In children with Friedreich ataxia, muscle and ataxia parameters are associated

Skeletal Muscle Involvement in Friedreich Ataxia

Friedreich Ataxia (FRDA) is an inherited neuromuscular disorder triggered by a deficit of the mitochondrial protein frataxin. At a cellular level, frataxin deficiency results in insufficient iron-sulfur cluster biosynthesis and impaired mitochondrial function and adenosine triphosphate production. The main clinical manifestation is a progressive balance and coordination disorder which depends on the involvement of peripheral and central sensory pathways as well as of the cerebellum. Besides the neurological involvement, FRDA affects also the striated muscles. The most prominent manifestation is a hypertrophic cardiomyopathy, which also represents the major determinant of premature mortality. Moreover, FRDA displays skeletal muscle involvement, which contributes to the weakness and marked fatigue evident throughout the course of the disease. Herein, we review skeletal muscle findings in FRDA generated by functional imaging, histology, as well as multiomics techniques in both disease models and in patients. Altogether, these findings corroborate a disease phenotype in skeletal muscle and support the notion of progressive mitochondrial damage as a driver of disease progression in FRDA. Furthermore, we highlight the relevance of skeletal muscle investigations in the development of biomarkers for early-phase trials and future therapeutic strategies in FRDA.

Effectiveness of rehabilitation intervention in persons with Friedreich ataxia

Introduction

The relevance of rehabilitation in progressive neurological disorders, such as Friedreich's Ataxia (FRDA), has yet to be convincingly proven. FRDA is characterized by ataxia, loss of gait, scoliosis, cardiomyopathy, dysarthria and dysphagia, with reduced life expectancy. The disease onset is usually in adolescence, leading to progressive disability. Omaveloxolone has been recently approved as the first pharmacological treatment for FRDA in adults and adolescents aged 16 years and older. Regarding non-pharmacological therapies, neurorehabilitation is a valuable aid in addressing the symptoms and in maintaining the residual functioning. We performed a prospective observational cohort study to evaluate the efficacy of inpatient rehabilitation (IR) for people with FRDA.

Methods

A total of 42 individuals (29 adults and 13 children) with FRDA were recruited. There were 27 ambulant and 15 non-ambulant participants. The patients underwent IR of 3 and 4 weeks in children and adults, respectively. The IR treatment was designed to be applied within a multidisciplinary setting, so FRDA patients underwent, in addition to physiotherapy, also occupational therapy, practical manual activities and psychological support aiming to enhance transferable skills useful in the activities of daily living. The primary outcome was the Scale for the Assessment and Rating of Ataxia (SARA). Other measures were: Friedreich Ataxia Rating Scale (FARS) and Nine Hole Peg Test (NHPT). Furthermore, we used the 6 Minute Walk Test (6MWT), the Timed Up and Go (TUG) and the Berg Balance Scale (BBS) only on ambulant subjects. Outcomes were evaluated at baseline and at the end of the treatment.

Results

We report that the IR significantly improves motor performance and ataxia symptoms in patients with FRDA. Our study shows significant functional improvement in all the outcome measures used, except for NHPT bilaterally. FARS and SARA scores post-IR are significatively reduced when compared (p < 0.001).

Discussion

We demonstrate that IR programs in FRDA can provide a meaningful clinical improvement in terms of outcome measures. These findings could be useful when approaching progressive neurological disorders.

Skeletal muscle proteome analysis underpins multifaceted mitochondrial dysfunction in Friedreich's ataxia

Friedreich's ataxia (FRDA) is a severe multisystemic disorder caused by a deficiency of the mitochondrial protein frataxin. While some aspects of FRDA pathology are developmental, the causes underlying the steady progression are unclear. The inaccessibility of key affected tissues to sampling is a main hurdle. Skeletal muscle displays a disease phenotype and may be sampled in vivo to address open questions on FRDA pathophysiology. Thus, we performed a quantitative mass spectrometry-based proteomics analysis in gastrocnemius skeletal muscle biopsies from genetically confirmed FRDA patients (n = 5) and controls. Obtained data files were processed using Proteome Discoverer and searched by Sequest HT engine against a UniProt human reference proteome database. Comparing skeletal muscle proteomics profiles between FRDA and controls, we identified 228 significant differentially expressed (DE) proteins, of which 227 were downregulated in FRDA. Principal component analysis showed a clear separation between FRDA and control samples. Interactome analysis revealed clustering of DE proteins in oxidative phosphorylation, ribosomal elements, mitochondrial architecture control, and fission/fusion pathways. DE findings in the muscle-specific proteomics suggested a shift toward fast-twitching glycolytic fibers. Notably, most DE proteins (169/228, 74%) are target of the transcription factor nuclear factor-erythroid 2. Our data corroborate a mitochondrial biosignature of FRDA, which extends beyond a mere oxidative phosphorylation failure. Skeletal muscle proteomics highlighted a derangement of mitochondrial architecture and maintenance pathways and a likely adaptive metabolic shift of contractile proteins. The present findings are relevant for the design of future therapeutic strategies and highlight the value of skeletal muscle-omics as disease state readout in FRDA.

Applicability of quantitative oculomotor and SARA assessment in children

BACKGROUND

In clinical practice, eye movements can provide an early diagnostic marker for early onset ataxia (EOA). However, quantitative oculomotor assessment is not included in the most frequently used and age-validated ataxia rating scale in children, the Scale for the Assessment and Rating of Ataxia (SARA). We aimed to investigate the applicability of semi-quantitative eye movement assessment by the International Cooperative Ataxia Rating Scale (ICARS_OCM) and Ocular Motion Score (OMS_7-10) complementary to SARA measurements in children.

METHODS

In 52 typically developing children (aged 4-16 years; n = 4 per year of age), three independent assessors scored saccadic eye movements and ocular pursuit according to the ICARS_OCM and matching parameters from the OMS_7-10. For ICARS_OCM, we determined 1) construct validity for coordinated eye movements by correlation with OMS_7-10, ICARS_{EYE-HAND-COORDINATION} and SARA subscale scores, 2) agreement percentage and inter-rater agreement (Fleiss Kappa) and 3) age-dependency.

RESULTS

Spearman's rank correlations of ICARS_OCM with OMS_7-10 and ICARS- and SARA subscales were moderate to fair (all p < .001). Inter-rater agreement of ICARS-_OCM was 80.8%; (Fleiss Kappa: 0.411). ICARS_OCM scores revealed a similar exponentially decreasing association with age as the other SARA (sub)scores, reaching a plateau at 10 years of age.

INTERPRETATION

ICARS_OCM has a valid construct for the measurement of coordinated eye movement performance and is reliably assessable in children. ICARS_OCM reveals a similar age-dependent relationship as the other ataxia subscales, reflecting the physiological maturation of the cerebellum. In children, these data may implicate that ICARS_OCM can reliably contribute to coordination assessment, complementary to the SARA subscales.

Dimethyl fumarate dose-dependently increases mitochondrial gene expression and function in muscle and brain of Friedreich's ataxia model mice

Previously we showed that dimethyl fumarate (DMF) dose-dependently increased mitochondrial gene expression and function in cells and might be considered as a therapeutic for inherited mitochondrial disease, including Friedreich's ataxia (FA). Here we tested DMF's ability to dose-dependently increase mitochondrial function, mitochondrial gene expression (frataxin and cytochrome oxidase protein) and mitochondrial copy number in C57BL6 wild-type mice and the FXNKD mouse model of FA. We first dosed DMF at 0-320 mg/kg in C57BL6 mice and observed significant toxicity above 160 mg/kg orally, defining the maximum tolerated dose. Oral dosing of C57BL6 mice in the range 0-160 mg/kg identified a maximum increase in aconitase activity and mitochondrial gene expression in brain and quadriceps at 110 mg/kg DMF, thus defining the maximum effective dose (MED). The MED of DMF in mice overlaps the currently approved human-equivalent doses of DMF prescribed for multiple sclerosis (480 mg/day) and psoriasis (720 mg/day). In the FXNKD mouse model of FA, which has a doxycycline-induced deficit of frataxin protein, we observed significant decreases of multiple mitochondrial parameters, including deficits in brain mitochondrial Complex 2, Complex 4 and aconitase activity, supporting the idea that frataxin deficiency reduces mitochondrial gene expression, mitochondrial functions and biogenesis. About 110 mg/kg of oral DMF rescued these enzyme activities in brain and rescued frataxin and cytochrome oxidase expression in brain, cerebellum and quadriceps muscle of the FXNKD mouse model. Taken together, these results support the idea of using fumarate-based molecules to treat FA or other mitochondrial diseases.

Development of muscle ultrasound density in healthy fetuses and infants

Muscle ultrasound density (MUD) is a non-invasive parameter to indicate neuromuscular integrity in both children and adults. In healthy fetuses and infants, physiologic MUD values during development are still lacking. We therefore aimed to determine the physiologic, age-related MUD trend of biceps, quadriceps, tibialis anterior, hamstrings, gluteal and calf muscles, from pre- to the first year of postnatal life. To avoid a bias by pregnancy-related signal disturbances, we expressed fetal MUD as a ratio against bone ultrasound density. We used the full-term prenatal MUD ratio and the newborn postnatal MUD value as reference points, so that MUD development could be quantified from early pre- into postnatal life. Results: During the prenatal period, the total muscle group revealed a developmental MUD trend concerning a fetal increase in MUD-ratio from the 2nd trimester up to the end of the 3rd trimester [median increase: 27% (range 16-45), p < .001]. After birth, MUD-values increased up to the sixth month [median increase: 11% (range -7-27), p = 0.025] and stabilized thereafter. Additionally, there were also individual MUD characteristics per muscle group and developmental stage, such as relatively low MUD values of fetal hamstrings and high values of the paediatric gluteus muscles. These MUD trends are likely to concur with analogous developmentally, maturation-related alterations in the muscle water to peptide content ratios.

A clinical diagnostic algorithm for early onset cerebellar ataxia

Early onset cerebellar Ataxia (EOAc) comprises a large group of rare heterogeneous disorders. Determination of the underlying etiology can be difficult given the broad differential diagnosis and the complexity of the genotype-phenotype relationships. This may change the diagnostic work-up into a time-consuming, costly and not always rewarding task. In this overview, the Childhood Ataxia and Cerebellar Group of the European Pediatric Neurology Society (CACG-EPNS) presents a diagnostic algorithm for EOAc patients. In seven consecutive steps, the algorithm leads the clinician through the diagnostic process, including EOA identification, application of the Inventory of Non-Ataxic Signs (INAS), consideration of the family history, neuro-imaging, laboratory investigations, genetic testing by array CGH and Next Generation Sequencing (NGS). In children with EOAc, this algorithm is intended to contribute to the diagnostic process and to allow uniform data entry in EOAc databases.

Scales for the clinical evaluation of cerebellar disorders

Clinical scales represent an important tool not only for the initial grading/scoring of disease and assessment of progression, but also for the quantification of therapeutic effects in clinical trials. There are several scales available for the clinical evaluation of cerebellar symptoms. While some scales have been developed and evaluated for specific cerebellar disorders such as Friedreich ataxia, others reliably capture cerebellar symptoms with no respect to the underlying etiology. Each scale has its strengths and weaknesses. Extensive scales are certainly useful for thorough documentation of specific features of certain phenotypes, but this gain of information is not always essential for the purpose of a study. Therefore, compact and manageable scales like the Scale for the Assessment and Rating of Ataxia (SARA) or Brief Ataxia Rating Scale (BARS) are often preferred compared to more complex scales in observational and therapeutic studies.

Construct Validity and Reliability of the SARA Gait and Posture Sub-scale in Early Onset Ataxia

Aim: In children, gait and posture assessment provides a crucial marker for the early characterization, surveillance and treatment evaluation of early onset ataxia (EOA). For reliable data entry of studies targeting at gait and posture improvement, uniform quantitative biomarkers are necessary. Until now, the pediatric test construct of gait and posture scores of the Scale for Assessment and Rating of Ataxia sub-scale (SARA) is still unclear. In the present study, we aimed to validate the construct validity and reliability of the pediatric (SARA_GAIT/POSTURE) sub-scale. Methods: We included 28 EOA patients [15.5 (6-34) years; median (range)]. For inter-observer reliability, we determined the ICC on EOA SARA_GAIT/POSTURE sub-scores by three independent pediatric neurologists. For convergent validity, we associated SARA_GAIT/POSTURE sub-scores with: (1) Ataxic gait Severity Measurement by Klockgether (ASMK; dynamic balance), (2) Pediatric Balance Scale (PBS; static balance), (3) Gross Motor Function Classification Scale -extended and revised version (GMFCS-E&R), (4) SARA-kinetic scores (SARA_KINETIC; kinetic function of the upper and lower limbs), (5) Archimedes Spiral (AS; kinetic function of the upper limbs), and (6) total SARA scores (SARA_TOTAL; i.e., summed SARA_GAIT/POSTURE, SARA_KINETIC, and SARA_SPEECH sub-scores). For discriminant validity, we investigated whether EOA co-morbidity factors (myopathy and myoclonus) could influence SARA_GAIT/POSTURE sub-scores. Results: The inter-observer agreement (ICC) on EOA SARA_GAIT/POSTURE sub-scores was high (0.97). SARA_GAIT/POSTURE was strongly correlated with the other ataxia and functional scales [ASMK (r_s = -0.819; p < 0.001); PBS (r_s = -0.943; p < 0.001); GMFCS-E&R (r_s = -0.862; p < 0.001); SARA_KINETIC (r_s = 0.726; p < 0.001); AS (r_s = 0.609; p = 0.002); and SARA_TOTAL (r_s = 0.935; p < 0.001)]. Comorbid myopathy influenced SARA_GAIT/POSTURE scores by concurrent muscle weakness, whereas comorbid myoclonus predominantly influenced SARA_KINETIC scores. Conclusion: In young EOA patients, separate SARA_GAIT/POSTURE parameters reveal a good inter-observer agreement and convergent validity, implicating the reliability of the scale. In perspective of incomplete discriminant validity, it is advisable to interpret SARA_GAIT/POSTURE scores for comorbid muscle weakness.

Can rehabilitation improve the health and well-being in Friedreich's ataxia: a randomized controlled trial?

OBJECTIVE

To determine the effectiveness of a six-week rehabilitation programme followed by a home exercise programme for Friedreich's ataxia.

DESIGN

Randomized, delayed-start control single-blind trial.

SETTING

Outpatient rehabilitation centre.

SUBJECTS

Ambulant or non-ambulant individuals with Friedreich's ataxia.

INTERVENTION

Participants were randomized to a six-week outpatient rehabilitation programme, immediately (intervention group) or after a six-week delayed-start (control group). The rehabilitation was followed by a six-week home exercise programme.

MAIN MEASURES

The primary outcome was the Functional Independence Measure. Other measures included the Friedreich Ataxia Impact Scale and the Friedreich Ataxia Rating Scale. Outcomes were administered at baseline, 6, 12 and 18 weeks.

RESULTS

Of 159 individuals screened, 92 were excluded and 48 declined to participate. A total of 19 participants were enrolled in the study. There was no significant difference in Functional Independence Measure change from baseline to six weeks in the intervention group (mean ± standard deviation, 2.00 ± 3.16) as compared to the control group (0.56 ± 4.06). Change in the Friedreich Ataxia Impact Scale body movement subscale indicated a significant improvement in health and well-being in the intervention group compared to the control group ( P = 0.003). Significant within-group improvements in the Friedreich Ataxia Impact Scale and the motor domain of the Functional Independence Measure post-rehabilitation were not sustained post-home exercise programme.

CONCLUSION

Our study indicates that rehabilitation can improve health and well-being in individuals with Friedreich's ataxia; however, a larger study is required to have sufficient power to detect a significant change in the most sensitive measure of function, the motor domain of the Functional Independence Measure.

Reliability and discriminant validity of ataxia rating scales in early onset ataxia

AIM

To determine whether ataxia rating scales are reliable disease biomarkers for early onset ataxia (EOA).

METHOD

In 40 patients clinically identified with EOA (28 males, 12 females; mean age 15y 3mo [range 5-34y]), we determined interobserver and intraobserver agreement (interclass correlation coefficient [ICC]) and discriminant validity of ataxia rating scales (International Cooperative Ataxia Rating Scale [ICARS], Scale for Assessment and Rating of Ataxia [SARA], and Brief Ataxia Rating Scale [BARS]). Three paediatric neurologists independently scored ICARS, SARA and BARS performances recorded on video, and also phenotyped the primary and secondary movement disorder features. When ataxia was the primary movement disorder feature, we assigned patients to the subgroup 'EOA with core ataxia' (n=26). When ataxia concurred with other prevailing movement disorders (such as dystonia, myoclonus, and chorea), we assigned patients to the subgroup 'EOA with comorbid ataxia' (n=12).

RESULTS

ICC values were similar in both EOA subgroups of 'core' and 'comorbid' ataxia (0.92-0.99; ICARS, SARA, and BARS). Independent of the phenotype, the severity of the prevailing movement disorder predicted the ataxia rating scale scores (β=0.83-0.88; p<0.05).

INTERPRETATION

In patients with EOA, the reliability of ataxia rating scales is high. However, the discriminative validity for 'ataxia' is low. For adequate interpretation of ataxia rating scale scores, application in uniform movement disorder phenotypes is essential.

Automatic classification of gait in children with early-onset ataxia or developmental coordination disorder and controls using inertial sensors

Early-Onset Ataxia (EOA) and Developmental Coordination Disorder (DCD) are two conditions that affect coordination in children. Phenotypic identification of impaired coordination plays an important role in their diagnosis. Gait is one of the tests included in rating scales that can be used to assess motor coordination. A practical problem is that the resemblance between EOA and DCD symptoms can hamper their diagnosis. In this study we employed inertial sensors and a supervised classifier to obtain an automatic classification of the condition of participants. Data from shank and waist mounted inertial measurement units were used to extract features during gait in children diagnosed with EOA or DCD and age-matched controls. We defined a set of features from the recorded signals and we obtained the optimal features for classification using a backward sequential approach. We correctly classified 80.0%, 85.7%, and 70.0% of the control, DCD and EOA children, respectively. Overall, the automatic classifier correctly classified 78.4% of the participants, which is slightly better than the phenotypic assessment of gait by two pediatric neurologists (73.0%). These results demonstrate that automatic classification employing signals from inertial sensors obtained during gait maybe used as a support tool in the differential diagnosis of EOA and DCD. Furthermore, future extension of the classifier's test domains may help to further improve the diagnostic accuracy of pediatric coordination impairment. In this sense, this study may provide a first step towards incorporating a clinically objective and viable biomarker for identification of EOA and DCD.

Muscle Ultrasound in Patients with Glycogen Storage Disease Types I and III

In glycogen storage diseases (GSDs), improved longevity has resulted in the need for neuromuscular surveillance. In 12 children and 14 adults with the "hepatic" (GSD-I) and "myopathic" (GSD-III) phenotypes, we cross-sectionally assessed muscle ultrasound density (MUD) and muscle force. Children with both "hepatic" and "myopathic" GSD phenotypes had elevated MUD values (MUD Z-scores: GSD-I > 2.5 SD vs. GSD-III > 1 SD, p < 0.05) and muscle weakness (GSD-I muscle force; p < 0.05) of myopathic distribution. In "hepatic" GSD-I adults, MUD stabilized (GSD-I adults vs. GSD-I children, not significant), concurring with moderate muscle weakness (GSD-I adults vs. healthy matched pairs, p < 0.05). In "myopathic" GSD-III adults, MUD increased with age (MUD-GSD III vs. age: r = 0.71-0.83, GSD-III adults > GSD-III children, p < 0.05), concurring with pronounced muscle weakness (GSD-III adults vs. GSD-I adults, p < 0.05) of myopathic distribution. Children with "hepatic" and "myopathic" GSD phenotypes were both found to have myopathy. Myopathy stabilizes in "hepatic" GSD-I adults, whereas it progresses in "myopathic" GSD-III adults. Muscle ultrasonography provides an excellent, non-invasive tool for neuromuscular surveillance per GSD phenotype.

Phosphomannomutase deficiency (PMM2-CDG): ataxia and cerebellar assessment

BACKGROUND

Phosphomannomutase deficiency (PMM2-CDG) is the most frequent congenital disorder of glycosylation. The cerebellum is nearly always affected in PMM2-CDG patients, a cerebellar atrophy progression is observed, and cerebellar dysfunction is their main daily functional limitation. Different therapeutic agents are under development, and clinical evaluation of drug candidates will require a standardized score of cerebellar dysfunction. We aim to assess the validity of the International Cooperative Ataxia Rating Scale (ICARS) in children and adolescents with genetically confirmed PMM2-CDG deficiency. We compare ICARS results with the Nijmegen Pediatric CDG Rating Scale (NPCRS), neuroimaging, intelligence quotient (IQ) and molecular data.

METHODS

Our observational study included 13 PMM2-CDG patients and 21 control subjects. Ethical permissions and informed consents were obtained. Three independent child neurologists rated PMM2-CDG patients and control subjects using the ICARS. A single clinician administered the NPCRS. All patients underwent brain MRI, and the relative diameter of the midsagittal vermis was measured. Psychometric evaluations were available in six patients. The Mann-Whitney U test was used to compare ICARS between patients and controls. To evaluate inter-observer agreement in patients' ICARS ratings, intraclass correlation coefficients (ICC) were calculated. ICARS internal consistency was evaluated using Cronbach's alpha. Spearman's rank correlation coefficient test was used to correlate ICARS with NPCRS, midsagittal vermis relative diameter and IQ.

RESULTS

ICARS and ICARS subscores differed between patients and controls (p < 0.001). Interobserver agreement of ICARS was "almost perfect" (ICC = 0.99), with a "good" internal reliability (Cronbach's alpha = 0.72). ICARS was significantly correlated with the total NPCRS score (rs 0.90, p < 0.001). However, there was no agreement regarding categories of severity. Regarding neuroimaging, inverse correlations between ICARS and midsagittal vermis relative diameter (rs -0.85, p = 0.003) and IQ (rs -0.94, p = 0.005) were found. Patients bearing p.E93A, p.C241S or p.R162W mutations presented a milder phenotype.

CONCLUSIONS

ICARS is a reliable instrument for assessment of PMM2-CDG patients, without significant inter-rater variability. Despite our limited sample size, the results show a good correlation between functional cerebellar assessment, IQ and neuroimaging. For the first a correlation between ICARS, neuroimaging and IQ in PMM2-CDG patients has been demonstrated.

Sensitivity of spatiotemporal gait parameters in measuring disease severity in Friedreich ataxia

Friedreich ataxia (FRDA) is an autosomal recessive disease with gait ataxia being the main source of morbidity. Mobility progressively declines, from initial symptom onset at approximately 10-15 years of age to being unable to ambulate 10-15 years later. Here, we sought to investigate the relationship between spatiotemporal gait parameters and clinical markers of disease severity. Thirteen people with FRDA walked along an 8.3-m GAITRite® mat six times each at their preferred fast and slow speeds. Relationships between spatiotemporal gait parameters and a range of clinical and disease characteristics were examined. Significant correlations were found between spatiotemporal gait characteristics at each of the walking speeds and Friedreich Ataxia Rating Scale (FARS) score and disease duration. During the fast-walking condition, gait speed and cadence decreased with an increase in disease duration and the FARS score. GAA1 repeat expansion negatively correlated with double-support percentage of the gait cycle in all speed conditions demonstrating a relationship between the genetic mutation and compensatory strategies for impaired dynamic balance. In all speed conditions, there were correlations between a range of spatiotemporal gait characteristics and the timed 25-ft walk test, a well-established measure of gait mobility. These findings suggest that spatiotemporal gait parameters are a sensitive measure of gait decline in individuals with FRDA and should be considered for inclusion in intervention studies whilst participants are still ambulant.

Ataxia rating scales are age-dependent in healthy children

AIM

To investigate ataxia rating scales in children for reliability and the effect of age and sex.

METHOD

Three independent neuropaediatric observers cross-sectionally scored a set of paediatric ataxia rating scales in a group of 52 healthy children (26 males, 26 females) aged 4 to 16 years (mean age 10y 5mo SD 3y 11mo). The investigated scales involved the commonly applied International Cooperative Ataxia Rating Scale (ICARS), the Scale for Assessment and Rating of Ataxia (SARA), the Brief Ataxia Rating Scale (BARS), and PEG-board tests. We investigated the interrelatedness between individual ataxia scales, the influence of age and sex, inter- and intra-observer agreement, and test-retest reliability.

RESULTS

Spearman's rank correlations revealed strong correlations between ICARS, SARA BARS, and PEG-board test (all p<0.001). ICARS, SARA, BARS and PEG-board test outcomes were age-dependent until 12.5, 10, 11, and 11.5 years of age respectively. Intraclass correlation coefficients (ICCs) varied between moderate and almost perfect (interobserver agreement: 0.85, 0.72, and 0.69; intraobserver agreement: 0.92, 0.94, and 0.70; and test-retest reliability: 0.95, 0.50, and 0.71; for ICARS, SARA, and BARS respectively). Interobserver variability decreased after the sixth year of life.

INTERPRETATION

In healthy children, ataxia rating scales are reliable, but should include age-dependent interpretation in children up to 12 years of age. To enable longitudinal interpretation of quantitative ataxia rating scales in children, European paediatric normative values are necessary.

Prevalence of ataxia in children: a systematic review

OBJECTIVE

To estimate the prevalence of childhood ataxia resulting from both genetic and acquired causes.

METHODS

A systematic review was conducted following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) statement. Five databases were searched for articles reporting a frequency measure (e.g., prevalence, incidence) of ataxia in children. Included articles were first grouped according to the World Health Organization (WHO) regions and subsequently classified according to etiology (genetic, acquired, or mixed). Each article was assessed for its risk of bias on the domains of sampling, measurement, and analysis. Incidence values were converted to prevalence estimates whenever possible. European prevalence estimates for different etiologies of ataxia were summed to gauge the overall prevalence of childhood ataxia.

RESULTS

One hundred fifteen articles were included in the review. More than 50% of the data originated from the Europe WHO region. Data from this region also showed the least susceptibility to bias. Little data were available for Africa and Southeast Asia. The prevalence of acquired ataxias was found to vary more greatly across regions than the genetic ataxias. Ataxic cerebral palsy was found to be a significant contributor to the overall prevalence of childhood ataxia across WHO regions. The prevalence of childhood ataxias in Europe was estimated to be ∼26/100,000 children and likely reflects a minimum prevalence worldwide.

CONCLUSIONS

The findings show that ataxia is a common childhood motor disorder with a higher prevalence than previously assumed. More research concerning the epidemiology, assessment, and treatment of childhood ataxia is warranted.

Bioenergetics of the calf muscle in Friedreich ataxia patients measured by 31P-MRS before and after treatment with recombinant human erythropoietin

Friedreich ataxia (FRDA) is caused by a GAA repeat expansion in the FXN gene leading to reduced expression of the mitochondrial protein frataxin. Recombinant human erythropoietin (rhuEPO) is suggested to increase frataxin levels, alter mitochondrial function and improve clinical scores in FRDA patients. Aim of the present pilot study was to investigate mitochondrial metabolism of skeletal muscle tissue in FRDA patients and examine effects of rhuEPO administration by phosphorus 31 magnetic resonance spectroscopy (31P MRS). Seven genetically confirmed FRDA patients underwent 31P MRS of the calf muscles using a rest-exercise-recovery protocol before and after receiving 3000 IU of rhuEPO for eight weeks. FRDA patients showed more rapid phosphocreatine (PCr) depletion and increased accumulation of inorganic phosphate (Pi) during incremental exercise as compared to controls. After maximal exhaustive exercise prolonged regeneration of PCR and slowed decline in Pi can be seen in FRDA. PCr regeneration as hallmark of mitochondrial ATP production revealed correlation to activity of complex II/III of the respiratory chain and to demographic values. PCr and Pi kinetics were not influenced by rhuEPO administration. Our results confirm mitochondrial dysfunction and exercise intolerance due to impaired oxidative phosphorylation in skeletal muscle tissue of FRDA patients. MRS did not show improved mitochondrial bioenergetics after eight weeks of rhuEPO exposition in skeletal muscle tissue of FRDA patients.

Trial Registration

EU Clinical Trials Register2008-000040-13