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

Neuromagnetic responses to multimodal stimuli in Friedreich's ataxia

OBJECTIVE

This study explores the utility of various evoked fields in elucidating the pathophysiology of Friedreich's ataxia (FA) and potentially contributing to developing more targeted diagnostic and therapeutic strategies.

METHODS

Thirty-seven patients with FA aged 27.6 ± 7.4 years and a control group of 17 healthy subjects were enrolled in the study. The neuromagnetic response to auditory, tactile, visual, somatosensory, auditory and tactile oddball stimulation were acquired. For all the components of interest, latency and amplitude were measured and correlated with clinical data.

RESULTS

Neuromagnetic responses were identifiable in more than 90% of cases. A significant response delay was observed in all tested modalities (auditory, somatosensory, tactile and visual responses). P300 responses were comparable in patients and healthy subjects. Latencies of visual and auditory responses correlated with SARA scores. Moreover, latencies of auditory responses correlated with disease onset age, whereas latencies of visual responses correlated with disease severity.

CONCLUSIONS

Auditory and visual responses correlated with the severity of the disease, whereas alterations in somatosensory responses represent an intrinsic characteristic of the disease.

SIGNIFICANCE

In FA the study of evoked visual fields could provide a possible biomarker of disease progression and treatment efficacy.

Cognition in cerebellar disorders: What's in the profile? A systematic review and meta-analysis

OBJECTIVE

This systematic review and meta-analysis aim to examine the profile and extent of cognitive deficits in patients with cerebellar disorders, and to provide a complete overview of the cognitive domains that might be affected in the Cerebellar Cognitive Affective Syndrome (CCAS).

METHODS

MEDLINE, Embase, PsycINFO, and Web of Science were systematically searched to 17-07-2024. Studies were considered if the participants were adult patients with a clinical diagnosis of cerebellar disorder and were neuropsychological assessed. Outcomes were grouped into the domains of processing speed, language, social cognition, executive function, visuospatial skills, episodic memory, verbal intelligence, attention, and working memory. All aetiologies were included for first evaluation and patients were assigned to one of two groups (focal vs. degenerative) for secondary evaluation. Random-effects models were employed for the meta-analyses.

RESULTS

129 studies with a total of 3140 patients with cerebellar disorders were included. Patients performed significantly worse compared to control/standardized data in all domains. Deficits were most pronounced in processing speed, ES [95% CI] = - 0.83 [- 1.04, - 0.63], language, ES [95% CI] = - 0.81 [- 0.94, - 0.67], and social cognition, ES [95% CI] = - 0.81 [- 1.19, - 0.42]. Cognitive impairment varied between patients with focal cerebellar lesions and degenerative cerebellar disorders, but was overall worse in the degenerative group.

DISCUSSION

Cerebellar disorders can impact many cognitive domains, extending beyond executive functioning, visuospatial skills, and language. These outcomes contribute to a broader understanding of the cerebellum's role in cognition and sheds light on the cognitive deficits associated with cerebellar disorders.

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.

Subtypes of cognitive impairment in cerebellar disease identified by cross-diagnostic cluster-analysis: results from a German multicenter study

BACKGROUND

Cognitive and neuropsychiatric impairment, known as cerebellar cognitive affective syndrome (CCAS), may be present in cerebellar disorders. This study identified distinct CCAS subtypes in cerebellar patients using cluster analysis.

METHODS

The German CCAS-Scale (G-CCAS-S), a brief screening test for CCAS, was assessed in 205 cerebellar patients and 200 healthy controls. K-means cluster analysis was applied to G-CCAS-S data to identify cognitive clusters in patients. Demographic and clinical variables were used to characterize the clusters. Multiple linear regression quantified their relative contribution to cognitive performance. The ability of the G-CCAS-S to correctly distinguish between patients and controls was compared across the clusters.

RESULTS

Two clusters explained the variance of cognitive performance in patients' best. Cluster 1 (30%) exhibited severe impairment. Cluster 2 (70%) displayed milder dysfunction and overlapped substantially with that of healthy controls. Cluster 1 patients were on average older, less educated, showed more severe ataxia and more extracerebellar involvement than cluster 2 patients. The cluster assignment predicted cognitive performance even after adjusting for all other covariates. The G-CCAS-S demonstrated good discriminative ability for cluster 1, but not for cluster 2.

CONCLUSIONS

The variance of cognitive impairment in cerebellar disorders is best explained by one severely affected and one mildly affected cluster. Cognitive performance is not only predicted by demographic/clinical characteristics, but also by cluster assignment itself. This indicates that factors that have not been captured in this study likely have effects on cognitive cerebellar functions. Moreover, the CCAS-S appears to have a relative weakness in identifying patients with only mild cognitive deficits.

STUDY REGISTRATION

The study has prospectively been registered at the German Clinical Study Register ( https://www.drks.de ; DRKS-ID: DRKS00016854).

Oculomotor and Vestibular Deficits in Friedreich Ataxia - Systematic Review and Meta-Analysis of Quantitative Measurements

Disease-specific oculomotor assessments play a crucial role in the early diagnosis of hereditary cerebellar ataxias. Whereas several studies have reported on quantitative oculomotor and vestibular measurements in Friedreich's Ataxia (FRDA), the value of specific oculomotor paradigms remains unclear. We aimed to address this knowledge gap through a systematic literature review and providing disease-specific recommendations for a tailored set of eye-movement recordings in FRDA. MEDLINE and Embase were searched for studies reporting on quantitative oculomotor and/or vestibular measurements in FRDA-patients. Data on oculomotor and vestibular parameters were extracted and correlations with a range of clinical parameters were sought. Included studies (n = 17) reported on 185 patients. Abnormalities observed included the presence of saccadic intrusions (143/161) such as square-wave jerks (SWJ, 90/109) and ocular flutter (21/43), impaired eccentric gaze-holding (40/104), abnormal pursuit (81/93) and angular vestibulo-ocular reflex (aVOR) deficits (39/48). For visually-guided saccades (VGS), we frequently observed increases in saccade latency (27/38) and dysmetric saccades (71/93), whereas saccade velocity was more often preserved (37/43). Augmented anti-saccade (AS) latency, downbeat nystagmus and frequent macro-SWJ correlated with disease duration. Increased AS-latency and VGS-latency, frequent macro-SWJ, reduced aVOR-gain and augmented aVOR peak-latency correlated with disease severity. A broad range of oculomotor and vestibular deficits are documented in the literature. Impairments in pursuit, saccades and aVOR-responses are most commonly reported, and as such, should be prioritized as disease markers. Quantitative oculomotor testing in FRDA may facilitate early diagnosis and prove valuable in monitoring disease progression and treatment response.

The Role of Verbal Fluency in the Cerebellar Cognitive Affective Syndrome Scale in Friedreich Ataxia

Cerebellar pathology engenders the disturbance of movement that characterizes Friedreich ataxia (FRDA), yet the impact of cerebellar pathology on cognition in FRDA remains unclear. Numerous studies have unequivocally demonstrated the role of the cerebellar pathology in disturbed cognitive, language and affective regulation, referred to as Cerebellar Cognitive Affective Syndrome (CCAS), and quantified by the CCAS-Scale (CCAS-S). The presence of dysarthria in many individuals with ataxia, particularly FRDA, may confound results on some items of the CCAS-S resulting in false-positive scores. This study explored the relationship between performance on the CCAS-S and clinical metrics of disease severity in 57 adults with FRDA. In addition, this study explored the relationship between measures of intelligibility and naturalness of speech and scores on the CCAS-S in a subgroup of 39 individuals with FRDA. We demonstrated a significant relationship between clinical metrics and performance on the CCAS-S. In addition, we confirmed the items that returned the greatest rate of failure were based on Verbal Fluency Tasks, revealing a significant relationship between these items and measures of speech. Measures of speech explained over half of the variance in the CCAS-S score suggesting the role of dysarthria in the performance on the CCAS-S is not clear. Further work is required prior to adopting the CCAS-S as a cognitive screening tool for individuals with FRDA.

Anodal Cerebellar Transcranial Direct Current Stimulation Reduces Motor and Cognitive Symptoms in Friedreich's Ataxia: A Randomized, Sham-Controlled Trial

BACKGROUND

Friedreich Ataxia is the most common recessive ataxia with only one therapeutic drug approved solely in the United States.

OBJECTIVE

The aim of this work was to investigate whether anodal cerebellar transcranial direct current stimulation (ctDCS) reduces ataxic and cognitive symptoms in individuals with Friedreich's ataxia (FRDA) and to assess the effects of ctDCS on the activity of the secondary somatosensory (SII) cortex.

METHODS

We performed a single-blind, randomized, sham-controlled, crossover trial with anodal ctDCS (5 days/week for 1 week, 20 min/day, density current: 0.057 mA/cm2 ) in 24 patients with FRDA. Each patient underwent a clinical evaluation (Scale for the Assessment and Rating of Ataxia, composite cerebellar functional severity score, cerebellar cognitive affective syndrome scale) before and after anodal and sham ctDCS. Activity of the SII cortex contralateral to a tactile oddball stimulation of the right index finger was evaluated with brain functional magnetic resonance imaging at baseline and after anodal/sham ctDCS.

RESULTS

Anodal ctDCS led to a significant improvement in the Scale for the Assessment and Rating of Ataxia (-6.5%) and in the cerebellar cognitive affective syndrome scale (+11%) compared with sham ctDCS. It also led to a significant reduction in functional magnetic resonance imaging signal at the SII cortex contralateral to tactile stimulation (-26%) compared with sham ctDCS.

CONCLUSIONS

One week of treatment with anodal ctDCS reduces motor and cognitive symptoms in individuals with FRDA, likely by restoring the neocortical inhibition normally exerted by cerebellar structures. This study provides class I evidence that ctDCS stimulation is effective and safe in FRDA. © 2023 International Parkinson and Movement Disorder Society.

Auditory neuropathy in mice and humans with Friedreich ataxia

OBJECTIVE

Recent studies have found that human Friedreich ataxia patients have dysfunction of transmission in the auditory neural pathways. Here, we characterize hearing deficits in a mouse model of Friedreich ataxia and compare these to a clinical population.

METHODS

Sixteen mice with a C57BL/6 background were evaluated. Eight were YG8Pook/J animals (Friedreich ataxia phenotype) and eight wild-type mice served as controls. Auditory function was assessed between ages 6 and 12 months using otoacoustic emissions and auditory steady-state responses. At study end, motor deficit was assessed using Rotorod testing and inner ear tissue was examined. Thirty-seven individuals with Friedreich ataxia underwent auditory steady-state evoked potential assessment and response amplitudes were compared with functional hearing ability (speech perception-in-noise) and disease status was measured by the Friedreich Ataxia Rating Scale.

RESULTS

The YG8Pook/J mice showed anatomic and functional abnormality. While otoacoustic emission responses from the cochlear hair cells were mildly affected, auditory steady-state responses showed exaggerated amplitude reductions as the animals aged with Friedreich ataxia mice showing a 50-60% decrease compared to controls who showed only a 20-25% reduction (F(2,94)  = 17.90, p < 0.00). Furthermore, the YG8Pook/J mice had fewer surviving spiral ganglion neurons, indicating greater degeneration of the auditory nerve. Neuronal density was 20-25% lower depending on cochlear region (F(1, 30)  = 45.02, p < 0.001). In human participants, auditory steady-state response amplitudes were correlated with both Consonant-Nucleus-Consonant word scores and Friedreich Ataxia Rating Scale score.

INTERPRETATION

This study found degenerative changes in auditory structure and function in YG8Pook/J mice, indicating that auditory measures in these animals may provide a model for testing Friedreich ataxia treatments. In addition, auditory steady-state response findings in a clinical population suggested that these scalp-recorded potentials may serve as an objective biomarker for disease progress in affected individuals.

Reduced cerebello-cerebral functional connectivity correlates with disease severity and impaired white matter integrity in Friedreich ataxia

Friedreich ataxia (FRDA) is a rare, inherited neurodegenerative disease characterised in most cases by progressive and debilitating motor dysfunction. Degeneration of cerebellar white matter pathways have been previously reported, alongside indications of cerebello-cerebral functional alterations. In this work, we examine resting-state functional connectivity changes within cerebello-cerebral circuits, and their associations with disease severity (Scale for the Assessment and Rating of Ataxia [SARA]), psychomotor function (speeded and paced finger tapping), and white matter integrity (diffusion tensor imaging) in 35 adults with FRDA and 45 age and sex-matched controls. Voxel-wise seed-based functional connectivity was assessed for three cerebellar cortical regions (anterior lobe, lobules I-V; superior posterior lobe, lobules VI-VIIB; inferior posterior lobe, lobules VIIIA-IX) and two dentate nucleus seeds (dorsal and ventral). Compared to controls, people with FRDA showed significantly reduced connectivity between the anterior cerebellum and bilateral pre/postcentral gyri, and between the superior posterior cerebellum and left dorsolateral PFC. Greater disease severity correlated with lower connectivity in these circuits. Lower anterior cerebellum-motor cortex functional connectivity also correlated with slower speeded finger tapping and less fractional anisotropy in the superior cerebellar peduncles, internal capsule, and precentral white matter in the FRDA cohort. There were no significant between-group differences in inferior posterior cerebellar or dentate nucleus connectivity. This study indicates that altered cerebello-cerebral functional connectivity is associated with functional status and white matter damage in cerebellar efferent pathways in people with FRDA, particularly in motor circuits.

Determinant of the cerebellar cognitive affective syndrome in Friedreich's ataxia

BACKGROUND

Individuals with Friedreich's ataxia (FRDA) display significantly lower performances in many cognitive domains with a pattern of impairment that falls within the cerebellar cognitive affective syndrome (CCAS).

OBJECTIVE

To assess in a large cohort of individuals with FRDA, the main determinant of the CCAS using multiple variable regression models.

METHODS

This is a monocentric observational study that included 39 individuals with FRDA. Ataxic motor symptoms were evaluated with the SARA and cognitive functions with the CCAS-Scale (CCAS-S). Age, SARA, GAA1, Age of symptoms onset (ASO), Age and disease duration (DD) were chosen as covariates in a linear regression model to predict CCAS-S failed items and covariates in a logistic regression model to predict definite CCAS.

RESULTS

Patients mean age, SARA score, ASO, DD and GAA1 were respectively of 29 ± 14, 22 ± 10, 14 ± 11, 15 ± 9 and 712 ± 238 (4 point-mutations). Mean CCAS-S raw score was of 86 ± 16, mean number of failed items was 2.9 ± 1.6. Twenty-three individuals had definite CCAS. The multiple linear regression model with age, SARA, ASO, DD & GAA1 as covariates was statistically significant to predict CCAS-S failed items. The SARA was the only significant coefficient in regression models for predicting CCAS-S failed items number and the definite CCAS occurrence.

CONCLUSIONS

CCAS is highly prevalent in adult individuals with FRDA. CCAS is predicted by ataxic motor symptoms severity. This finding supports common core cerebellar pathophysiology in both cognitive and motor symptoms in FRDA and warrants screening for CCAS, especially in patients with SARA > 20.

Clinical management guidelines for Friedreich ataxia: best practice in rare diseases

BACKGROUND

Individuals with Friedreich ataxia (FRDA) can find it difficult to access specialized clinical care. To facilitate best practice in delivering healthcare for FRDA, clinical management guidelines (CMGs) were developed in 2014. However, the lack of high-certainty evidence and the inadequacy of accepted metrics to measure health status continues to present challenges in FRDA and other rare diseases. To overcome these challenges, the Grading of Recommendations Assessment and Evaluation (GRADE) framework for rare diseases developed by the RARE-Bestpractices Working Group was adopted to update the clinical guidelines for FRDA. This approach incorporates additional strategies to the GRADE framework to support the strength of recommendations, such as review of literature in similar conditions, the systematic collection of expert opinion and patient perceptions, and use of natural history data.

METHODS

A panel representing international clinical experts, stakeholders and consumer groups provided oversight to guideline development within the GRADE framework. Invited expert authors generated the Patient, Intervention, Comparison, Outcome (PICO) questions to guide the literature search (2014 to June 2020). Evidence profiles in tandem with feedback from individuals living with FRDA, natural history registry data and expert clinical observations contributed to the final recommendations. Authors also developed best practice statements for clinical care points that were considered self-evident or were not amenable to the GRADE process.

RESULTS

Seventy clinical experts contributed to fifteen topic-specific chapters with clinical recommendations and/or best practice statements. New topics since 2014 include emergency medicine, digital and assistive technologies and a stand-alone section on mental health. Evidence was evaluated according to GRADE criteria and 130 new recommendations and 95 best practice statements were generated.

DISCUSSION AND CONCLUSION

Evidence-based CMGs are required to ensure the best clinical care for people with FRDA. Adopting the GRADE rare-disease framework enabled the development of higher quality CMGs for FRDA and allows individual topics to be updated as new evidence emerges. While the primary goal of these guidelines is better outcomes for people living with FRDA, the process of developing the guidelines may also help inform the development of clinical guidelines in other rare diseases.