognitive performance of FRDA patients taking into account the motor problems characteristic of this clinical population. Thirty-six FRDA patients were administered a comprehensive neuropsychological battery measuring multiple domains: processing speed, attention, working memory, executive functions, verbal and visual memory, visuoperceptive and visuospatial skills, visuoconstructive functions, and language. Thirty-one gender, age, years of education, and estimated IQ-matched healthy participants served as control subjects. All participants were native Spanish speakers. Patients showed decreased motor and mental speed, problems in conceptual thinking, a diminished verbal fluency, deficits in acquisition of verbal information and use of semantic strategies in retrieval, visuoperceptive and visuoconstructive problems, and poor action naming. Scores on the depression inventory were significantly higher in patients than controls, but depression did not account for group differences in cognitive performance. The observed pattern of neuropsychological impairment is indicative of executive problems and parieto-temporal dysfunction. Neuropathological and neuroimaging studies with FRDA patients have reported only mild anomalies in cerebral hemispheres. Thus, cognitive impairment in FRDA is probably caused by the interruption of the cerebro-cerebellar circuits that have been proposed as the anatomical substrate of the cerebellar involvement in cognition.

Cerebello-cerebral connectivity deficits in Friedreich ataxia

Brain pathology in Friedreich ataxia is characterized by progressive degeneration of nervous tissue in the brainstem, cerebellum and cerebellar peduncles. Evidence of cerebral involvement is however equivocal. This brain imaging study investigates cerebello-cerebral white matter connectivity in Friedreich ataxia with diffusion MRI and tractography performed in 13 individuals homozygous for a GAA expansion in intron one of the frataxin gene and 14 age- and gender-matched control participants. New evidence is presented for disrupted cerebello-cerebral connectivity in the disease, leading to secondary effects in distant cortical and subcortical regions. Remote regions affected by primary cerebellar and brainstem pathology include the supplementary motor area, cingulate cortex, frontal cortices, putamen and other subcortical nuclei. The connectivity disruptions identified provide an explanation for some of the non-ataxic symptoms observed in the disease and support the notion of reverse cerebellar diaschisis. This is the first study to comprehensively map white matter connectivity disruptions in Friedreich ataxia using tractography, connectomic techniques and super-resolution track density imaging.

Excessive motor overflow reveals abnormal inter-hemispheric connectivity in Friedreich ataxia

This study sought to characterise force variability and motor overflow in 12 individuals with Friedreich ataxia (FRDA) and 12 age- and gender-matched controls. Participants performed a finger-pressing task by exerting 30 and 70 % of their maximum finger force using the index finger of the right and left hand. Control of force production was measured as force variability, while any involuntary movements occurring on the finger of the other, passive hand, was measured as motor overflow. Significantly greater force variability in individuals with FRDA compared with controls is indicative of cortico-cerebellar disruption affecting motor control. Meanwhile, significantly greater motor overflow in this group provides the first evidence of possible abnormal inter-hemispheric activity that may be attributable to asymmetrical neuronal loss in the dentate nucleus. Overall, this study demonstrated a differential engagement in the underlying default processes of the motor system in FRDA.

Clinical features of Friedreich ataxia

Friedreich ataxia, the most common hereditary ataxia, affects approximately 1 per 29,000 white individuals. In about 98% of these individuals, it is due to homozygosity for a GAA trinucleotide repeat expansion in intron 1 of FXN; in the other 2%, it is due to compound heterozygosity for a GAA expansion and point mutation or deletion. The condition affects multiple sites in the central and peripheral nervous system as well as a number of other organ systems, resulting in multiple signs and symptoms. Onset of this autosomal recessive condition is usually in the first 2 decades of life. Major clinical features include progressive ataxia, absent lower limb reflexes, upgoing plantar responses, and peripheral sensory neuropathy. The main nonneurological sites of morbidity are the heart, resulting in cardiomyopathy, and the pancreas, resulting in diabetes mellitus. In this review, we provide an overview of the clinical features of Friedreich ataxia and discuss differential diagnoses.

Unanswered questions in Friedreich ataxia

During the past 15 years, the pace of research advancement in Friedreich ataxia has been rapid. The abnormal gene has been discovered and its gene product characterized, leading to the development of new evidence-based therapies. Still, various unsettled issues remain that affect clinical trials. These include the level of frataxin deficiency needed to cause disease, the mechanism by which frataxin-deficient mitochondrial dysfunction leads to symptomatology, and the reason selected cells are most affected in Friedreich ataxia. In this review, we summarize these questions and propose testable hypotheses for their resolution.

Utilisation of advance motor information is impaired in Friedreich ataxia

Friedreich ataxia (FRDA) is the most common of the genetically inherited ataxias. We sought to examine motor planning ability in 13 individuals with FRDA and 13 age- and sex-matched control participants using two experimental paradigms that examined the ability to incorporate different levels of advance information to plan sequential movements. Individuals with FRDA demonstrated a differential pattern of motor response to advance information and were significantly disadvantaged by conditions requiring initiation of movement without a direct visual cue. There was also a significant negative correlation with age of disease onset and differing levels of advance information, suggesting an impact of FRDA on the development of motor cognition, independent of the effect of disease duration. We suggest that deficits are due to cerebellar impairment disrupting cerebro-ponto-cerebello-thalamo-cerebral loops (and thus cortical function), direct primary cortical pathology or a possible combination of the two.

Decreased functional brain activation in Friedreich ataxia using the Simon effect task

The present study applied the Simon effect task to examine the pattern of functional brain reorganization in individuals with Friedreich ataxia (FRDA), using functional magnetic resonance imaging (fMRI). Thirteen individuals with FRDA and 14 age and sex matched controls participated, and were required to respond to either congruent or incongruent arrow stimuli, presented either to the left or right of a screen, via laterally-located button press responses. Although the Simon effect (incongruent minus congruent stimuli) showed common regions of activation in both groups, including the superior and middle prefrontal cortices, insulae, superior and inferior parietal lobules (LPs, LPi), occipital cortex and cerebellum, there was reduced functional activation across a range of brain regions (cortical, subcortical and cerebellar) in individuals with FRDA. The greater Simon effect behaviourally in individuals with FRDA, compared with controls, together with concomitant reductions in functional brain activation and reduced functional connectivity between cortical and sub-cortical regions, implies a likely disruption of cortico-cerebellar loops and ineffective engagement of cognitive/attention regions required for response suppression.

Characterising the neuropathology and neurobehavioural phenotype in Friedreich ataxia: a systematic review

Friedreich ataxia (FRDA), the most common of the hereditary ataxias, is an autosomal recessive, multisystem disorder characterised by progressive ataxia, sensory symptoms, weakness, scoliosis and cardiomyopathy. FRDA is caused by a GAA expansion in intron one of the FXN gene, leading to reduced levels of the encoded protein frataxin, which is thought to regulate cellular iron homeostasis. The cerebellar and spinocerebellar dysfunction seen in FRDA has known effects on motor function; however until recently slowed information processing has been the main feature consistently reported by the limited studies addressing cognitive function in FRDA. This chapter will systematically review the current literature regarding the neuropathological and neurobehavioural phenotype associated with FRDA. It will evaluate more recent evidence adopting systematic experimental methodologies that postulate that the neurobehavioural phenotype associated with FRDA is likely to involve impairment in cerebello-cortico connectivity.

A novel deletion-insertion mutation identified in exon 3 of FXN in two siblings with a severe Friedreich ataxia phenotype

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disease most commonly caused by a GAA trinucleotide repeat expansion in the first intron of FXN, which reduces expression of the mitochondrial protein frataxin. Approximately 98% of individuals with FRDA are homozygous for GAA expansions, with the remaining 2% compound heterozygotes for a GAA expansion and a point mutation within FXN. Two siblings with early onset of symptoms experienced rapid loss of ambulation by 8 and 10 years. Diagnostic testing for FRDA demonstrated one GAA repeat expansion of 1010 repeats and one non-expanded allele. Sequencing all five exons of FXN identified a novel deletion-insertion mutation in exon 3 (c.371_376del6ins15), which results in a modified frataxin protein sequence at amino acid positions 124-127. Specifically, the amino acid sequence changes from DVSF to VHLEDT, increasing frataxin from 211 residues to 214. Using the known structure of human frataxin, a theoretical 3D model of the mutant protein was developed. In the event that the modified protein is expressed and stable, it is predicted that the acidic interface of frataxin, known to be involved in iron binding and interactions with the iron-sulphur cluster assembly factor IscU, would be impaired.

The Fitts task reveals impairments in planning and online control of movement in Friedreich ataxia: reduced cerebellar-cortico connectivity?

Friedreich ataxia (FRDA) is the most common of the inherited ataxias. We have suggested that people with FRDA may have impairment in cognitive and/or psychomotor capacity either due to disturbance of projections of the cerebellum to the cortex, direct cortical pathology or perhaps both. To further explore this possibility, we used a movement task incorporating Fitts' Law, a robust description of the relationship between movement time and accuracy in goal-directed aiming movements. By manipulating task difficulty, according to target size and distance, we were able to quantify processes related to motor planning in 10 individuals with FRDA and 10 matched control participants. Compared to control participants, people with FRDA were significantly disadvantaged in terms of movement time to targets with an increasing index of difficulty. Successful completion of this task requires both preplanning of movement and online error detection and correction. The cerebellum and its connections to the frontal cortex via cerebro-ponto-cerebello-thalamo-cerebral loops are fundamental to both processes. These results lend further support to our contention that in FRDA these loops are impaired, reflecting a failure to access prefrontal/anterior regions necessary for effective management of preplanning of movement and online error correction.

Neurodegeneration in friedreich's ataxia is associated with a mixed activation pattern of the brain. A fMRI study

Friedreich's ataxia (FRDA) is associated with a distributed pattern of neurodegeneration in the spinal cord and the brain secondary to selective neuronal loss. We used functional MR Imaging (fMRI) to explore brain activation in FRDA patients during two motor-sensory tasks of different complexity, i.e. continuous hand tapping and writing of "8" figure, with the right dominant hand and without visual feedback. Seventeen FRDA patients and two groups of age-matched healthy controls were recruited. Task execution was monitored and recorded using MR-compatible devices. Hand tapping was correctly performed by 11 (65%) patients and writing of the "8" by 7 (41%) patients. After correction for behavioral variables, FRDA patients showed in both tasks areas of significantly lower activation in the left primary sensory-motor cortex and right cerebellum. Also left thalamus and right dorsolateral prefrontal cortex showed hypo-activation during hand tapping. During writing of the "8" task FRDA patients showed areas of higher activation in the right parietal and precentral cortex, globus pallidus, and putamen. Activation of right parietal cortex, anterior cingulum, globus pallidus, and putamen during writing of the "8" increased with severity of the neurological deficit. In conclusion fMRI demonstrates in FRDA a mixed pattern constituted by areas of decreased activation and areas of increased activation. The decreased activation in the primary motor cortex and cerebellum presumably reflects a regional neuronal damage, the decreased activation of the left thalamus and primary sensory cortex could be secondary to deafferentation phenomena, and the increased activation of right parietal cortex and striatum might have a possible compensatory significance.

Superior cerebellar peduncle atrophy in Friedreich's ataxia correlates with disease symptoms

Friedreich's ataxia (FRDA) is the most common early onset inherited ataxia with clinical manifestations, including gradual progression of unremitting cerebellar-sensory ataxia, peripheral sensory loss, loss of lower limb tendon reflexes and hypertrophic cardiomyopathy. Although atrophy of the superior cerebellar peduncle (SCP) has been reported in several magnetic resonance imaging (MRI) studies of FRDA, the relationship of SCP changes to genetic and clinical features of FRDA has not been investigated. We acquired T1-weighted MRI scans in 12 right-handed individuals with FRDA, homozygous for a GAA expansion in intron 1 of FXN, as well as 13 healthy age-matched controls. The corrected cross-sectional areas of the right (left) SCP in the individuals with FRDA (R, 20 ± 7.9 mm(2); L, 25 ± 5.6 mm(2)) were significantly smaller than for controls (R, 68 ± 16 mm(2); L, 78 ± 17 mm(2)) (p < 0.001). The SCP volumes of individuals with FRDA were negatively correlated with Friedreich's ataxia rating scale score (r = -0.553) and disease duration (r = -0.541), and positively correlated with the age of onset (r = 0.548) (p < 0.05). These findings suggest that structural MR imaging of the SCP can provide a surrogate marker of disease severity in FRDA and support the potential role of structural MRI as a biomarker in the evaluation of neurodegenerative diseases and therapies.

Impaired inhibition of prepotent motor tendencies in Friedreich ataxia demonstrated by the Simon interference task

Friedreich ataxia (FRDA) is the most common of the genetically inherited ataxias. We recently demonstrated that people with FRDA have impairment in motor planning - most likely because of pathology affecting the cerebral cortex and/or cerebello-cortical projections. We used the Simon interference task to examine how effective 13 individuals with FRDA were at inhibiting inappropriate automatic responses associated with stimulus-response incompatibility in comparison with control participants. Participants had to respond to arrow targets according to two features which were either congruent or incongruent. We found that individuals with FRDA were differentially affected in reaction time to incongruent, compared with congruent stimuli, when compared with control participants. There was a significant negative correlation between age of onset and the incongruency effect, suggesting an impact of FRDA on the developmental unfolding of motor cognition, independent of the effect of disease duration. Future neuroimaging studies will be required to establish whether this dysfunction is due to cerebellar impairment disrupting cerebro-ponto-cerebello-thalamo-cerebral loops (and thus cortical function), direct primary cortical pathology, or a possible combination of the two.

Ocular motor fixation deficits in Friedreich ataxia

Friedreich ataxia (FRDA) is the most common genetic cause of ataxia with a prevalence of approximately 1 in 29,000. Ocular motor abnormalities are common in FRDA and include fixation instability, saccadic dysmetria, and vestibular dysfunction. It has not yet been determined whether aspects of spatial attention, which are closely coupled to eye movements, are similarly compromised in FRDA. This study examined attentional engagement and disengagement of eye movements in FRDA using a gap overlap task. Thirteen individuals with genetically confirmed FRDA and 12 age-matched unaffected controls participated in the experiment. The gap overlap paradigm was used to examine the effect of early (gap condition), simultaneous (null condition), or late (overlap condition) removal of a central fixation on saccadic latency to a peripheral target stimulus. Although the FRDA group showed a larger gap effect (i.e., difference in saccadic latencies between the overlap and gap condition), these participants demonstrated a greater difference in latencies in the overlap relative to the null condition, suggestive of deficits within the disengagement process of attentional orienting. We propose a role for the cerebellum in these deficits in the disengagement of spatial attention based on evidence of cerebellar connectivity with regions involved in exogenous shifts of attention. The significant correlations between saccadic latency and disease severity as measured by the Friedreich Ataxia Rating Scale further support the proposal that saccadic latency might be useful as a surrogate marker of disease severity and progression in future clinical trials in FRDA.