Brain lesions in Friedreich's ataxia

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.

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.

Reactive Bergmann glia play a central role in spinocerebellar ataxia inflammation via the JNK pathway

The spinocerebellar ataxias (SCAs) are devastating neurological diseases characterized by progressive cerebellar incoordination. While neurons bear the brunt of the pathology, a growing body of evidence suggests that glial cells are also affected. It has, however, been difficult to understand the role of glia, given the diversity of subtypes, each with their individual contributions to neuronal health. Using human SCA autopsy samples we have discovered that Bergmann glia-the radial glia of the cerebellum, which form intimate functional connections with cerebellar Purkinje neurons-display inflammatory JNK-dependent c-Jun phosphorylation. This phosphorylation defines a signaling pathway not observed in other activated glial populations, providing an opportunity to isolate the role of Bergmann glia in SCA inflammation. Turning to an SCA1 mouse model as a paradigmatic SCA, we demonstrate that inhibiting the JNK pathway reduces Bergmann glia inflammation accompanied by improvements in the SCA1 phenotype both behaviorally and pathologically. These findings demonstrate the causal role for Bergmann glia inflammation in SCA1 and point to a novel therapeutic strategy that could span several ataxic syndromes where Bergmann glia inflammation is a major feature.

Progressive Spinal Cord Degeneration in Friedreich's Ataxia: Results from ENIGMA-Ataxia

BACKGROUND

Spinal cord damage is a hallmark of Friedreich's ataxia (FRDA), but its progression and clinical correlates remain unclear.

OBJECTIVE

The objective of this study was to perform a characterization of cervical spinal cord structural damage in a large multisite FRDA cohort.

METHODS

We performed a cross-sectional analysis of cervical spinal cord (C1-C4) cross-sectional area (CSA) and eccentricity using magnetic resonance imaging data from eight sites within the ENIGMA-Ataxia initiative, including 256 individuals with FRDA and 223 age- and sex-matched control subjects. Correlations and subgroup analyses within the FRDA cohort were undertaken based on disease duration, ataxia severity, and onset age.

RESULTS

Individuals with FRDA, relative to control subjects, had significantly reduced CSA at all examined levels, with large effect sizes (d > 2.1) and significant correlations with disease severity (r < -0.4). Similarly, we found significantly increased eccentricity (d > 1.2), but without significant clinical correlations. Subgroup analyses showed that CSA and eccentricity are abnormal at all disease stages. However, although CSA appears to decrease progressively, eccentricity remains stable over time.

CONCLUSIONS

Previous research has shown that increased eccentricity reflects dorsal column (DC) damage, while decreased CSA reflects either DC or corticospinal tract (CST) damage, or both. Hence our data support the hypothesis that damage to the DC and damage to CST follow distinct courses in FRDA: developmental abnormalities likely define the DC, while CST alterations may be both developmental and degenerative. These results provide new insights about FRDA pathogenesis and indicate that CSA of the cervical spinal cord should be investigated further as a potential biomarker of disease progression. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Tract-Specific Spinal Cord Diffusion Tensor Imaging in Friedreich's Ataxia

BACKGROUND

Spinal cord (SC) damage is a hallmark in Friedreich's ataxia (FRDA). Neuroimaging has been able to capture some SC macroscopic changes, but no study has evaluated microstructural SC white matter (WM) damage in vivo.

OBJECTIVES

We designed a cross-sectional study to evaluate microstructural integrity in SC WM tracts of FRDA patients using diffusion tensor imaging (DTI) with an automated analysis pipeline.

METHODS

Thirty patients and 30 matched healthy controls underwent 3 Tesla (T) magnetic resonance imaging (MRI). We obtained cervical SC T2 and diffusion-weighted imaging (DWI) acquisitions. Images were processed using the Spinal Cord Toolbox v.4.3.0. For levels C2-C5, we measured cross-sectional area (CSA) and WM DTI parameters (axial diffusivity [AD], fractional anisotropy [FA], radial diffusivity [RD], and mean diffusivity [MD]). Age, duration, and FARS scores were also obtained.

RESULTS

Mean age and disease duration of patients were 31 ± 10 and 11 ± 9 years, respectively. There was CSA reduction in FRDA amongst all levels. Between-group differences in FA, MD, and RD in total white matter (TWM), dorsal columns (DC), fasciculus gracilis (FG), fasciculus cuneatus (FC), and corticospinal tracts (CST) were present in all levels. FA and RD from TWM, DC, FC, and CST correlated with FARS scores, and in CST they also correlated with disease duration.

CONCLUSION

DTI uncovered abnormalities in SC WM tracts, which correlated with clinical features in FRDA. CSA and CST FA in C2 correlated best with disease severity, whereas DC FA showed the largest effect size to differentiate patients and healthy controls. SC WM microstructure is a potential neuroimaging biomarker to be explored in the disease. © 2021 International Parkinson and Movement Disorder Society.

The Pathology of the Vestibular System in CANVAS

OBJECTIVE

To describe the site of lesion responsible for the severe, bilateral, symmetrical, selective loss of vestibular function in Cerebellar Ataxia with Neuronopathy and Vestibular Areflexia Syndrome (CANVAS), an adult-onset recessively-inherited ataxia, characterized by progressive imbalance due to a combination of cerebellar, somatosensory, and selective vestibular impairment with normal hearing.

METHODS

Histologic examination of five temporal bones and the brainstems from four CANVAS patients and the brainstem only from one more, each diagnosed and followed from diagnosis to death by one of the clinician authors.

RESULTS

All five temporal bones showed severe loss of vestibular ganglion cells (cell counts 3-16% of normal), and atrophy of the vestibular nerves, whereas vestibular receptor hair cells and the vestibular nuclei were preserved. In contrast, auditory receptor hair cells, the auditory ganglia (cell counts 51-100% of normal), and the auditory nerves were relatively preserved. In addition, the cranial sensory ganglia (geniculate and trigeminal), present in two temporal bones, also showed severe degeneration.

CONCLUSIONS

In CANVAS there is a severe cranial sensory ganglionopathy neuronopathy (ganglionopathy) involving the vestibular, facial, and trigeminal ganglia but sparing the auditory ganglia. These observations, when coupled with the known spinal dorsal root ganglionopathy in CANVAS, indicate a shared pathogenesis of its somatosensory and cranial nerve manifestations. This is the first published account of both the otopathology and neuropathology of CANVAS, a disease that involves the central as well as the peripheral nervous system.

Vestibular impact of Friedreich ataxia in early onset patients

Background

Friedreich ataxia (FRDA) is the most frequent form of inherited ataxias. Vestibular and auditory assessments are not commonly part of the check up for these patients despite hearing and balance complaints. Screening of vestibular and auditory function was performed in a large group of young patients with genetically confirmed FRDA.

Methods

Our study included 43 patients (7–24 years of age). A complete vestibular assessment was performed including the canals function evaluation at 3 head velocities (bithermal caloric test, earth vertical axis rotation (EVAR) and head impulse test (HIT)) and otolith function evaluation (cervical vestibular evoked myogenic potentials). Information regarding the hearing evaluation of the patients were also retrieved including impedance tympanometry, distortion product otoacoustic emissions (DPOAEs), air and bone conduction audiometry and auditory brainstem response (ABR).

Results

Vestibular responses were impaired for canal responses (only at high and middle head velocities) and vestibulospinal otolithic responses. Abnormal neural conduction in the central auditory pathways was frequently observed. Oculomotor abnormalities were frequent, mostly hypermetric saccades and gaze instability. Inhibition of the vestibulo-ocular reflex by fixation was normal.

Conclusions

We show that Friedreich ataxia, even at onset, frequently associate saccadic intrusions, abnormal ABRs and decreased vestibulo-ocular and vestibulospinal responses progressing over time. These sensory impairments combined with ataxia further impair patient’s autonomy. These vestibular, auditory and visual impairments could be used as markers of the severity and progression of the disease. Adding vestibular and auditory testing to Friedreich patient’s evaluation may help physicians improve patient’s management.

How to spot ocular abnormalities in progressive supranuclear palsy? A practical review

Background

For parkinsonian disorders, progressive supranuclear palsy (PSP) continues to be significant for differential diagnosis. PSP presents a range of ocular abnormalities that have been suggested as optional tools for its early detection, apart from the principal characteristic of postural unsteadiness. Nonetheless, such symptoms may be difficult to identify, particularly during the early onset stage of the disorder. It may also be problematic to recognize these symptoms for general practitioners who lack the required experience or physicians who are not specifically educated and proficient in ophthalmology or neurology.

Main body

Thus, here, a methodical evaluation was carried out to identify seven oculomotor abnormalities occurring in PSP, comprising square wave jerks, the speed and range of saccades (slow saccades and vertical supranuclear gaze palsy), ‘round the houses’ sign, decreased blink rate, blepharospasm, and apraxia of eyelid opening. Inspections were conducted using direct visual observation. An approach to distinguish these signs during a bedside examination was also established. When presenting in a patient with parkinsonism or dementia, the existence of such ocular abnormalities could increase the risk of PSP. For the distinction between PSP and other parkinsonian disorders, these signs hold significant value for physicians.

Conclusion

The authors urge all concerned physicians to check for such abnormalities with the naked eye in patients with parkinsonism. This method has advantages, including ease of application, reduced time-consumption, and requirement of minimal resources. It will also help physicians to conduct efficient diagnoses since many patients with PSP could intially present with ocular symptoms in busy outpatient clinics.

Electronic supplementary material

The online version of this article (10.1186/s40035-019-0160-1) contains supplementary material, which is available to authorized users.

Nasality in Friedreich ataxia

Perceptual speech research in Friedreich ataxia (FRDA) has identified altered nasality as a key component of the dysarthria profile, however the incidence and severity of abnormal nasality remains unknown. Utilizing objective and perceptual methods, data on the relationship between resonance, disease duration, severity, age of onset and genetic profiles were collated. Thirty-seven participants with FRDA and 24 healthy controls provided contemporaneous speech samples for perceptual analysis, and single word samples for acoustic analysis. A subset of participants (eight participants with FRDA and eight controls) underwent nasometry assessment. Twenty-seven participants with FRDA presented with hypernasality and five with hyponasality on perceptual assessment. Acoustic analysis revealed participants with FRDA had greater nasality than controls (p < 0.05). Perceptual ratings of hypernasality correlated with GAA2 repeat length (ρ = 0.37, p = 0.03). Findings highlight the variability of nasality in FRDA, potentially reflecting variation in the neuropathological profile. Data also suggest the influence of genetic profiles on nasality.

Optical coherence tomography and visual field findings in patients with Friedreich ataxia

BACKGROUND

To investigate the optical coherence tomography (OCT) and visual field findings in Friedreich ataxia (FRDA).

METHODS

Ten eyes of 10 patients with genetically confirmed FRDA were included in this study. Twenty-two eyes of 22 age- and sex-matched volunteers served as controls. All eyes were examined with spectral domain OCT (Retinascan Advanced RS-3000; NIDEK) and Humphrey Field Analyzer (HFA II 750; Zeiss-Humphrey Systems).

RESULTS

OCT measurements of the average peripapillary retinal nerve fiber layer (RNFL) thickness, average peripapillary retinal thickness (RT), and foveal RT showed a statistically significant reduction in patients with FRDA (P < 0.0001). There was no statistically significant difference in choroidal thickness. OCT measurements of horizontal cup-to-disc (C/D) ratio, vertical C/D ratio, and average cup area were significantly increased in patients with FRDA. Visual acuity was significantly correlated with age at onset (P = 0.021) and average RNFL value (P = 0.045). There was a significant correlation between foveal thickness and disease duration (P = 0.014). Mean RNFL thickness was significantly correlated with the severity of neurological involvement (P = 0.039). Visual field testing (VFT) revealed a generalized reduction of sensitivity in the patients.

CONCLUSION

Patients with FRDA may have a measurable degree of retinal thinning as determined by OCT and a generalized reduction of sensitivity in VFT. Combining structural and functional findings may be used in the follow-up of patients with FRDA.

Nikolaus Friedreich and degenerative atrophy of the dorsal columns of the spinal cord

Nikolaus Friedreich (1825-1882) presented clinical findings in six patients with a severe hereditary disorder of the nervous system and secured full autopsies in four of them. He was fascinated by the spinal cord lesions in the siblings of two unrelated families, and in the first three of his five long articles stressed the destruction of the dorsal columns. He recognized the relatively minor symmetrical lesions of the anterolateral fasciculi but did not separate dorsal spinocerebellar tracts (Flechsig's bundles) and corticospinal tracts. Although he studied the dorsal spinal roots in great detail and established their principal abnormality, namely, axonal thinning without axonal loss, he reported dorsal root ganglia as entirely normal. He made an insightful description of atrophic neurons in the gracile nuclei (clavae) but overlooked the invariable atrophy of the dentate nuclei. He followed the families over a period of 14 years, but acknowledged the hereditary nature of the disease only very late. He proposed a developmental defect for the medulla oblongata, retaining his interpretation that the spinal lesion was inflammatory. This review honors Friedreich for his insight into a 'new' disease in the late 19th century and updates his neuropathological findings. It is remarkable that Friedreich also described the abnormal hearts in the disease that now bears his name since hypertrophic cardiomyopathy is now recognized as the main cause of death in Friedreich's ataxia.

Cognition in Friedreich ataxia

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

Friedreich ataxia: neuropathology revised

Friedreich ataxia is an autosomal recessive disorder that affects children and young adults. The mutation consists of a homozygous guanine-adenine-adenine trinucleotide repeat expansion that causes deficiency of frataxin, a small nuclear genome-encoded mitochondrial protein. Low frataxin levels lead to insufficient biosynthesis of iron-sulfur clusters that are required for mitochondrial electron transport and assembly of functional aconitase, and iron dysmetabolism of the entire cell. This review of the neuropathology of Friedreich ataxia stresses the critical role of hypoplasia and superimposed atrophy of dorsal root ganglia. Progressive destruction of dorsal root ganglia accounts for thinning of dorsal roots, degeneration of dorsal columns, transsynaptic atrophy of nerve cells in Clarke column and dorsal spinocerebellar fibers, atrophy of gracile and cuneate nuclei, and neuropathy of sensory nerves. The lesion of the dentate nucleus consists of progressive and selective atrophy of large glutamatergic neurons and grumose degeneration of corticonuclear synaptic terminals that contain γ-aminobutyric acid (GABA). Small GABA-ergic neurons and their projection fibers in the dentato-olivary tract survive. Atrophy of Betz cells and corticospinal tracts constitute a second intrinsic CNS lesion. In light of the selective vulnerability of organs and tissues to systemic frataxin deficiency, many questions about the pathogenesis of Friedreich ataxia remain.

The cerebellar component of Friedreich's ataxia

Lack of frataxin in Friedreich's ataxia (FRDA) causes a complex neurological and pathological phenotype. Progressive atrophy of the dentate nucleus (DN) is a major intrinsic central nervous system lesion. Antibodies to neuron-specific enolase (NSE), calbindin, glutamic acid decarboxylase (GAD), and vesicular glutamate transporters 1 and 2 (VGluT1, VGluT2) allowed insight into the disturbed synaptic circuitry of the DN. The available case material included autopsy specimens of 24 patients with genetically defined FRDA and 14 normal controls. In FRDA, the cerebellar cortex revealed intact Purkinje cell somata and dendrites as assessed by calbindin immunoreactivity. The DN, however, displayed severe loss of large NSE-reactive neurons. Small neurons remained intact. Labeling of Purkinje cells, basket fibers, Golgi neurons, and Golgi axonal plexuses with antibodies to GAD indicated normal intrinsic circuitry of the cerebellar cortex involving γ-aminobutyric acid (GABA). In contrast, the DN displayed severe loss of GABA-ergic terminals and formation of GAD- and calbindin-reactive grumose degeneration. The surviving small GAD-positive DN neurons provided normal GABA-ergic terminals to intact inferior olivary nuclei. The olives also received normal glutamatergic terminals as shown by VGluT2-reactivity. VGluT1-immunocytochemistry of the cerebellar cortex confirmed normal glutamatergic input to the molecular layer by parallel fibers and the granular layer by mossy fibers. VGluT2-immunoreactivity visualized normal climbing fibers and mossy fiber terminals. The DN, however, showed depletion of VGluT1- and VGluT2-reactive terminals arising from climbing and mossy fiber collaterals. The main functional deficit underlying cerebellar ataxia in FRDA is defective processing of inhibitory and excitatory impulses that converge on the large neurons of the DN. The reason for the selective vulnerability of these nerve cells remains elusive.

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.

(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.

Disruption to higher order processes in Friedreich ataxia

Friedreich ataxia (FRDA), the most common of the genetically inherited ataxias, is characterised by ocular motor deficits largely reflecting disruption to brainstem-cerebellar circuitry. These deficits include fixation instability, saccadic dysmetria, disrupted pursuit, and vestibular abnormalities. Whether higher order or cognitive control processes involved the generation of more volitional eye movements are similarly impaired, has not been explored previously. This research examined antisaccade and memory-guided saccade characteristics in 13 individuals with genetically confirmed FRDA, and contrasted performance with neurologically healthy individuals. We demonstrate, for the first time, a broad range of deficits in FDRA consistent with disruption to higher order processes involved in the control of saccadic eye movement. Significant differences between FDRA and control participants were revealed across all movement parameters (latency, gain, velocity, position error), and across all saccade types, including alterations to velocity profiles. FDRA participants also generated significantly more erroneous responses to non-target stimuli in both saccade paradigms. Finally, a number of correlations between ocular motor and clinical measures were revealed including those between contrast acuity and saccadic latency (all saccade types), disease duration and measures of response inhibition (errors and relative latencies for antisaccades), and neurological scores and error latencies, arguably a reflection of difficulty resolving response conflict. These results suggest a role for the cerebellum in higher order cognitive control processes, and further support the proposal that eye movement markers, which can be measured with accuracy and reliability, may be a useful biomarker in FDRA.

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

Friedreich's ataxia (FA) is the most frequent autosomal recessive ataxia and essentially considered a disease of the dorsal root ganglia and spinal cord. It is caused by homozygous GAA expansions in the Frataxin gene in most cases. Although only a few studies have addressed cerebral involvement in FA, cognitive symptoms have lately been emphasized. To evaluate brain damage in vivo, we employed whole-brain VBM and analysis of pre-defined regions of interest (ROIs) over the cerebellum to compare 24 patients with 24 age-and-sex-matched normal controls. (1)H-MRS of deep cerebral white matter (WM) was subsequently performed. Mean age of patients was 28 years (range 14-45), mean duration of disease was 14 years (range 5-28) and 11 were men. Mean length of shorter (GAA1) and longer (GAA2) alleles were 735 and 863, respectively. VBM analysis identified WM atrophy in the posterior cyngulate gyrus, paracentral lobule and middle frontal gyrus. ROIs over the infero-medial cerebellar hemispheres and dorsal brainstem presented gray matter atrophy, which correlated with duration of disease (r = -0.4). NAA/Cr ratios were smaller among patients (P = 0.006), but not Cho/Cr (P = 0.08). Our results provide evidence of axonal damage in the cerebellum, brainstem and subcortical WM in FA. This suggests that neuronal dysfunction is more widespread than previously thought in FA.

Differential impairment in semantic, phonemic, and action fluency performance in Friedreich's ataxia: possible evidence of prefrontal dysfunction

This study examined phonemic (letters), semantic (animals) and action verbal fluency cues in twenty-four patients with FRDA, and twenty matched healthy control subjects. The Action Fluency Test (AFT) is a newly-developed verbal fluency cue that consists in asking the subject to rapidly generate verbs. Given the high presence of dysarthria and cognitive slowness in FRDA patients, control tasks were administered in order to dissociate motor/articulatory impairment and cognitive slowness from verbal fluency deficit. Results showed that patients and control subjects performed similarly on the semantic fluency task. In contrast, patients performed significantly poorer on phonemic and action fluency tests. Correlational analyses showed that the deficits cannot be attributed to dysarthria or cognitive slowness. Although executive processes are necessary for initiating and monitoring all verbal fluency tasks, phonemic and action fluency may place a greater burden on strategic processes, given that they require a more unusual type of lexicon search. Thus, the deficits found occur in tasks that require greater executive/prefrontal control. This impairment might be the result of an affectation of cerebellum-prefrontal cortex connections, although the possibility of a primary prefrontal dysfunction remains to be investigated.

The dentate nucleus in Friedreich's ataxia: the role of iron-responsive proteins

Frataxin deficiency in Friedreich's ataxia (FRDA) causes cardiac, endocrine, and nervous system manifestations. Frataxin is a mitochondrial protein, and adequate amounts are essential for cellular iron homeostasis. The main histological lesion in the brain of FRDA patients is neuronal atrophy and a peculiar proliferation of synaptic terminals in the dentate nucleus termed grumose degeneration. This cerebellar nucleus may be especially susceptible to FRDA because it contains abundant iron. We examined total iron and selected iron-responsive proteins in the dentate nucleus of nine patients with FRDA and nine normal controls by biochemical and microscopic techniques. Total iron (1.53 +/- 0.53 mumol/g wet weight) and ferritin (206.9 +/- 46.6 mug/g wet weight) in FRDA did not significantly differ from normal controls (iron: 1.78 +/- 0.88 mumol/g; ferritin: 210.9 +/- 9.0 mug/g) but Western blots exhibited a shift to light ferritin subunits. Immunocytochemistry of the dentate nucleus revealed loss of juxtaneuronal ferritin-containing oligodendroglia and prominent ferritin immunoreactivity in microglia and astrocytes. Mitochondrial ferritin was not detectable by immunocytochemistry. Stains for the divalent metal transporter 1 confirmed neuronal loss while endothelial cells reacting with antibodies to transferrin receptor 1 protein showed crowding of blood vessels due to collapse of the normal neuropil. Regions of grumose degeneration were strongly reactive for ferroportin. Purkinje cell bodies, their dendrites and axons, were also ferroportin-positive, and it is likely that grumose degeneration is the morphological manifestation of mitochondrial iron dysmetabolism in the terminals of corticonuclear fibers. Neuronal loss in the dentate nucleus is the likely result of trans-synaptic degeneration.

Dysarthria and Friedreich's ataxia: what can intelligibility assessment tell us?

BACKGROUND

Friedreich's ataxia is one of the most common hereditary disorders of the nervous system. Dysarthria is a pervasive symptom of Friedreich's ataxia, yet the clinical presentation of speech symptoms remains poorly understood, leaving clinicians without the evidence required to develop therapy interventions.

AIMS

The research reported herein had three aims: the first was to document the severity of the intelligibility deficit associated with Friedreich's ataxia dysarthria; the second was to document the phonetic profile of the intelligibility deficit; and the third was to use the results of the phonetic profile to estimate the motor control mechanisms and neurological substrates implicated in Friedreich's ataxia dysarthria.

METHODS & PROCEDURES

Eleven adult males with Friedreich's ataxia were recruited. Intelligibility was assessed using a single-word multiple-choice task completed by ten listeners.

OUTCOMES & RESULTS

Intelligibility severity ratings ranged from mild to severe. The majority of subjects fell into the mild category. The phonetic errors revealed a distinctive profile, with word-final plosive voicing contrast representing the highest source of error. Involvement of cerebro-cerebellar loops was considered to be compatible with the profile results.

CONCLUSIONS

Friedreich's ataxia dysarthria has a distinctive phonetic profile and contains subgroups of different severity. High sources of error identified in the phonetic profile should be considered when developing targets for therapy intervention. Neurological substrates are considered to vary across individuals and to include involvement of cerebro-cerebellar loops. Further research involving acoustic analysis of final plosive voicing contrasts would provide further insights into the neurological substrates involved.

A child with Friedreich's ataxia and epilepsy

Epilepsy in Friedreich's ataxia is rare. We describe a 9-year-old boy with Friedreich's ataxia who had onset of symptoms in the second year of life and developed a generalized epilepsy at age 5 years. On cerebral magnetic resonance imaging, he has a subependymal gray-matter heterotopia. We suggest that his gray-matter heterotopia might be related to his diagnosis of Friedreich's ataxia and that his early onset of symptoms might be related to the length of his guanine-adenine-adenine (GAA) triplet repeat expansion.

Vestibulo-ocular arreflexia in families with spinocerebellar ataxia type 3 (Machado-Joseph disease)

OBJECTIVE

To identify the presence of vestibulo-ocular arreflexia in patients with Machado-Joseph disease (MJD), which can easily be diagnosed at the bedside.

METHODS

Seven patients with MJD from five unrelated families and 11 patients with sporadic or hereditary cerebellar ataxia other than MJD underwent a detailed neuro-otological and oculomotor examination. Six MJD and five non-MJD patients also underwent electro-oculographic recordings and caloric tests.

RESULTS

Gaze evoked nystagmus, smooth pursuit, and saccade abnormalities were found in both MJD and non-MJD patients. However, in all seven MJD patients but in none of the non-MJD patients, sudden passively induced head thrust to both sides elicited pathological corrective catch-up saccades, indicating bilateral loss of the horizontal vestibulo-ocular reflex. This was further confirmed in six MJD patients who had absent vestibular response to both a standard caloric test and ice water ear irrigation. Nystagmus was induced by standard caloric irrigation in all non-MJD patients examined. There was no correlation between the loss of vestibular function and the severity of cerebellar impairment.

CONCLUSIONS

The presence of vestibulo-ocular arreflexia, as measured by the head thrust test in a patient with dominant cerebellar ataxia, strongly suggests the diagnosis of MJD.

Genetic ataxia

Advances in molecular genetics have led to identification of an increasing number of genes responsible for inherited ataxic disorders. Consequently, DNA testing has become a powerful method to unambiguously establish the diagnosis in some of these disorders; however, there are limitations in this approach. Furthermore, the ethical, social, legal and psychological implications of the genetic test results are complex, necessitating appropriate counseling. This article intends to help the practicing neurologist clinically differentiate these disorders, choose appropriate genetic tests, and recognize the importance of counseling.

Influence of GAA expansion size and disease duration on central nervous system impairment in Friedreich's ataxia: contribution to the understanding of the pathophysiology of the disease

OBJECTIVE

To verify if GAA expansion size could account for the severity of the central nervous system involvement in Friedreich's ataxia (FA).

METHODS

Retrospective study of 52 FA patients (mean age 26.9+/-12.1 years; mean disease duration 10.6+/-7.6 years) homozygous for GAA expansion. Median nerve somatosensory evoked potentials (SSEPs) were available in 36 FA patients, upper limb motor evoked potentials (MEPs) to transcranial magnetic stimulation in 32, brainstem auditory evoked potentials (BAEPs) in 24, and visual evoked potentials (VEPs) in 34. N20, P100, MEP amplitude, SSEP and MEP central conduction time (CCT and CMCT), P100 latency and I-III and I-V interpeak latency, and a BAEP abnormality score were correlated with disease duration and GAA expansion size on the shorter (GAA1) and larger (GAA2) allele in each pair.

RESULTS

The GAA1 size inversely correlated with the N20 amplitude (r = -0.49; P<0. 01). Disease duration directly correlated with CMCT (r = 0.57; P<0.01) and BAEP score (r = 0.61; P<0.01) and inversely with MEP (r = -0.40; P<0.05) and P100 amplitude (r = -0.39; P<0.05).

CONCLUSIONS

Our data suggest that central somatosensory pathway involvement in FA is mainly determined by GAA1 expansion size. Vice versa, degeneration of pyramidal tracts, auditory and visual pathways seems to be a continuing process during the life of FA patients.

Absence of a common functional denominator of visual disturbances in cerebellar disease

Several studies have demonstrated disturbances of visual perception in patients suffering from cerebellar disease. In an attempt to determine the cause of these visual disturbances and thereby the cerebellar contribution to vision, we designed two sets of experiments in which we tested (i) the possibility of a general magnocellular deficit in cerebellar disease and (ii) the alternative possibility of impaired spatial attention underlying visual disturbances in cerebellar patients. The first set of experiments consisted of a test of position discrimination, a parvocellular function and tests tapping different aspects of motion perception including speed discrimination, direction discrimination and the ability to extract a coherent motion signal embedded in noise. The second set of experiments compared the performance on two different classes of texture discrimination. The first one required fast and precise shifts of focal spatial attention ('serial search'), the second one, testing preattentive texture discrimination ('pop-out'), did not. In the first set of experiments cerebellar patients were impaired on the position discrimination task as well as several, albeit not all, tests of motion perception. The pattern of disturbances obtained was neither compatible with the notion of a selective magnocellular deficit nor the idea, originally put forward by Ivry and Diener (J Cogn Neurosci 1991; 3: 355-66) that visual deficits are secondary to an impaired measurement of time. In the second set of experiments, cerebellar patients showed normal performance on pop-out tasks and normal performance on all variants of the serial search task except for the one requiring comparison of a single element presented with a sample of the target in short-term memory. In summary, our results support the existence of visual disturbances in cerebellar disease, but provide evidence against a common, simple denominator such as a timing deficit, deficient cerebellar modulation of magnocellular circuitry, deficits of spatial attention or visual working memory.

Infantile onset spinocerebellar ataxia with sensory neuropathy (IOSCA): neuropathological features

Infantile onset spinocerebellar ataxia (IOSCA, MIM 271245) is a recessively inherited, progressive neurological disease, which we have described in 19 Finnish patients. The clinical symptoms of IOSCA include ataxia, athetosis, hypotonia, hearing deficit, ophthalmoplegia, sensory neuropathy, female hypogonadism, and epilepsy as a late manifestation. We have mapped the IOSCA locus to 10q24. In our two autopsy cases of IOSCA, the neuropathological findings were almost uniform. The cerebral hemispheres were quite well preserved, but the brain stem and the cerebellum were moderately atrophic. The most severe atrophic changes were seen in the spinal cord: in the dorsal roots, the posterior columns and the posterior spinocerebellar tracts. There was a severe neuronal loss in the dorsal nucleus (Clarke's column) of both cases and slight atrophy of the intermediolateral column in one case. The cerebellar peduncles, the inferior olives, the accessory cuneate nuclei and especially the dentate nuclei were atrophic and gliotic. The eighth cranial nerve and nucleus were atrophic. The ventral pontine nuclei and transverse fibers were slightly affected. Tegmental nuclei and tracts, especially sensory structures, were more severely affected. In mesencephalon, there was atrophy of the oculomotor nuclear complex and periaqueductal gray matter. The cerebellar cortex showed patchy atrophy. Degenerative changes were seen in dorsal root ganglia, and there was a severe axonal loss in the sural nerve. The neuropathological picture of IOSCA thus seems close to that reported in Friedreich's ataxia, another recessively inherited usually childhood-onset ataxia.

Hereditary motor and sensory neuropathy associated with cerebellar atrophy (HMSNCA): clinical and neuropathological features of a Japanese family

We report clinicopathological features of a Japanese family with hereditary motor and sensory neuropathy associated with cerebellar atrophy (HMSNCA). Four affected members from a single generation were examined. They shared common clinical features, including insidious onset in teenage, slowly progressive cerebellar ataxia, amyotrophy, sensory disturbance, and dementia. In addition, all the patients showed hypoalbuminemia and hyperlipidemia and a marked atrophy of the cerebellum on magnetic resonance images. Autopsy of the proband revealed a severe loss of Purkinje cells, degeneration of posterior columns and spinocerebellar tracts of the spinal cord, and a marked loss of myelinated and unmyelinated fibers in the peripheral nerves. We consider that HMSNCA is a distinct form of hereditary multisystem neuronal degeneration.

Central motor conduction time by magnetic stimulation of the cortex and peripheral nerve conduction follow-up studies in Friedreich's ataxia

A follow-up clinical study, peripheral motor and sensory nerve conduction velocities and central motor conduction by magnetic stimulation of the cortex were performed in 13 patients with classical Friedreich's ataxia (FA) phenotype, for a period of 9-12 years. Clinical worsening was unrelated to peripheral nerve abnormalities. The amplitude of the nerve action potentials and delayed conduction velocity remained unchanged for several years. Central motor conduction times were abnormal in all patients. Clinical conditions worsened significantly between successive examinations with significant increments in threshold and significant decrement of the amplitude of motor evoked potentials. The results are consistent with progressive pyramidal and cerebellar pathways involvement as the cause of clinical worsening in FA.

Ophthalmologic findings in patients with ataxia

PURPOSE

To determine the frequency and spectrum of ophthalmologic findings in a large, heterogeneous group of patients with ataxia.

METHODS

Medical records of 184 patients from a university-based ataxia clinic were retrospectively reviewed. Patients were classified as having Friedreich's ataxia, spinocerebellar degeneration, cerebellar degeneration, familial or sporadic olivo-pontocerebellar atrophy, multisystem atrophy, spastic ataxia, myoclonic ataxia, or other diagnoses such as mitochondrial myopathy. All had complete ophthalmologic examinations, and 107 underwent electro-oculography.

RESULTS

Among 184 patients with ataxia, diplopia was present in 52 (28%), best-corrected visual acuity was decreased in 29 (16%), and oscillopsia was present in 10 (5%). Diplopia was usually caused by an intermittent, small-angle heterotropia. The reduction in best-corrected visual acuity varied from mild to profound and was caused by optic atrophy, retinal degeneration, or both. Optic atrophy was present most frequently in spastic ataxia (five of 22 patients) and myoclonic ataxia (two of eight patients), followed by Friedreich's ataxia (three of 26 patients). Retinal degeneration and ophthalmoplegia were most characteristically associated with familial olivopontocerebellar atrophy and mitochondrial myopathy. Laboratory testing of ocular motility showed frequent abnormalities in all groups. Fixation instability was most characteristic of Friedreich's ataxia, whereas saccadic slowing was noticeably absent from patients with purely cerebellar degenerations.

CONCLUSIONS

The ataxias may be associated with visual dysfunction caused by retinal degeneration, optic atrophy, oculomotor disturbance, or a combination of these.

Fixation instability and oculomotor abnormalities in Friedreich's ataxia

Eye movements were studied in 13 patients with Friedreich's ataxia and correlated with MRI findings to investigate whether oculomotor abnormalities can be traced to cerebellar disturbances in this disease. One of the most prominent eye signs was fixation instability (square-wave jerks, SWJ.). Besides SWJ the patients showed various combinations of cerebellar, vestibular and brain-stem oculomotor signs. Our patients did not comprise a homogeneous group with regard to their oculomotor findings. There was no correlation between the severity of any of the so-called cerebellar oculomotor disturbances and the number of SWJ. We tried to correlate the extent of oculomotor disturbances with floccular atrophy and atrophy of the dorsal vermis on MRI in seven of the patients. None of the oculomotor features (including SWJ) correlated with flocculus or dorsal vermis size. Furthermore, floccular and vermal measurements on MRI were normal. Accordingly, we think it unlikely that the oculomotor disturbances, including SWJ, are attributable to cerebellar pathology per se.

Event-related potentials in patients with cerebellar degeneration: electrophysiological evidence for cognitive impairment

We measured event-related potentials and reaction times during semantic discrimination tasks in 8 patients with cerebellar degeneration and in 10 normal subjects. The NA, N2 and P3 latencies of patients were significantly longer in patients, whereas N1 and P2 latencies did not differ between both groups. There was also no difference in the simple and GO/NOGO reaction times. These results suggest that these patients' impairment in cognitive information processing arose from a difficulty in pattern recognition of the stimuli represented by the NA component. These data also support the notion that the cerebellum plays a role in cognitive information processing.

Magnetic resonance imaging in "typical" and "late onset" Friedreich's disease and early onset cerebellar ataxia with retained tendon reflexes

MRI makes it possible to study the in vivo brain and spinal cord morphology of patients with hereditary ataxia. We performed T1- and T2-weighted studies in eleven patients with Friedreich's disease (FD), five with "late onset" FD and ten with early onset cerebellar ataxia with retained tendon reflexes (EOCA). Cervical cord atrophy was constant in FD and "late onset" FD and often associated with atrophy of the cerebellum and of the brainstem; T2-weighted studies showed posterior column degeneration in the cervical cord. The most frequent finding in EOCA was cerebellar atrophy, pure or associated with cervical cord or brainstem atrophy; the cerebellar atrophy was marked in a few cases and was related to disease duration.

Evoked potentials in inherited ataxias: a multimodal electrophysiological study

A multimodal electrophysiological study, including median nerve somatosensory evoked potentials (SSEPs), motor cortical stimulation (CS) and brainstem evoked potentials (BAEPs), was performed on 34 patients with hereditary ataxias (HAs): 15 with Friedreich's disease (FD), 10 with early onset cerebellar ataxia (EOCA), and 9 with autosomal dominant cerebellar ataxia (ADCA). A higher incidence of abnormal central motor conduction was observed in FD than in EOCA patients, but was never observed in ADCA. A relationship between central motor conduction abnormalities and disease duration and clinical impairment was found only in FD patients. All FD patients showed severe impairment of the SSEPs that was not related to disease duration. In EOCA patients, less frequent and more variable SSEP abnormalities were observed. The lowest incidence of central SSEP abnormalities was observed in ADCA. The BAEP findings in all 3 groups of patients (but particularly those with EOCA) suggest prevalent brainstem damage.

Magnetic resonance imaging in degenerative ataxic disorders

MRI of the brain was performed in 53 patients with a variety of degenerative ataxias and related disorders and 96 control subjects. Atrophy of intracranial structures was not seen in patients with the pure type of hereditary spastic paraplegia, or in early cases of Friedreich's ataxia. In advanced Friedreich's ataxia there was atrophy of the vermis and medulla. The MRI features of early onset cerebellar ataxia with retained reflexes were variable, and suggest heterogeneity. In autosomal dominant cerebellar ataxias, most patients had cerebellar and brainstem atrophy, probably reflecting the pathological process of olivopontocerebellar atrophy; there was no clearly defined group with both clinical and imaging features of isolated cerebellar involvement. The MRI abnormalities in idiopathic late onset cerebellar ataxia were predominantly those of cerebellar and brainstem atrophy or pure cerebellar atrophy. The clinical and imaging features of brainstem abnormalities were discordant in several patients. Pure cerebellar atrophy was associated with slower progression of disability. Cerebral atrophy was common in the late onset ataxias. Cerebral white matter lesions, although usually few in number, were observed in significantly more patients than controls, particularly those aged over 50 years.

Gene in the region of the Friedreich ataxia locus encodes a putative transmembrane protein expressed in the nervous system

Friedreich ataxia (FRDA) is an autosomal recessive degenerative disorder that affects the cerebellum, spinal cord, and peripheral nerves. The FRDA gene was localized in 9q13-q21 within 0.7 centimorgan of the D9S5 and D9S15 loci. One recently reported recombination event and haplotype analysis in a population with a founder effect suggested that the FRDA locus is on the D9S5 side. Using a conserved probe from the D9S5 locus, we have now identified an approximately 7-kilobase (kb) transcript and report cloning of its cDNA. The corresponding gene, X11, extends at least 80 kb in a direction opposite D9S15. The gene is expressed in the brain, including the cerebellum, but is not detectable in several nonneuronal tissues and cell lines. In situ hybridization of adult mouse brain sections showed prominant expression in the granular layer of the cerebellum. Expression was also found in the spinal cord. The cDNA contains an open reading frame encoding a 708-amino acid sequence that shows no significant similarity to other known proteins but contains a unique, 24-residue-long, putative transmembrane segment. On the basis of its genomic localization and its neuronal site of expression, particularly in the cerebellum, this "pioneer" gene represents a candidate for FRDA. Direct evidence of its involvement in FRDA will require a search for causative point mutations in patients.

Central motor conduction to upper and lower limbs after magnetic stimulation of the brain and peripheral nerve abnormalities in 20 patients with Friedreich's ataxia

Central motor conduction time (CMCT) to thenar and soleus muscles was measured after magnetic stimulation of the cortex in 20 cases of Friedreich's ataxia (FA) and was abnormal in all. CMCT values were related to disease duration and disability. The amplitude of CMAP after cortex stimulation was severely reduced in the most disabled patients. Reduction in amplitude of the nerve evoked potentials was related neither to disease duration nor grade of disability. These results suggest that clinical worsening in FA is mainly due to progressive central motor pathway involvement. CMCT study is a better index of disease progression than peripheral nerve examination. Abnormalities in CMCT may be the third electrophysiological diagnostic criterion in FA, after reduced amplitude of nerve action potentials and absent H reflex.

Brain-stem auditory evoked potentials and blink reflex in Friedreich's ataxia

The brain-stem involvement in Friedreich's ataxia (FA) was studied by using brain-stem auditory evoked potentials (BAEPs) and the blink reflex. Ten out of 18 patients had abnormal BAEPs, the main abnormality being complete absence of responses and disappearance of wave V. Combined degeneration of the peripheral and central acoustic pathways probably accounts for these findings. The blink reflex was abnormal in 50% of the cases. The outstanding abnormality was bilateral delay of late responses with normal early response, which could be correlated with the known pallor of the descending trigeminal tracts. In contrast with BAEP findings, blink reflex abnormalities did not correlate with either the age of patients or the severity and duration of the disease. These data suggest a difference in susceptibility to degeneration between the auditory system and neuronal system subserving the blink reflex. We conclude that systematic BAEP and blink reflex recording is useful in the electrophysiological evaluation of FA patients.

Cerebral glucose hypermetabolism in Friedreich's ataxia detected with positron emission tomography

Local cerebral metabolic rate for glucose was studied with 18F-2-fluoro-2-deoxy-D-glucose and positron emission tomography (PET) in 22 patients with Friedreich's ataxia and 23 age-matched normal control subjects. The diagnosis of Friedreich's ataxia was established by the history and physical findings and by excluding other diseases through laboratory investigations. PET studies revealed a statistically significant widespread increase of local cerebral metabolic rate for glucose in the brains of patients with Friedreich's ataxia who were still ambulatory, in comparison with normal control subjects. Nonambulatory patients with Friedreich's ataxia, in comparison with normal control subjects, had significantly increased local cerebral metabolic rates for glucose in the caudate and lenticular nuclei, but not in the other structures studied. The rate was significantly greater in ambulatory patients with Friedreich's ataxia than in nonambulatory patients in all structures studied except the caudate and lenticular nuclei. The data suggest that early in the course of Friedreich's ataxia, the local cerebral metabolic rate for glucose is increased extensively in the central nervous system, and as the disease progresses, it decreases in a regionally specific manner.

Positron emission tomography study of brain benzodiazepine receptors in Friedreich's ataxia

Central type benzodiazepine receptors were studied in 9 patients with Friedreich's ataxia and 12 healthy subjects using positron emission tomography (PET) and [11C]Ro 15-1788, a specific antagonist of the central type benzodiazepine receptors, as radioligand. A standard PET procedure was used in 5 patients and 8 controls to obtain brain kinetics of the total binding of the radioligand. The remaining subjects were intravenously injected with a saturating dose of unlabeled Ro 15-1788, 30 minutes after the tracer injection, to determine the nondisplaceable binding of [11C]Ro 15-1788. A semi-quantitative method was used to quantify the [11C]Ro 15-1788 data. None of the quantification indices in the cerebellar hemispheres, or in the other brain areas investigated, was significantly modified in patients with Friedreich's ataxia. These findings suggest that brain benzodiazepine receptors are unaffected in Friedreich's ataxia.

Significance of MRI-confirmed atrophy of the cranial spinal cord in Friedreich's ataxia

The severity of Friedreich's ataxia was graded in ten patients by clinical examination and in five by use of posturography. These data were compared with neuroradiology findings. CT-confirmed infratentorial atrophy occured only in advanced cases of Friedreich's ataxia; the correlation with the clinical score was poor. On mid-sagittal MRI planes the diameters of fourth ventricle, brain stem at the level of the inferior olive and spinal cord at the levels of the foramen magnum and C3 were measured. Patients with Friedreich's ataxia had significant MRI-confirmed atrophy of the cranial spinal cord as compared with a normal, age-matched control group. This was also observed in patients with Friedreich's ataxia in the early stages. A reliable correlation between atrophy of the cranial spinal cord and the clinical score, however, could again not be found. MRI exploration of the cranial spinal cord may be recommended as an additional diagnostic marker in Friedreich's ataxia.

Evoked potential studies in Friedreich's ataxia and progressive early onset cerebellar ataxia

We recorded somatosensory evoked potentials (SEP) in 15 patients affected by Friedreich's ataxia (FA) and in 9 patients with progressive early onset cerebellar ataxia (PEOCA). Brainstem auditory evoked potentials (BAEP) were also recorded in 14 FA patients and in five PEOCA patients. SEP results showed clear differences between groups of FA, evidence of peripheral involvement was seen in all patients, with absence of the N9 potential or a major reduction of its amplitude. In patients in whom central responses could be recorded, conduction velocity was normal or near normal up to the brainstem but was reduced from brainstem to cerebral cortex. Four patients with PEOCA had SEP abnormalities similar to those seen in FA. In the five other patients, the amplitude and latency of N9 were normal but conduction velocity was reduced from brainstem to cerebral cortex. In FA, BAEP were abnormal in all patients with a disease duration of four years or more but were normal in four of the five PEOCA patients. Systematic evoked potential recording is useful in the investigation of hereditary ataxias.

Central motor conduction in degenerative ataxic disorders: a magnetic stimulation study

Central motor conduction to small hand muscles was measured using magnetic stimulation of the motor cortex and electrical stimulation of proximal motor roots in 11 patients with Friedreich's ataxia, 10 patients with early onset cerebellar ataxia with retained tendon reflexes (EOCA) and 13 patients with late onset degenerative cerebellar disease (LOCD). Central motor conduction was abnormal in 91% with Friedreich's ataxia, 70% with EOCA and 38% with LOCD. Central motor conduction abnormalities were not specific to individual disorders but were more severe and were related to disease duration in Friedreich's ataxia and EOCA.

Monoclonal antibodies react with neuronal subpopulations in the human nervous system

Monoclonal antibody probes were used to identify antigenic cross reactivities among neuronal subpopulations and to dissect the human nervous system at several levels of organization. Six monoclonal antibodies, prepared with immunogens from Drosophila melanogaster or human nervous tissue, were used to localize antigens immunocytochemically in normal adult human neocortex, hippocampus, cerebellum, spinal cord, and retina. Four of the six antibodies were neural specific in their reactivity and each stained a unique combination of neurons. The antibodies reacted with at least three subpopulations of cerebral cortical neurons, including discrete populations of pyramidal and nonpyramidal cells. Components of a widely distributed functional system within the spinal cord and cerebellum were labelled by one antibody, which reacted with neurons in the nucleus dorsalis of Clarke, deep cerebellar nuclei, and Purkinje cells. At the single-cell level, three of the monoclonals differentially labelled the photoreceptor cell outer segment, inner segment, and perikaryon. Three of the six antibodies were reactive with specific protein bands on immunoblots of tissue homogenates. This monoclonal antibody panel provides a novel and potentially useful method of analysis of the organization of the normal and diseased human nervous system.