A combined voxel-based morphometry and 1H-MRS study in patients with Friedreich's ataxia

Retinal hypoplasia and degeneration result in vision loss in Friedreich ataxia

OBJECTIVE

Friedreich ataxia (FRDA) is an inherited condition caused by a GAA triplet repeat (GAA-TR) expansion in the FXN gene. Clinical features of FRDA include ataxia, cardiomyopathy, and in some, vision loss. In this study, we characterize features of vision loss in a large cohort of adults and children with FRDA.

METHODS

Using optical coherence tomography (OCT), we measured peripapillary retinal nerve fiber layer (RNFL) thickness in 198 people with FRDA, and 77 controls. Sloan letter charts were used to determine visual acuity. RNFL thickness and visual acuity were compared to measures of disease severity obtained from the Friedreich Ataxia Clinical Outcomes Measures Study (FACOMS).

RESULTS

The majority of patients, including children, had pathologically thin RNFLs (mean = 73 ± 13 μm in FRDA; 98 ± 9 μm in controls) and low-contrast vision deficits early in the disease course. Variability in RNFL thickness in FRDA (range: 36 to 107 μm) was best predicted by disease burden (GAA-TR length X disease duration). Significant deficits in high-contrast visual acuity were apparent in patients with an RNFL thickness of ≤68 μm. RNFL thickness decreased at a rate of -1.2 ± 1.4 μm/year and reached 68 μm at a disease burden of approximately 12,000 GAA years, equivalent to disease duration of 17 years for participants with 700 GAAs.

INTERPRETATION

These data suggest that both hypoplasia and subsequent degeneration of the RNFL may be responsible for the optic nerve dysfunction in FRDA and support the development of a vision-directed treatment for selected patients early in the disease to prevent RNFL loss from reaching the critical threshold.

Brain MRI detects early-stage alterations and disease progression in Friedreich ataxia

Friedreich ataxia is a progressive neurodegenerative disorder characterized by cerebellar and spinal atrophy. However, studies to elucidate the longitudinal progression of the pathology in the brain are somewhat inconsistent and limited, especially for early-stage Friedreich ataxia. Using a multimodal neuroimaging protocol, combined with advanced analysis methods, we sought to identify macrostructural and microstructural alterations in the brain of patients with early-stage Friedreich ataxia to better understand its distribution patterns and progression. We enrolled 28 patients with Friedreich ataxia and 20 age- and gender-matched controls. Longitudinal clinical and imaging data were collected in the patients at baseline, 12, 24 and 36 months. Macrostructural differences were observed in patients with Friedreich ataxia, compared to controls, including lower volume of the cerebellar white matter (but not cerebellar grey matter), superior cerebellar peduncle, thalamus and brainstem structures, and higher volume of the fourth ventricle. Diffusion tensor imaging and fixel-based analysis metrics also showed microstructural differences in several brain regions, especially in the cerebellum and corticospinal tract. Over time, many of these macrostructural and microstructural alterations progressed, especially cerebellar grey and white matter volumes, and microstructure of the superior cerebellar peduncle, posterior limb of the internal capsule and superior corona radiata. In addition, linear regressions showed significant associations between many of those imaging metrics and clinical scales. This study provides evidence of early-stage macrostructural and microstructural alterations and of progression over time in the brain in Friedreich ataxia. Moreover, it allows to non-invasively map such brain alterations over a longer period (3 years) than any previous study, and identifies several brain regions with significant involvement in the disease progression besides the cerebellum. We show that fixel-based analysis of diffusion MRI data is particularly sensitive to longitudinal change in the cerebellar peduncles, as well as motor and sensory white matter tracts. In combination with other morphometric measures, they may therefore provide sensitive imaging biomarkers of disease progression for clinical trials.

Multiway sparse distance weighted discrimination

Modern data often take the form of a multiway array. However, most classification methods are designed for vectors, i.e., 1-way arrays. Distance weighted discrimination (DWD) is a popular high-dimensional classification method that has been extended to the multiway context, with dramatic improvements in performance when data have multiway structure. However, the previous implementation of multiway DWD was restricted to classification of matrices, and did not account for sparsity. In this paper, we develop a general framework for multiway classification which is applicable to any number of dimensions and any degree of sparsity. We conducted extensive simulation studies, showing that our model is robust to the degree of sparsity and improves classification accuracy when the data have multiway structure. For our motivating application, magnetic resonance spectroscopy (MRS) was used to measure the abundance of several metabolites across multiple neurological regions and across multiple time points in a mouse model of Friedreich's ataxia, yielding a four-way data array. Our method reveals a robust and interpretable multi-region metabolomic signal that discriminates the groups of interest. We also successfully apply our method to gene expression time course data for multiple sclerosis treatment. An R implementation is available in the package MultiwayClassification at http://github.com/lockEF/MultiwayClassification.

Increased brain tissue sodium concentration in Friedreich ataxia: A multimodal MR imaging study

In patients with Friedreich ataxia, structural MRI is typically used to detect abnormalities primarily in the brainstem, cerebellum, and spinal cord. The aim of the present study was to additionally investigate possible metabolic changes in Friedreich ataxia using in vivo sodium MRI that may precede macroanatomical alterations, and to explore potential associations with clinical parameters of disease progression. Tissue sodium concentration across the whole brain was estimated from sodium MRI maps acquired at 3 T and compared between 24 patients with Friedreich ataxia (21-57 years old, 13 females) and 23 controls (21-60 years old, 12 females). Tensor-based morphometry was used to assess volumetric changes. Total sodium concentrations and volumetric data in brainstem and cerebellum were correlated with clinical parameters, such as severity of ataxia, activity of daily living and disability stage, age, age at onset, and disease duration. Compared to controls, patients showed reduced brain volume in the right cerebellar lobules I-V (difference in means: -0.039% of total intracranial volume [TICV]; Cohen's d = 0.83), cerebellar white matter (WM) (-0.105%TICV; d = 1.16), and brainstem (-0.167%TICV; d = 1.22), including pons (-0.102%TICV; d = 1.00), medulla (-0.036%TICV; d = 1.72), and midbrain (-0.028%TICV; d = 1.05). Increased sodium concentration was additionally detected in the total cerebellum (difference in means: 2.865 mmol; d = 0.68), and in several subregions with highest effect sizes in left (5.284 mmol; d = 1.01) and right cerebellar lobules I-V (5.456 mmol; d = 1.00), followed by increases in the vermis (4.261 mmol; d = 0.72), and in left (2.988 mmol; d = 0.67) and right lobules VI-VII (2.816 mmol; d = 0.68). In addition, sodium increases were also detected in all brainstem areas (3.807 mmol; d = 0.71 to 5.42 mmol; d = 1.19). After controlling for age, elevated total sodium concentrations in right cerebellar lobules IV were associated with younger age at onset (r = -0.43) and accordingly with longer disease duration in patients (r = 0.43). Our findings support the potential of in vivo sodium MRI to detect metabolic changes of increased total sodium concentration in the cerebellum and brainstem, the key regions in Friedreich ataxia. In addition to structural changes, sodium changes were present in cerebellar hemispheres and vermis without concomitant significant atrophy. Given the association with age at disease onset or disease duration, metabolic changes should be further investigated longitudinally and in larger cohorts of early disease stages to determine the usefulness of sodium MRI as a biomarker for early neuropathological changes in Friedreich ataxia and efficacy measure for future clinical trials.

Functional MRI Studies in Friedreich's Ataxia: A Systematic Review

Friedreich's ataxia (FRDA) is an inherited neurodegenerative movement disorder with early onset, widespread cerebral and cerebellar pathology, and no cure still available. Functional MRI (fMRI) studies, although currently limited in number, have provided a better understanding of brain changes in people with FRDA. This systematic review aimed to provide a critical overview of the findings and methodologies of all fMRI studies conducted in genetically confirmed FRDA so far, and to offer recommendations for future study designs. About 12 cross-sectional and longitudinal fMRI studies, included 198 FRDA children and young adult patients and, 205 healthy controls (HCs), according to the inclusion criteria. Details regarding GAA triplet expansion and demographic and clinical severity measures were widely reported. fMRI designs included motor and cognitive task paradigms, and resting-state studies, with widespread changes in functionally activated areas and extensive variability in study methodologies. These studies highlight a mixed picture of both hypoactivation and hyperactivation in different cerebral and cerebellar brain regions depending on fMRI design and cohort characteristics. Functional changes often correlate with clinical variables. In aggregate, the findings provide support for cerebro-cerebellar loop damage and the compensatory mechanism hypothesis. Current literature indicates that fMRI is a valuable tool for gaining in vivo insights into FRDA pathology, but addressing that its limitations would be a key to improving the design, interpretation, and generalizability of studies in the future.

Longitudinal structural brain changes in Friedreich ataxia depend on disease severity: the IMAGE-FRDA study

BACKGROUND

Friedreich ataxia is an inherited neurodegenerative disease, with cerebral and cerebellar pathology evident. Despite an increased understanding of its neuropathology, disease progression in this disease remains poorly understood. This study aimed to characterise longitudinal change in brain structure using a multi-modal approach across cerebral and cerebellar grey and white matter.

METHODS

T1-weighted, diffusion-tensor, and magnetisation transfer magnetic resonance images were obtained from 28 individuals with Friedreich ataxia and 29 age- and gender-matched controls at two time-points, 2 years apart. Region-of-interest and exploratory between-group comparisons assessed changes in brain macrostructure (cerebellar lobule volume, cerebral cortical thickness/gyrification, brain white matter volume) and microstructure (white matter fractional anisotropy, mean/axial/radial diffusivity, magnetisation transfer ratio). Rates of change were correlated against change in neurological severity, Time 1 severity, and onset age.

RESULTS

Individuals with Friedreich ataxia had a greater rate of white matter volume loss than controls in the superior cerebellar peduncles and right peri-thalamic/posterior cerebral regions, and greater reduction in left primary motor cortex gyrification. Greater cerebellar/brainstem white matter volume loss and right dorsal premotor gyrification loss was observed amongst individuals with less severe neurological symptoms at Time 1. Conversely, cerebral atrophy and changes in axial diffusivity were observed in individuals with more severe Time 1 symptoms. Progression in radial diffusivity was more pronounced amongst individuals with earlier disease onset. Greater right ventral premotor gyrification loss correlated with greater neurological progression.

CONCLUSION

Heterogeneity in Friedreich ataxia progression is observed at the neurobiological level, with evidence of earlier cerebellar and later cerebral degeneration.

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.

Antioxidant Therapies and Oxidative Stress in Friedreich´s Ataxia: The Right Path or Just a Diversion?

Friedreich´s ataxia is the commonest autosomal recessive ataxia among population of European descent. Despite the huge advances performed in the last decades, a cure still remains elusive. One of the most studied hallmarks of the disease is the increased production of oxidative stress markers in patients and models. This feature has been the motivation to develop treatments that aim to counteract such boost of free radicals and to enhance the production of antioxidant defenses. In this work, we present and critically review those "antioxidant" drugs that went beyond the disease´s models and were approved for its application in clinical trials. The evaluation of these trials highlights some crucial aspects of the FRDA research. On the one hand, the analysis contributes to elucidate whether oxidative stress plays a central role or whether it is only an epiphenomenon. On the other hand, it comments on some limitations in the current trials that complicate the analysis and interpretation of their outcome. We also include some suggestions that will be interesting to implement in future studies and clinical trials.

Multiple mechanisms underpin cerebral and cerebellar white matter deficits in Friedreich ataxia: The IMAGE-FRDA study

Friedreich ataxia is a progressive neurodegenerative disorder with reported abnormalities in cerebellar, brainstem, and cerebral white matter. White matter structure can be measured using in vivo neuroimaging indices sensitive to different white matter features. For the first time, we examined the relative sensitivity and relationship between multiple white matter indices in Friedreich ataxia to more richly characterize disease expression and infer possible mechanisms underlying the observed white matter abnormalities. Diffusion-tensor, magnetization transfer, and T1-weighted structural images were acquired from 31 individuals with Friedreich ataxia and 36 controls. Six white matter indices were extracted: fractional anisotropy, diffusivity (mean, axial, radial), magnetization transfer ratio (microstructure), and volume (macrostructure). For each index, whole-brain voxel-wise between-group comparisons and correlations with disease severity, onset age, and gene triplet-repeat length were undertaken. Correlations between pairs of indices were assessed in the Friedreich ataxia cohort. Spatial similarities in the voxel-level pattern of between-group differences across the indices were also assessed. Microstructural abnormalities were maximal in cerebellar and brainstem regions, but evident throughout the brain, while macroscopic abnormalities were restricted to the brainstem. Poorer microstructure and reduced macrostructural volume correlated with greater disease severity and earlier onset, particularly in peri-dentate nuclei and brainstem regions. Microstructural and macrostructural abnormalities were largely independent. Reduced fractional anisotropy was most strongly associated with axial diffusivity in cerebral tracts, and magnetization transfer in cerebellar tracts. Multiple mechanisms likely underpin white matter abnormalities in Friedreich ataxia, with differential impacts in cerebellar and cerebral pathways.

Neurochemical profiles in hereditary ataxias: A meta-analysis of Magnetic Resonance Spectroscopy studies

Magnetic resonance spectroscopy (MRS) is applied to investigate the neurochemical profiles of degenerative hereditary ataxias. This meta-analysis provides a quantitative review and reappraisal of MRS findings in spinocerebellar ataxias (SCA) and Friedreich ataxia (FA) available to date. From each study, changes in N-acetyl aspartate (NAA), choline-containing compounds (Cho) and myo-Inositol (mI) ratios to total creatine (Cr) were calculated for groups of patients (1499 patients in total: SCA1 = 223, SCA2 = 298, SCA3 = 711, SCA6 = 165, and FA = 102) relative to their own control group, mostly in cerebellum and pons. SCA1, 2, 3, 6, and FA patients showed overall decreased NAA/Cr compared to controls. Decreased Cho/Cr was visible in SCA1, 2, and 3 and elevated mI/Cr in SCA2 patients in cerebellum. In SCA6 and FA Cho/Cr and mI/Cr did not differ with respect to controls but SCA6 patients indicated higher Cho/Cr compared to SCA1 patients in cerebellum. SCA2 subjects showed the lowest NAA/Cr and Cho/Cr in cerebellum and the highest mI/Cr compared to controls and other genotypes, and therefore the most promising results for a potential biomarker.

Developmental and neurodegenerative damage in Friedreich's ataxia

BACKGROUND AND PURPOSE

Friedreich's ataxia (FRDA) is the most common autosomal-recessive ataxia worldwide. It is characterized by early onset, sensory abnormalities and slowly progressive ataxia. All magnetic resonance imaging (MRI)-based studies have focused on the evaluation of adult patients. Therefore, we designed a cross-sectional multimodal MRI-based study to investigate the anatomical substrates involved in the early stages of FRDA.

METHODS

We enrolled 37 patients (12 children) and 38 controls. All subjects underwent MRI in a 3T device to assess gray and white matter. We used measures from FreeSurfer and CERES to evaluate the cerebral and cerebellar cortices. The T1 multiatlas assessed deep gray matter. The diffusion tensor imaging multiatlas was used to investigate microstructural abnormalities in brain white matter and SpineSeg was used to assess the cervical spinal cord. All analyses were corrected for multiple comparisons.

RESULTS

Comparison with age-matched controls showed that pediatric patients have spinal cord, inferior cerebellar peduncle and red nucleus damage. In contrast, adult patients showed more widespread white matter damage than pediatric patients. With regard to gray matter, we found cortical thinning at the left central sulcus and volumetric reduction in the thalami and hippocampi only in adult patients. Finally, values of fractional anisotropy in adult patients and radial diffusivity in pediatric patients from the inferior cerebellar peduncle correlated with disease duration and ataxia severity, respectively.

CONCLUSIONS

Structural damage in FRDA begins in the spinal cord and inferior cerebellar peduncle as well as the red nucleus, and progresses to cerebral areas in adulthood. These results shed some light on the early stages of FRDA and highlight potential neuroimaging markers for therapeutic trials.

Neuroimaging Applications in Chronic Ataxias

Magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT) and positron emission tomography (PET) are the main instruments for neuroimaging investigation of patients with chronic ataxia. MRI has a predominant diagnostic role in the single patient, based on the visual detection of three patterns of atrophy, namely, spinal atrophy, cortical cerebellar atrophy and olivopontocerebellar atrophy, which correlate with the aetiologies of inherited or sporadic ataxia. In fact spinal atrophy is observed in Friedreich ataxia, cortical cerebellar atrophy in Ataxia Telangectasia, gluten ataxia and Sporadic Adult Onset Ataxia and olivopontocerebellar atrophy in Multiple System Atrophy cerebellar type. The 39 types of dominantly inherited spinocerebellar ataxias show either cortical cerebellar atrophy or olivopontocerebellar atrophy. T2 or T2* weighted MR images can contribute to the diagnosis by revealing abnormally increased or decreased signal with a characteristic distribution. These include symmetric T2 hyperintensity of the posterior and lateral columns of the cervical spinal cord in Friedreich ataxia, diffuse and symmetric hyperintensity of the cerebellar cortex in Infantile Neuro-Axonal Dystrophy, symmetric hyperintensity of the peridentate white matter in Cerebrotendineous Xanthomatosis, and symmetric hyperintensity of the middle cerebellar peduncles and peridentate white matter, cerebral white matter and corpus callosum in Fragile X Tremor Ataxia Syndrome. Abnormally decreased T2 or T2* signal can be observed with a multifocal distribution in Ataxia Telangectasia and with a symmetric distribution in the basal ganglia in Multiple System Atrophy. T2 signal hypointensity lining diffusely the outer surfaces of the brainstem, cerebellum and cerebrum enables diagnosis of superficial siderosis of the central nervous system. The diagnostic role of nuclear medicine techniques is smaller. SPECT and PET show decreased uptake of radiotracers investigating the nigrostriatal system in Multiple System Atrophy and in patients with Fragile X Tremor Ataxia Syndrome. Semiquantitative or quantitative MRI, SPECT and PET data describing structural, microstructural and functional changes of the cerebellum, brainstem, and spinal cord have been widely applied to investigate physiopathological changes in patients with chronic ataxias. Moreover they can track diseases progression with a greater sensitivity than clinical scales. So far, a few small-size and single center studies employed neuroimaging techniques as surrogate markers of treatment effects in chronic ataxias.

Structural signature in SCA1: clinical correlates, determinants and natural history

Spinocerebellar ataxia type 1 is an autosomal dominant disorder caused by a CAG repeat expansion in ATXN1, characterized by progressive cerebellar and extracerebellar symptoms. MRI-based studies in SCA1 focused in the cerebellum and connections, but there are few data about supratentorial/spinal damage and its clinical relevance. We have thus designed this multimodal MRI study to uncover the structural signature of SCA1. To accomplish that, a group of 33 patients and 33 age-and gender-matched healthy controls underwent MRI on a 3T scanner. All patients underwent a comprehensive neurological and neuropsychological evaluation. We correlated the structural findings with the clinical features of the disease. In addition, we evaluated the disease progression looking at differences in SCA1 subgroups defined by disease duration. Ataxia and pyramidal signs were the main symptoms. Neuropsychological evaluation disclosed cognitive impairment in 53% with predominant frontotemporal dysfunction. Gray matter analysis unfolded cortical thinning of primary and associative motor areas with more restricted impairment of deep structures. Deep gray matter atrophy was associated with motor handicap and poor cognition skills. White matter integrity loss was diffuse in the brainstem but restricted in supratentorial structures. Cerebellar cortical thinning was found in multiple areas and correlated not only with motor disability but also with verbal fluency. Spinal cord atrophy correlated with motor handicap. Comparison of MRI findings in disease duration-defined subgroups identified a peculiar pattern of progressive degeneration.

Functional and Structural Brain Damage in Friedreich's Ataxia

Friedreich's ataxia (FRDA) is a rare hereditary neurodegenerative disorder caused by a GAA repeat expansion in the FXN gene. There is still no cure or quantitative biomarkers reliaby correlating with the progression rate and disease severity. Investigation of functional and structural alterations characterizing white (WM) and gray matter (GM) in FRDA are needed prerequisite to monitor progression and response to treatment. Here we report the results of a multimodal cross-sectional MRI study of FRDA including Voxel-Based Morphometry (VBM), diffusion-tensor imaging (DTI), functional MRI (fMRI), and a correlation analysis with clinical severity scores. Twenty-one early-onset FRDA patients and 18 age-matched healthy controls (HCs) were imaged at 3T. All patients underwent a complete cognitive and clinical assessment with ataxia scales. VBM analysis showed GM volume reduction in FRDA compared to HCs bilaterally in lobules V, VI, VIII (L>R), as well as in the crus of cerebellum, posterior lobe of the vermis, in the flocculi and in the left tonsil. Voxel-wise DTI analysis showed a diffuse fractional anisotropy reduction and mean, radial, axial (AD) diffusivity increase in both infratentorial and supratentorial WM. ROI-based analysis confirmed the results showing differences of the same DTI metrics in cortico-spinal-tracts, forceps major, corpus callosum, posterior thalamic radiations, cerebellar penduncles. Additionally, we observed increased AD in superior (SCP) and middle cerebellar peduncles. The WM findings correlated with age at onset (AAO), short-allelle GAA, and disease severity. The intragroup analysis of fMRI data from right-handed 14 FRDA and 15 HCs showed similar findings in both groups, including activation in M1, insula and superior cerebellar hemisphere (lobules V-VIII). Significant differences emerged only during the non-dominant hand movement, with HCs showing a stronger activation in the left superior cerebellar hemisphere compared to FRDA. Significant correlations were found between AAO and the fMRI activation in cerebellar anterior and posterior lobes, insula and temporal lobe. Our multimodal neuroimaging protocol suggests that MRI is a useful tool to document the extension of the neurological impairment in FRDA.

Cognitive and functional connectivity alterations in Friedreich's ataxia

Objective

The aim of this study was to perform the first resting-state functional MRI (RS-fMRI) analysis in Friedreich's ataxia (FRDA) patients to assess possible brain functional connectivity (FC) differences in these patients, and test their correlations with neuropsychological performances.

Methods

In total, 24 FRDA patients (M/F: 15/9, mean age 31.3 ± 15.0) and 24 healthy controls (HC; M/F: 15/9, mean age 30.7 ± 15.5) were enrolled in this cross-sectional study. All patients underwent a thorough neuropsychological battery, investigating different cognitive domains. RS-fMRI data were analyzed using a seed-based approach, probing the FC of cortical areas potentially referable to specific executive and cognitive functions compromised in FRDA.

Results

Compared to HC, FRDA patients showed overall worse neuropsychological scores in several domains, including global cognitive assessment, spatial memory, visuoperception and visuospatial functions, and executive functions. Analysis of RS-fMRI data showed a higher FC in FRDA patients compared to HC between paracingulate gyri and the medial frontal gryrus, between the superior frontal gyrus and bilateral angular gyri, and between the middle temporal gyrus and the cingulate gyrus, with a reduced FC between the medial frontal gryrus and the cerebellum.

Interpretation

We found a reduction in FC between frontal areas and the contralateral cerebellar cortex in FRDA, in line with the known alteration in cerebello-cortical pathway in this condition. On the other hand, a higher FC between different cortical areas was shown, possibly reflecting a compensatory phenomenon. These results, in conjunction with clinical findings, may shed new light on the pattern of supratentorial and infratentorial involvement, and on dynamics of brain plasticity in this 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.

Cerebellar degeneration affects cortico-cortical connectivity in motor learning networks

The cerebellum plays an important role in motor learning as part of a cortico-striato-cerebellar network. Patients with cerebellar degeneration typically show impairments in different aspects of motor learning, including implicit motor sequence learning. How cerebellar dysfunction affects interactions in this cortico-striato-cerebellar network is poorly understood. The present study investigated the effect of cerebellar degeneration on activity in causal interactions between cortical and subcortical regions involved in motor learning. We found that cerebellar patients showed learning-related increase in activity in two regions known to be involved in learning and memory, namely parahippocampal cortex and cerebellar Crus I. The cerebellar activity increase was observed in non-learners of the patient group whereas learners showed an activity decrease. Dynamic causal modeling analysis revealed that modulation of M1 to cerebellum and putamen to cerebellum connections were significantly more negative for sequence compared to random blocks in controls, replicating our previous results, and did not differ in patients. In addition, a separate analysis revealed a similar effect in connections from SMA and PMC to M1 bilaterally. Again, neural network changes were associated with learning performance in patients. Specifically, learners showed a negative modulation from right SMA to right M1 that was similar to controls, whereas this effect was close to zero in non-learners. These results highlight the role of cerebellum in motor learning and demonstrate the functional role cerebellum plays as part of the cortico-striato-cerebellar network.

Structural signature of classical versus late-onset friedreich's ataxia by Multimodality brain MRI

INTRODUCTION

Friedreich's ataxia (FRDA) is the most common autosomal-recessive ataxia worldwide. It is characterized by early onset, sensory abnormalities, and slowly progressive ataxia. However, some individuals manifest the disease after the age of 25 years and are classified as late-onset FRDA (LOFA). Therefore, we propose a transversal multimodal MRI-based study to investigate which anatomical substrates are involved in classical (cFRDA) and LOFA.

METHODS

We enrolled 36 patients (13 with LOFA) and 29 healthy controls. All subjects underwent magnetic resonance imaging in a 3 T device; three-dimensional high-resolution T1-weighted images and diffusion tensor images were used to assess gray and white matter, respectively. We used T1 multiatlas approach to assess deep gray matter and cortical thickness measures to evaluate cerebral cortex and DTI multiatlas approach to assess white matter. All analyses were corrected for multiple comparisons.

RESULTS

Group comparison showed that both groups presented gray matter atrophy mostly in the motor cortex. Regarding white matter, we found abnormalities in the cerebellar peduncles, pyramidal tracts, midbrain, pons, and medulla oblongata for both groups, but the microstructural abnormalities in the cFRDA group were more widespread. In addition, we found that the corticospinal tract presented more severe microstructural damage in the LOFA group. Finally, the midbrain volume of the cFRDA, but not of the LOFA group, correlated with disease duration (R = -0.552, P = 0.012) and severity (R = -0.783, P < 0.001).

CONCLUSION

The cFRDA and LOFA groups have similar, but not identical neuroimaging damage pattern. These structural differences might help to explain the phenotypic variability observed in FRDA. Hum Brain Mapp 38:4157-4168, 2017. © 2017 Wiley Periodicals, Inc.

Cerebral and cerebellar grey matter atrophy in Friedreich ataxia: the IMAGE-FRDA study

Friedreich ataxia (FRDA) is traditionally associated with neuropathology in the cerebellar dentate nucleus and spinal cord. Growing evidence also suggests involvement of the cerebral and cerebellar cortices, although reports of structural abnormalities remain mixed. This study assessed the structural integrity of cortical grey matter in FRDA, focussing on regions in which pathology may underlie the motor deficits characteristic of this disorder. T1-weighted anatomical magnetic resonance imaging scans were acquired from 31 individuals with FRDA and 37 healthy controls. Cortical thickness (FreeSurfer) and cortical volume (SPM-VBM) were measured in cerebral motor regions-of-interest (primary motor, dorsal and ventral premotor, and supplementary motor areas) alongside unconstrained exploratory analyses of the cerebral and cerebellar cortices. Correlations were assessed between cortical thickness/volume measures and each of disease severity, length of the causative genetic triplet-repeat expansion, and finger-tapping behavioural measures. Individuals with FRDA had significantly reduced cortical thickness, relative to controls, in the premotor and supplementary motor areas. Reduced cortical thickness and/or volume were also observed in the cuneus and precuneus, posterior aspects of the medial and lateral prefrontal cortices, insula, temporal poles, and cerebellar lobules V, VI, and VII. Measures of clinical severity, genetic abnormality, and motor dysfunction correlated with volume loss in the lateral cerebellar hemispheres. These results suggest that atrophy preferentially affects premotor relative to primary areas of the cortical motor system, and also extends to a range of non-motor brain regions. Furthermore, cortical thickness and cortical volume findings were largely divergent, suggesting that each is sensitive to different aspects of neuropathology in FRDA. Overall, this study supports a disease model involving neural aberrations within the cerebral and cerebellar cortices, beyond those traditionally associated with this disorder.

Cognition in Friedreich's ataxia: a behavioral and multimodal imaging study

Objective

Friedreich's ataxia (FRDA) is a spinocerebellar degenerative disorder, in which cognitive deficits are sparsely explored. In this behavioral and multimodal magnetic resonance imaging (MRI) study, we investigated the neurocognitive profile and cortico‐cerebellar dysfunctions underlying executive functioning in individuals with FRDA.

Methods

22 FRDA patients and 22 controls were clinically and neuropsychologically examined. Fifteen of each underwent structural and functional MRI using a verbal‐fluency task with phonemic and semantic conditions. Gray (GM) and white matter (WM) alterations were assessed by means of voxel‐based morphometry and diffusion‐tensor imaging.

Results

The neuropsychological profile demonstrated deficits in verbal fluency, working memory and social cognition. Functional MRI data showed most pronounced group‐differences in phonemic fluency with patients exhibiting enhanced activity in the cerebellum (VI, Crus I), fronto‐insular, premotor and temporo‐occipital regions. The semantic condition only revealed reduced activity in the anterior cerebellum; for overt speech, we found increased activity in the motor cortex. Functional connectivity‐analysis showed higher co‐activation within cerebellar and cortical regions, respectively, and impaired interregional coupling between the cerebellum and fronto‐insular cortex for phonemic processing, which was also related to poorer task performance. GM reduction in FRDA was mainly found in lobule VI, whereas WM degeneration was more pronounced including brainstem, cerebellum, and cortex. Decreased cerebellar GM was associated with enhanced activity in the fronto‐insular cortex, while loss of WM integrity may translate cortico‐cerebellar pathway disruptions.

Interpretation

The pattern of increased neural response with both cerebellar and cortical involvement underlying executive functioning indicates functional reorganization driven by disease‐related structural damage in FRDA.

Longitudinal magnetic resonance imaging study shows progressive pyramidal and callosal damage in Friedreich's ataxia

INTRODUCTION

Spinal cord and peripheral nerves are classically known to be damaged in Friedreich's ataxia, but the extent of cerebral involvement in the disease and its progression over time are not yet characterized. The aim of this study was to evaluate longitudinally cerebral damage in Friedreich's ataxia.

METHODS

We enrolled 31 patients and 40 controls, which were evaluated at baseline and after 1 and 2 years. To assess gray matter, we employed voxel-based morphometry and cortical thickness measurements. White matter was evaluated using diffusion tensor imaging. Statistical analyses were both cross-sectional and longitudinal (corrected for multiple comparisons).

RESULTS

Group comparison between patients and controls revealed widespread macrostructural differences at baseline: gray matter atrophy in the dentate nuclei, brainstem, and precentral gyri; and white matter atrophy in the cerebellum and superior cerebellar peduncles, brainstem, and periventricular areas. We did not identify any longitudinal volumetric change over time. There were extensive microstructural alterations, including superior cerebellar peduncles, corpus callosum, and pyramidal tracts. Longitudinal analyses identified progressive microstructural abnormalities at the corpus callosum, pyramidal tracts, and superior cerebellar peduncles after 1 year of follow-up.

CONCLUSION

Patients with Friedreich's ataxia present more widespread gray and white matter damage than previously reported, including not only infratentorial areas, but also supratentorial structures. Furthermore, patients with Friedreich's ataxia have progressive microstructural abnormalities amenable to detection in a short-term follow-up.

MRI Texture Analysis Reveals Bulbar Abnormalities in Friedreich Ataxia

BACKGROUND AND PURPOSE

Texture analysis is an image processing technique that can be used to extract parameters able to describe meaningful features of an image or ROI. Texture analysis based on the gray level co-occurrence matrix gives a second-order statistical description of the image or ROI. In this work, the co-occurrence matrix texture approach was used to extract information from brain MR images of patients with Friedreich ataxia and a control group, to see whether texture parameters were different between these groups. A longitudinal analysis was also performed.

MATERIALS AND METHODS

Twenty patients and 21 healthy controls participated in the study. Both groups had 2 sets of T1-weighted MR images obtained 1 year apart for every subject. ROIs chosen for analysis were the medulla oblongata and pons. Texture parameters were obtained for these ROIs for every subject, for the 2 sets of images. These parameters were compared longitudinally within groups and transversally between groups.

RESULTS

The comparison between patients and the control group showed a significant differences for the medulla oblongata (t test, P < .05, Bonferroni-corrected) but did not show a statistically significant difference for the pons. Longitudinal comparison of images obtained 1 year apart did not show differences for either patients or for controls, in any of the analyzed structures.

CONCLUSIONS

Gray level co-occurrence matrix-based texture analysis showed statistically significant differences for the medulla oblongata of patients with Friedreich ataxia compared with controls. These results highlight the medulla as an important site of damage in Friedreich ataxia.

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.

Regional Cerebral Disease Progression in Friedreich's Ataxia: A Longitudinal Diffusion Tensor Imaging Study

BACKGROUND AND PURPOSE

Imaging biomarkers of disease progression are desirable in inherited ataxias. MRI has demonstrated brain damage in Friedreich ataxia (FRDA) in form of regional atrophy of the medulla, peridentate cerebellar white matter (WM) and superior cerebellar peduncles (visible in T1-weighted images) and of change of microstructural characteristics of WM tracts of the brainstem, cerebellar peduncles, cerebellum, and supratentorial structures (visible through diffusion-weighted imaging). We explored the potential of brain MR morphometry and diffusion tensor imaging (DTI) to track the progression of neurodegeneration in FRDA.

METHODS

Eight patients (5F, 3M; age 13.4-41.2 years) and 8 healthy controls (2F, 6M; age 26.2-48.3 years) underwent 2 MRI examinations (mean 3.9 and 4.1 years apart, respectively) on the same 1.5T scanner. The protocol included 3D T1-weighted images and axial diffusion-weighted images (b-value 1,000 s/mm(2)) for calculating maps of fractional anisotropy, mean, axial and radial diffusivity, and mode of anisotropy. Tensor-based morphometry was used to investigate regional volume changes and tract-based spatial statistics was used to investigate microstructural changes in WM tracts.

RESULTS

Longitudinal analyses showed no differences in regional volume changes but a significant difference in axial diffusivity changes in cerebral and corpus callosum WM of patients as compared to controls (mean longitudinal rate of change for axial diffusivity: -.02 × 10(-3) mm(2)/s/year in patients vs. .01 × 10(-3) mm(2)/s/year in controls). No correlation with number of triplets, disease duration, and worsening of the clinical deficit was observed.

CONCLUSION

DTI can track brain microstructural changes in FRDA and can be considered a potential biomarker of disease progression.

Cerebellar pathology in Friedreich's ataxia: atrophied dentate nuclei with normal iron content

BACKGROUND

In Friedreich's ataxia (FA) the genetically decreased expression of the mitochondrial protein frataxin leads to disturbance of the mitochondrial iron metabolism. Within the cerebellum the dentate nuclei (DN) are primarily affected. Histopathological studies show atrophy and accumulation of mitochondrial iron in DN. Dentate iron content has been suggested as a biomarker to measure the effects of siderophores/antioxidant treatment of FA. We assessed the iron content and the volume of DN in FA patients and controls based on ultra-high-field MRI (7 Tesla) images.

METHODS

Fourteen FA patients (mean age 38.1 yrs) and 14 age- and gender-matched controls participated. Multi-echo gradient echo and susceptibility weighted imaging (SWI) sequences were acquired on a 7 T whole-body scanner. For comparison SWI images were acquired on a 1.5 T MR scanner. Volumes of the DN and cerebellum were assessed at 7 and 1.5 T, respectively. Parametric maps of T2 and T2* sequences were created and proton transverse relaxation rates were estimated as a measure of iron content.

RESULTS

In FA, the DN and the cerebellum were significantly smaller compared to controls. However, proton transverse relaxation rates of the DN were not significantly different between both groups.

CONCLUSIONS

Applying in vivo MRI methods we could demonstrate significant atrophy of the DN in the presence of normal iron content. The findings suggest that relaxation rates are not reliable biomarkers in clinical trials evaluating the potential effect of FA therapy.

Myelin paucity of the superior cerebellar peduncle in individuals with Friedreich ataxia: an MRI magnetization transfer imaging study

The dentate nucleus (DN) is the major relay station for neural connection between the cerebellum and cerebrum via the thalamus, and is a significant component of the neuropathological profile of Friedreich ataxia (FRDA). We have previously shown that the size of the superior cerebellar peduncle (SCP), which links the DN to cortical and subcortical structures via the thalamus, is significantly reduced in individuals with FRDA compared to control participants. This study used magnetization transfer imaging (MTI) to examine and contrast the integrity of white matter (WM) in the SCP and the corpus callosum (CC) (control region) in ten individuals with FRDA and ten controls. Individuals with FRDA demonstrated a significant reduction in the magnetization transfer ratio (MTR) in the SCP compared to control participants. However, there was no significant difference between groups in MTR in the CC. When comparing regions within groups, there was a significant reduction in MTR in the SCP compared to CC in participants with FRDA only. We suggest that the reduction in MTR in the SCP may be indicative of lack of myelin secondary to axonal loss and oligodendroglial dysfunction in WM tracts in individuals with FRDA.

Neuroanatomical correlates of depression in Friedreich's ataxia: a voxel-based morphometry study

Affective disorders have been increasingly recognized in neurodegenerative diseases and often result in poor quality of life. However, the frequency, clinical relevance, and anatomical substrate of depression in Friedreich's ataxia were not yet evaluated. We assessed 22 patients with Friedreich's ataxia for major depression using Beck Depression Inventory and cerebral 3 T MRI scans. We then employed whole-brain voxel-based morphometry analyses on volumetric T1 datasets to compare tissue loss between patients with and without major depression. Patients (36.3 %) fulfilled criteria for major depression (8/22). Mean Beck Depression Inventory (BDI) score was 9.63 ± 8.95 and the depressive group had significantly higher score compared to non-depressive group (18.5 ± 8.6 vs 4.4 ± 2.9, p < 0.001). There was no correlation between Beck Depression Inventory score and age of patients, ataxia severity, age at onset, or duration of the disease. The comparison between patient groups found no significant differences of white matter volumes. In contrast, we found reduction of gray matter volumes in the depressive group in medial and orbital region of frontal lobe and anterior cingulate gyri (p < 0.001). Regression analyses have shown that BDI scores were inversely correlated with gray matter volume at right superior frontal gyrus. Major depression is frequent in Friedreich's ataxia and possibly under recognized. Our results strongly suggest that this may not be a simply reactive phenomenon, but rather associated to structural abnormalities.

Magnetic resonance imaging biomarkers in patients with progressive ataxia: current status and future direction

A diagnostic challenge commonly encountered in neurology is that of an adult patient presenting with ataxia. The differential is vast and clinical assessment alone may not be sufficient due to considerable overlap between different causes of ataxia. Magnetic resonance (MR)-based biomarkers such as voxel-based morphometry, MR spectroscopy, diffusion-weighted and diffusion-tensor imaging and functional MR imaging are gaining great attention for their potential as indicators of disease. A number of studies have reported correlation with clinical severity and underlying pathophysiology, and in some cases, MR imaging has been shown to allow differentiation of conditions causing ataxia. However, despite recent advances, their sensitivity and specificity vary. In addition, questions remain over their validity and reproducibility, especially when applied in routine clinical practice. This article extensively reviews the current literature regarding MR-based biomarkers for the patient with predominantly adult-onset ataxia. Imaging features characteristic of a particular ataxia are provided and features differentiating ataxia groups and subgroups are discussed. Finally, discussion will turn to the feasibility of applying these biomarkers in routine clinical practice.

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.

White Matter Atrophy in Patients with Mesial Temporal Lobe Epilepsy: Voxel-Based Morphometry Analysis of T1- and T2-Weighted MR Images

Introduction. Mesial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis is highly refractory to clinical treatment. MRI voxel-based morphometry (VBM) of T1-weighted images has revealed a widespread pattern of gray matter (GM) and white matter (WM) atrophy in MTLE. Few studies have investigated the role of T2-weighted images in revealing WM atrophy using VBM. Objectives. To compare the results of WM atrophy between T1- and T2-weighted images through VBM. Methods. We selected 28 patients with left and 27 with right MTLE and 60 normal controls. We analyzed T1- and T2- weighted images with SPM8, using VBM/DARTEL algorithm to extract maps of GM and WM. The second level of SPM was used to investigate areas of WM atrophy among groups. Results. Both acquisitions showed bilateral widespread WM atrophy. T1-weighted images showed higher sensibility to detect areas of WM atrophy in both groups of MTLE. T2-weighted images also showed areas of WM atrophy in a more restricted pattern, but still bilateral and with a large area of superposition with T1-weighted images. Conclusions. In MTLE, T1-weighted images are more sensitive to detect subtle WM abnormalities using VBM, compared to T2 images, although both present a good superposition of statistical maps.

A review of Friedreich ataxia clinical trial results

There are now 21 agents or classes of therapeutic agents in the Friedreich ataxia research pipeline (http://www.curefa.org/pipeline.html) that have been developed in the 15 years since the discovery of the frataxin gene, with the ongoing characterization of its mutations and the resulting molecular pathology. Twenty-four studies are currently posted on ClinicalTrials.gov. Twenty-seven works discussing the results of clinical trials in Friedreich ataxia have been published. In 2010, 42 public (National Institutes of Health) and private (Friedreich Ataxia Research Alliance, Muscular Dystrophy Association, and National Ataxia Foundation) grants were funded for translational and clinical research in Friedreich ataxia. Millions of dollars from public, private, and industry-based initiatives have been dedicated to research in Friedreich ataxia therapeutics. Despite this vigorous international effort, there is as yet no proven disease-modifying therapy for Friedreich ataxia.

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.

A functional MRI study of motor dysfunction in Friedreich's ataxia

Friedreich's ataxia (FRDA) is the most common form of hereditary ataxia. In addition to proximal spinal cord and brain stem atrophy, mild to moderate atrophy of the cerebellum has been reported in advanced FRDA. The aim of this study was to examine dysfunction in motor-related areas involved in the execution of finger tapping tasks in individuals with FRDA, and to investigate functional re-organization of cortico-cerebellar, cortico-striatal and parieto-frontal loops as a result of the cerebellar pathology. Thirteen right-handed individuals with FRDA and fourteen right-handed controls participated. Functional MRI images were acquired during four different finger tapping tasks consisting of visually cued regular and irregular single finger tapping tasks, a self-paced regular finger tapping task, and a visually cued multi-finger tapping task. Both groups showed significant activation of the motor-related network including the pre-central cortex and supplementary motor area bilaterally; the left primary motor cortex, somatosensory cortex and putamen; and the right cerebellum. During the visually cued regular finger tapping task, the right hemisphere of the cerebellar cortex, bilateral supplementary motor areas and right inferior parietal cortex showed higher activation in the healthy control group, while in individuals with FRDA the left premotor cortex, left somatosensory cortex and left inferior parietal cortex were more active. In addition, during the visually cued irregular finger tapping task, the right middle temporal gyrus in the control group and the right superior parietal lobule and left superior and middle temporal gyri in the individuals with FRDA showed higher activation. During visually cued multi-finger tapping task, the control group showed higher activation in the bilateral middle frontal gyri, bilateral somatosensory cortices, bilateral inferior parietal lobules, left premotor cortex, left supplementary area, right superior frontal gyrus and right cerebellum, while individuals with FRDA showed increased activity in the left inferior parietal lobule, left primary motor cortex, left middle occipital gyrus, right somatosensory cortex and the left cerebellum. Only the right crus I/II of the cerebellum showed higher activation in individuals with FRDA during the self-paced regular finger tapping task, whereas wide-spread regions including the left superior frontal gyrus, left central opercular cortex, left somatosensory cortex, left putamen, right cerebellum, bilateral primary motor cortices, bilateral inferior parietal lobules and the left insula were more active in the control group. Although the pattern of the BOLD signal from the putamen was different during the self-paced regular finger tapping task to the other tasks in controls, in individuals with FRDA there was no distinction of the signal between the tasks suggesting that primary cerebellar pathology may cause secondary basal ganglia dysregulation. While individuals with FRDA tapped at a slightly lower rate (0.59Hz) compared with controls (0.74Hz) they showed significantly decreased activity of the SMA and the inferior parietal lobule, which may suggest disruption to the fronto-parietal connections. These findings suggest that the motor impairments in individuals with FRDA result from dysfunction extending beyond the spinal cord and cerebellum to include sub-cortical and cortical brain regions.

Cerebellar atrophy is infrequently [corrected] associated with non-paraneoplastic sensory neuronopathy

Sensory neuronopathies (SN) are peripheral nervous system disorders associated with degeneration of dorsal root ganglion neurons. Despite the evidence of a defective proprioceptive sensory input in SN,the prominent gait and truncal ataxia raises the question of a concomitant involvement of the cerebellum.

OBJECTIVE

To evaluate cerebellar atrophy in SN.

METHOD

We analyzed MRI-based volumetry of anterior lobe (paleocerebellum) and total cerebellum in patients with non-paraneoplastic chronic SN and compared to age- and gender-matched controls.

RESULTS

Cerebellum and anterior lobe MRI volumetry were performed in 20 patients and nine controls. Mean anterior lobe and cerebellar volume were not statistically different. Three patients (15%), however, had an abnormal anterior lobe and cerebellar volume index (values outside 2.5 standard deviations). One of them also had a specific atrophy of the anterior lobe. All these patients had infectious or dysimmune associated SN.

CONCLUSION

Cerebellar atrophy is infrequently associated with SN, but can be found in some patients with SN related to infectious or immune mediated conditions. It can be more prominent in the anterior lobe and may contribute to the ataxia seen in these patients.

Magnetic resonance and nuclear medicine imaging in ataxias

Imaging techniques including computed tomography (CT), magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and positron emission tomography (PET) have been widely applied to the investigation of patients with acute or chronic ataxias. Fundamentally, CT has a role in the emergency evaluation of the patient with acute ataxia to ascertain brainstem or cerebellar hemorrhage and to exclude a mass lesion in the posterior cranial fossa. Conventional MRI is the most frequently performed imaging investigation in patients with ataxia. It can support the diagnosis of acute cerebellitis and Wernicke encephalopathy by revealing T2 signal changes with a typical distribution. In patients with inherited or sporadic chronic ataxia it reveals three fundamental patterns of atrophy of the brainstem, cerebellum, and spinal cord which match the gross neuropathological descriptions. These are represented by olivopontocerebellar atrophy (OPCA), cortical cerebellar atrophy (CCA), and spinal atrophy (SA). A substantial correspondence exists among these patterns of atrophy shown by MRI and the etiological classification of inherited or acquired chronic ataxias. This, along with demonstration of T2 signal changes characteristic of some diseases, makes conventional MRI potentially useful for the diagnostic work-up of the single patient, especially in the case of a sporadic disease. Non-conventional MR techniques including diffusion MR, spectroscopy, and functional MR have been used in patients with acute or chronic ataxia, but their exact role in the evaluation of the single patient is not established yet. They are currently investigated as potential tools to monitor progression of neurodegeneration in chronic ataxia and to serve as "surrogate markers" in clinical trials. Several radiotracers have been utilized in combination with SPECT and PET in patients with ataxia. Perfusion SPECT can reveal cerebellar blood flow abnormalities early in the course of cerebellitis. It has also been utilized to investigate perfusion of the brain in several inherited or sporadic chronic ataxic diseases, contributing to improved understanding of the pathophysiology of these conditions. Recently, perfusion SPECT has been tested as a "surrogate marker" to verify the effects of newly developed therapies in patients with a variety of chronic ataxias. Whole-body FDG-PET is recommended in patients with suspected paraneoplastic cerebellar degeneration to detect the primary malignancy. Brain FDG-PET has provided important information on the pathophysiology of several acquired and inherited conditions. PET and SPECT with radiotracers able to assess the nigrostriatal system or the density of D2 dopamine receptors in the striatum are increasingly used in patients with adult-onset sporadic ataxia for the differential diagnosis between multiple system atrophy in which overt striatal abnormalities are found and idiopathic late-onset cerebellar ataxia in which no abnormality is detected.

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.

Transcranial sonography reveals cerebellar, nigral, and forebrain abnormalities in Friedreich's ataxia

BACKGROUND

Friedreich's ataxia (FA) is essentially characterized by degeneration of the dorsal root ganglia, the dorsal nuclei of Clarke, and the long spinal fiber tracts, yet there is accumulating evidence that neurodegeneration extends beyond these predilection sites. Transcranial sonography (TCS) has evolved as a valuable complementary neuroimaging tool in the assessment of neurodegenerative diseases due to its capacity to well depict structural changes and the accumulation of heavy metals. Its use for assessing cerebellar neurodegeneration, however, has not yet been investigated.Here we investigated whether TCS allows to assess particular features of cerebellar as well as midbrain and forebrain abnormalities in FA.

METHODS

Comprehensive TCS imaging of 34 FA patients and 34 age-matched healthy controls.

RESULTS

Hyperechogenicity of the dentate nucleus was very frequent in FA patients (85%) and could even be observed in patients with short disease duration, suggesting that dentate alterations are a common and probably early feature of FA. Substantia nigra was significantly hypoechogenic, possibly indicating regional changes in subcellular brain iron regulation. FA patients showed significantly enlarged 4th, 3rd, and lateral ventricles, thus corroborating earlier MRI and postmortem findings of substantial cerebellar and forebrain atrophy in FA.

CONCLUSIONS

TCS provides a quick-to-apply and inexpensive in vivo assessment of both cerebellar and noncerebellar abnormalities in FA, in particular highlighting dentate hyperechogenicity as a core feature. It might serve as a promising tool for imaging aspects of cerebellar neurodegeneration also in other neurodegenerative disorders.

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.

Brain diffusion-weighted imaging in Friedreich's ataxia

BACKGROUND

Friedreich ataxia (FRDA) is the commonest form of autosomal recessive ataxia. This study aimed to define the extent of the brain damage in FRDA patients and to identify in vivo markers of neurodegeneration, using diffusion-weighted imaging (DWI).

METHODS

We studied 27 FRDA patients and 21 healthy volunteers using a 1.5 T scanner. Axial DW images were obtained and mean diffusivity (MD) maps were generated. Region of interests (ROIs) included medulla, pons, inferior, middle and superior cerebellar peduncles (ICP, SCP, MCP), dentate nucleus, cerebellar white matter, thalamus, caudate, putamen, pallidus, pyramidal tracts at level of posterior limb of internal capsule (PLIC), optic radiations (OR), and corpus callosum. Histograms of MD were generated for all pixels in the whole cerebral hemispheres and infratentorial compartment. Disease severity was assessed by the International Cooperative Ataxia Rating Scale (ICARS).

RESULTS

FRDA patients had significantly higher MD values than controls in medulla (P < 0.001), ICP (P < 0.001), MCP (P < 0.01), SCP (P < 0.001), OR (P < 0.001), and at the level of the infratentorial structures such as brainstem (P < 0.01), cerebellar hemispheres (P < 0.01), and especially in the cerebellar vermis (P < 0.001). MD values were strongly correlated with disease duration and ICARS score.

DISCUSSION

Our results showed that DWI is a suitable non-invasive technique to quantify the extent of neurodegeneration in FRDA, that appears more extended than previously reported, showing a microstructural involvement of structures such as OR and MCP.

Current and emerging treatment options in the management of Friedreich ataxia

Friedreich ataxia (FRDA) is the most common autosomal recessive ataxia. Oxidative damage within the mitochondria seems to have a key role in the disease phenotype. Therefore, FRDA treatment options have been mostly directed at antioxidant protection against mitochondrial damage. Available evidence seems to suggest that patients with FRDA should be treated with idebenone, because it is well tolerated and may reduce cardiac hypertrophy and, at higher doses, also improve neurological function, but large controlled clinical trials are still needed. Alternatively, gene-based strategies for the treatment of FRDA may involve the development of small-molecules increasing frataxin gene transcription. Animal and human studies are strongly needed to assess whether any of the potential new treatment strategies, such as iron-chelating therapies or treatment with erythropoietin or histone deacetylase inhibitors and other gene-based strategies, may translate into an effective therapy for this devastating disorder. In this review, we try to provide an answer to some questions related to current and emerging treatment options in the management of FRDA.

(1)H MR spectroscopy in Friedreich's ataxia and ataxia with oculomotor apraxia type 2

BACKGROUND AND AIM

Friedreich's ataxia (FRDA) and ataxia with oculomotor apraxia type 2 (AOA2) are the two most frequent forms of autosomal recessive cerebellar ataxias. However, brain metabolism in these disorders is poorly characterized and biomarkers of the disease progression are lacking. We aimed at assessing the neurochemical profile of the pons, the cerebellar hemisphere and the vermis in patients with FRDA and AOA2 to identify potential biomarkers of these diseases.

METHODS

Short-echo, single-voxel proton ((1)H) magnetic resonance spectroscopy data were acquired from 8 volunteers with FRDA, 9 volunteers with AOA2, and 38 control volunteers at 4T. Disease severity was assessed by the Friedreich's Ataxia Rating Scale (FARS).

RESULTS

Neuronal loss/dysfunction was indicated in the cerebellar vermis and hemispheres in both diseases by lower total N-acetylaspartate levels than controls. The putative gliosis marker myo-inositol was higher than controls in the vermis and pons in AOA2 and in the vermis in FRDA. Total creatine, another potential gliosis marker, was higher in the cerebellar hemispheres in FRDA relative to controls. Higher glutamine in FRDA and lower glutamate in AOA2 than controls were observed in the vermis, indicating different mechanisms possibly leading to altered glutamatergic neurotransmission. In AOA2, total N-acetylaspartate levels in the cerebellum strongly correlated with the FARS score (p<0.01).

CONCLUSION

Distinct neurochemical patterns were observed in the two patient populations, warranting further studies with larger patient populations to determine if the alterations in metabolite levels observed here may be utilized to monitor disease progression and treatment.