The cerebellum looks normal in Friedreich ataxia

Altered Intracerebellar Functional Connectivity in Friedreich's Ataxia: A Graph-Theory Functional MRI Study

Historically, Friedreich's Ataxia (FRDA) has been linked to a relatively preserved cerebellar cortex. Recent advances in neuroimaging have revealed altered cerebello-cerebral functional connectivity (FC), but the extent of intra-cerebellar FC changes and their impact on cognition remains unclear. This study investigates intra-cerebellar FC alterations and their cognitive implications in FRDA. In this cross-sectional, single-center study, resting-state functional MRI data from 17 patients with FRDA (average age 27.7 ± 13.6 years; F/M = 6/11) and 20 healthy controls (HC) (average age 29.4 ± 9.7 years; F/M = 9/11), all of whom underwent neuropsychological testing, were analyzed. From functional connectivity matrices, graph measures were computed at both the network and node levels using two complementary parcellations. FRDA patients exhibited decreased global efficiency (p = 0.04), nodal degree (p = 0.001) and betweenness centrality (p = 0.04) in the vermal portion of lobule VIII, along with reduced global efficiency in cerebellar regions belonging to the Control-A network (p = 0.02), one of the three subdivisions of the Frontoparietal network. Verbal memory deficits correlated with global efficiency in both the vermal portion of lobule VIII (r = 0.53, p = 0.02) and the cerebellar regions of the Control-A network (r = 0.49, p = 0.05). Graph analysis revealed regional intra-cerebellar FC changes in FRDA, marked by reduced functional centrality in cerebellar regions of the vermis and responsible for executive functions. These changes correlated with cognitive alterations, highlighting the role of the cerebellar cortex in the cognitive impairment observed in FRDA.

CHARON: An Imaging-Based Diagnostic Algorithm to Navigate Through the Sea of Hereditary Degenerative Ataxias

The complexity in diagnosing hereditary degenerative ataxias lies not only in their rarity, but also in the variety of different genetic conditions that can determine sometimes similar and overlapping clinical findings. In this light, Magnetic Resonance Imaging (MRI) plays a key role in the evaluation of these conditions, being a fundamental diagnostic tool needed not only to exclude other causes determining the observed clinical phenotype, but also to proper guide to an adequate genetic testing. Here, we propose an MRI-based diagnostic algorithm named CHARON (Characterization of Hereditary Ataxias Relying On Neuroimaging), to help in disentangling among the numerous, and apparently very similar, hereditary degenerative ataxias. Being conceived from a neuroradiological standpoint, it is based primarily on an accurate evaluation of the observed MRI findings, with the first and most important being the pattern of cerebellar atrophy. Along with the evaluation of the presence, or absence, of additional signal changes and/or supratentorial involvement, CHARON allows for the identification of a small groups of ataxias sharing similar imaging features. The integration of additional MRI findings, demographic, clinical and laboratory data allow then for the identification of typical, and in some cases pathognomonic, phenotypes of hereditary ataxias.

A patient with neuropathy and ataxia: what do I have to consider?

PURPOSE OF REVIEW

An increasing number of peripheral neuro(no)pathies are identified as involving other components of the neurological system, particularly those that further impair balance. Here we aim to outline an evidence-based approach to the diagnosis of patients who present with a somatosensory disorder which also involves at least one other area of neurological impairment such as the vestibular, auditory, or cerebellar systems.

RECENT FINDINGS

Detailed objective investigation of patients who present with sensory impairment, particularly where the degree of imbalance is greater than would be expected, aids the accurate diagnosis of genetic, autoimmune, metabolic, and toxic neurological disease.

SUMMARY

Diagnosis and management of complex somatosensory disorders benefit from investigation which extends beyond the presenting sensory impairment.

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.

Conventional MRI findings in hereditary degenerative ataxias: a pictorial review

Purpose

Cerebellar ataxias are a large and heterogeneous group of disorders. The evaluation of brain parenchyma via MRI plays a central role in the diagnostic assessment of these conditions, being mandatory to exclude the presence of other underlying causes in determining the clinical phenotype. Once these possible causes are ruled out, the diagnosis is usually researched in the wide range of hereditary or sporadic ataxias.

Methods

We here propose a review of the main clinical and conventional imaging findings of the most common hereditary degenerative ataxias, to help neuroradiologists in the evaluation of these patients.

Results

Hereditary degenerative ataxias are all usually characterized from a neuroimaging standpoint by the presence, in almost all cases, of cerebellar atrophy. Nevertheless, a proper assessment of imaging data, extending beyond the mere evaluation of cerebellar atrophy, evaluating also the pattern of volume loss as well as concomitant MRI signs, is crucial to achieve a proper diagnosis.

Conclusion

The integration of typical neuroradiological characteristics, along with patient’s clinical history and laboratory data, could allow the neuroradiologist to identify some conditions and exclude others, addressing the neurologist to the more appropriate genetic testing.

Pattern of Cerebellar Atrophy in Friedreich's Ataxia-Using the SUIT Template

Whole-brain voxel-based morphometry (VBM) studies revealed patterns of patchy atrophy within the cerebellum of Friedreich's ataxia patients, missing clear clinico-anatomic correlations. Studies so far are lacking an appropriate registration to the infratentorial space. To circumvent these limitations, we applied a high-resolution atlas template of the human cerebellum and brainstem (SUIT template) to characterize regional cerebellar atrophy in Friedreich's ataxia (FRDA) on 3-T MRI data. We used a spatially unbiased voxel-based morphometry approach together with T2-based manual segmentation, T2 histogram analysis, and atlas generation of the dentate nuclei in a representative cohort of 18 FRDA patients and matched healthy controls. We demonstrate that the cerebellar volume in FRDA is generally not significantly different from healthy controls but mild lobular atrophy develops beyond normal aging. The medial parts of lobule VI, housing the somatotopic representation of tongue and lips, are the major site of this lobular atrophy, which possibly reflects speech impairment. Extended white matter affection correlates with disease severity across and beyond the cerebellar inflow and outflow tracts. The dentate nucleus, as a major site of cerebellar degeneration, shows a mean volume loss of about 30%. Remarkably, not the atrophy but the T2 signal decrease of the dentate nuclei highly correlates with disease duration and severity.

Cerebellum and cognition in Friedreich ataxia: a voxel-based morphometry and volumetric MRI study

BACKGROUND

Recent studies have suggested the presence of a significant atrophy affecting the cerebellar cortex in Friedreich ataxia (FRDA) patients, an area of the brain long considered to be relatively spared by neurodegenerative phenomena. Cognitive deficits, which occur in FRDA patients, have been associated with cerebellar volume loss in other conditions. The aim of this study was to investigate the correlation between cerebellar volume and cognition in FRDA.

METHODS

Nineteen FRDA patients and 20 healthy controls (HC) were included in this study and evaluated via a neuropsychological examination. Cerebellar global and lobular volumes were computed using the Spatially Unbiased Infratentorial Toolbox (SUIT). Furthermore, a cerebellar voxel-based morphometry (VBM) analysis was also carried out. Correlations between MRI metrics and clinical data were tested via partial correlation analysis.

RESULTS

FRDA patients showed a significant reduction of the total cerebellar volume (p = 0.004), significantly affecting the Lobule IX (p = 0.001). At the VBM analysis, we found a cluster of significant reduced GM density encompassing the entire lobule IX (p = 0.003). When correlations were probed, we found a direct correlation between Lobule IX volume and impaired visuo-spatial functions (r = 0.58, p = 0.02), with a similar correlation that was found between the same altered function and results obtained at the VBM (r = 0.52; p = 0.03).

CONCLUSIONS

With two different image analysis techniques, we confirmed the presence of cerebellar volume loss in FRDA, mainly affecting the posterior lobe. In particular, Lobule IX atrophy correlated with worse visuo-spatial abilities, further expanding our knowledge about the physiopathology of cognitive impairment in FRDA.

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.

Plasma Markers of Neurodegeneration Are Raised in Friedreich's Ataxia

Background: Friedreich's ataxia (FRDA) is the most common autosomal recessive ataxia. Disease-modifying treatments are not available yet; however, several compounds are currently under investigation. As a result, there is a growing need for the identification of robust and easily accessible biomarkers for the monitoring of disease activity and therapeutic efficacy. The simultaneous measurement of multiple brain-derived proteins could represent a time- and cost-efficient approach for biomarker investigation in pathologically complex neurodegenerative diseases like FRDA. Objectives: To investigate the role of plasma neurofilament-light chain (NfL), glial fibrillary acidic protein (GFAP), total tau (t-tau) and ubiquitin C-terminal hydrolase L1(UCHL1) as biomarkers in FRDA. Additionally, NfL measurements derived from the novel multiplex assay were compared to those from an established NfL singleplex assay. Methods: In this study, an ultrasensitive Single molecule array (Simoa) 4-plex assay was used for the measurement of plasma NfL, GFAP, t-tau, and UCHL1 in 33 FRDA patients and 13 age-matched controls. Differences in biomarker concentrations between these groups were computed and associations with genetic and disease related parameters investigated. Additionally, the agreement between NfL measurements derived from the 4-Plex and an established Simoa NfL singleplex assay was assessed. Results: Mean plasma NfL, GFAP and UCHL1 levels were significantly higher in FRDA patients than in controls (NfL: p < 0.001; GFAP: p = 0.006, and UCHL1: p = 0.020). Conversely, there was no significant difference in concentrations of t-tau in the patient and control group (p = 0.236). None of the proteins correlated with the GAA repeat length or the employed measures of disease severity. The individual NfL values derived from the two assays showed a strong concordance (r_c = 0.93). Although the mean difference of 1.29 pg/mL differed significantly from 0 (p = 0.006), regression analysis did not indicate the presence of a proportional bias. Conclusion: This is the first study demonstrating that NfL, GFAP, and UCHL1 levels are raised in FRDA, potentially reflecting ongoing neuronal degeneration and glial activation. Further studies are required to determine their role as marker for disease activity and progression. Furthermore, the novel 4-plex assay appears to be a valid tool to simultaneously measure brain-derived proteins at extremely low concentrations in the peripheral circulation.

Cerebellar Ataxia in Children: A Clinical and MRI Approach to the Differential Diagnosis

: The cerebellum has long been recognized as a fundamental structure in motor coordination. Structural cerebellar abnormalities and diseases involving the cerebellum are relatively common in children. The not always specific clinical presentation of ataxia, incoordination, and balance impairment can often be a challenge to attain a precise diagnosis. Continuous advances in genetic research and moreover the constant development in neuroimaging modalities, particularly in the field of magnetic resonance imaging, have promoted a better understanding of cerebellar diseases and led to several modifications in their classification in recent years. Thorough clinical and neuroimaging investigation is recommended for proper diagnosis. This review outlines an update of causes of cerebellar disorders that present clinically with ataxia in the pediatric population. These conditions were classified in 2 major groups, namely genetic malformations and acquired or disruptive disorders recognizable by neuroimaging and subsequently according to their features during the prenatal and postnatal periods.

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.

Cerebellum and neurodegenerative diseases: Beyond conventional magnetic resonance imaging

The cerebellum plays a key role in movement control and in cognition and cerebellar involvement is described in several neurodegenerative diseases. While conventional magnetic resonance imaging (MRI) is widely used for brain and cerebellar morphologic evaluation, advanced MRI techniques allow the investigation of cerebellar microstructural and functional characteristics. Volumetry, voxel-based morphometry, diffusion MRI based fiber tractography, resting state and task related functional MRI, perfusion, and proton MR spectroscopy are among the most common techniques applied to the study of cerebellum. In the present review, after providing a brief description of each technique’s advantages and limitations, we focus on their application to the study of cerebellar injury in major neurodegenerative diseases, such as multiple sclerosis, Parkinson’s and Alzheimer’s disease and hereditary ataxia. A brief introduction to the pathological substrate of cerebellar involvement is provided for each disease, followed by the review of MRI studies exploring structural and functional cerebellar abnormalities and by a discussion of the clinical relevance of MRI measures of cerebellar damage in terms of both clinical status and cognitive performance.

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.

Friedreich Ataxia: current status and future prospects

Friedreich ataxia (FA) represents the most frequent type of inherited ataxia. Most patients carry homozygous GAA expansions in the first intron of the frataxin gene on chromosome 9. Due to epigenetic alterations, frataxin expression is significantly reduced. Frataxin is a mitochondrial protein. Its deficiency leads to mitochondrial iron overload, defective energy supply and generation of reactive oxygen species. This review gives an overview over clinical and genetic aspects of FA and discusses current concepts of frataxin biogenesis and function as well as new therapeutic strategies.

Milestones in Friedreich ataxia: more than a century and still learning

Friedreich ataxia (FRDA) is the most common autosomal recessive ataxia worldwide. This review highlights the main clinical features, pathophysiological mechanisms, and therapeutic approaches for FRDA patients. The disease is characterized by a combination of neurological involvement (ataxia and neuropathy), cardiomyopathy, skeletal abnormalities, and glucose metabolism disturbances. FRDA is caused by expanded guanine-adenine-adenine (GAA) triplet repeats in the first intron of the frataxin gene (FXN), resulting in reduction of messenger RNA and protein levels of frataxin in different tissues. The molecular and metabolic disturbances, including iron accumulation, lead to pathological changes characterized by spinal cord and dorsal root ganglia atrophy, dentate nucleus atrophy without global cerebellar volume reduction, and hypertrophic cardiomyopathy. DNA analysis is the hallmark for the diagnosis of FRDA. There is no specific treatment to stop the disease progression in FRDA patients. However, a number of drugs are under investigation. Therapeutic approaches intend to improve mitochondrial functioning and to increase FXN expression.