Nystagmus as an early ocular alteration in Machado-Joseph disease (MJD/SCA3)

Pre-ataxic loss of intrinsic plasticity and motor learning in a mouse model of SCA1

Spinocerebellar ataxias are neurodegenerative diseases, the hallmark symptom of which is the development of ataxia due to cerebellar dysfunction. Purkinje cells, the principal neurons of the cerebellar cortex, are the main cells affected in these disorders, but the sequence of pathological events leading to their dysfunction is poorly understood. Understanding the origins of Purkinje cells dysfunction before it manifests is imperative to interpret the functional and behavioural consequences of cerebellar-related disorders, providing an optimal timeline for therapeutic interventions. Here, we report the cascade of events leading to Purkinje cells dysfunction before the onset of ataxia in a mouse model of spinocerebellar ataxia 1 (SCA1). Spatiotemporal characterization of the ATXN1[82Q] SCA1 mouse model revealed high levels of the mutant ATXN1[82Q] weeks before the onset of ataxia. The expression of the toxic protein first caused a reduction of Purkinje cells intrinsic excitability, which was followed by atrophy of Purkinje cells dendrite arborization and aberrant glutamatergic signalling, finally leading to disruption of Purkinje cells innervation of climbing fibres and loss of intrinsic plasticity of Purkinje cells. Functionally, we found that deficits in eyeblink conditioning, a form of cerebellum-dependent motor learning, precede the onset of ataxia, matching the timeline of climbing fibre degeneration and reduced intrinsic plasticity. Together, our results suggest that abnormal synaptic signalling and intrinsic plasticity during the pre-ataxia stage of spinocerebellar ataxias underlie an aberrant cerebellar circuitry that anticipates the full extent of the disease severity. Furthermore, our work indicates the potential for eyeblink conditioning to be used as a sensitive tool to detect early cerebellar dysfunction as a sign of future disease.

Progression of Clinical and Eye Movement Markers in Preataxic Carriers of Machado-Joseph Disease

BACKGROUND

Little is known about preclinical stages of Machado-Joseph disease, a polyglutamine disorder characterized by progressive adult-onset ataxia.

OBJECTIVE

We aimed to describe the longitudinal progression of clinical and oculomotor variables in the preataxic phase of disease.

METHODS

Carriers and noncarriers were assessed at three visits. Preataxic carriers (Scale for Assessment and Rating of Ataxia score < 3) expected to start ataxia in ≤4 years were considered near onset (PAN). Progressions of ataxic and preataxic carriers, considering status at the end of the study, were described according to the start (or its prediction) of gait ataxia (TimeToAfterOnset) and according to the study time.

RESULTS

A total of 35 ataxics, 38 preataxics, and 22 noncarriers were included. The "TimeToAfterOnset" timeline showed that Neurological Examination Scale for Spinocerebellar Ataxias (NESSCA; effect size, 0.09), Inventory of Non-Ataxia Symptoms (INAS0.07), and the vestibulo-ocular reflex gain (0.12) progressed in preataxic carriers, and that most slopes accelerate in PAN, turning similar to those of ataxics. In the study time, NESSCA (1.36) and vertical pursuit gain (1.17) significantly worsened in PAN, and 6 of 11 PANs converted to ataxia. For a clinical trial with 80% power and 2-year duration, 57 PANs are needed in each study arm to detect a 50% reduction in the conversion rate.

CONCLUSIONS

NESSCA, INAS, vestibulo-ocular reflex, and vertical pursuit gains significantly worsened in the preataxic phase. The "TimeToAfterOnset" timeline unveiled that slopes of most variables are small in preataxics but increase and reach the ataxic slopes from 4 years before the onset of ataxia. For future trials in preataxic carriers, we recommend recruiting PANs and using the conversion rate as the primary outcome. © 2022 International Parkinson and Movement Disorder Society.

Altered brain white matter structural motor network in spinocerebellar ataxia type 3

OBJECTIVES

Spinocerebellar ataxia type 3 is a disorder within the brain network. However, the relationship between the brain network and disease severity is still unclear. This study aims to investigate changes in the white matter (WM) structural motor network, both in preclinical and ataxic stages, and its relationship with disease severity.

METHODS

For this study, 20 ataxic, 20 preclinical SCA3 patients, and 20 healthy controls were recruited and received MRI scans. Disease severity was quantified using the SARA and ICARS scores. The WM motor structural network was created using probabilistic fiber tracking and was analyzed using graph theory and network-based statistics at global, nodal, and edge levels. In addition, the correlations between network topological measures and disease duration or clinical scores were analyzed.

RESULTS

Preclinical patients showed increasing assortativity of the motor network, altered subnetwork including 12 edges of 11 nodes, and 5 brain regions presenting reduced nodal strength. In ataxic patients assortativity of the motor network also increased, but global efficiency, global strength, and transitivity decreased. Ataxic patients showed a wider altered subnetwork and a higher number of reduced nodal strengths. A negative correlation between the transitivity of the motor network and SARA and ICARS scores was observed in ataxic patients.

INTERPRETATION

Changes to the WM motor network in SCA3 start before ataxia onset, and WM motor network involvement increases with disease progression. Global network topological measures of the WM motor network appear to be a promising image biomarker for disease severity. This study provides new insights into the pathophysiology of disease in SCA3/MJD.

OUP accepted manuscript

Spinocerebellar ataxias consist of a highly heterogeneous group of inherited movement disorders clinically characterized by progressive cerebellar ataxia variably associated with additional distinctive clinical signs. The genetic heterogeneity is evidenced by the myriad of associated genes and underlying genetic defects identified. In this study, we describe a new spinocerebellar ataxia subtype in nine members of a Spanish five-generation family from Menorca with affected individuals variably presenting with ataxia, nystagmus, dysarthria, polyneuropathy, pyramidal signs, cerebellar atrophy and distinctive cerebral demyelination. Affected individuals presented with horizontal and vertical gaze-evoked nystagmus and hyperreflexia as initial clinical signs, and a variable age of onset ranging from 12 to 60 years. Neurophysiological studies showed moderate axonal sensory polyneuropathy with altered sympathetic skin response predominantly in the lower limbs. We identified the c.1877C > T (p.Ser626Leu) pathogenic variant within the SAMD9L gene as the disease causative genetic defect with a significant log-odds score (Z_max = 3.43; θ = 0.00; P < 3.53 × 10⁻⁵). We demonstrate the mitochondrial location of human SAMD9L protein, and its decreased levels in patients’ fibroblasts in addition to mitochondrial perturbations. Furthermore, mutant SAMD9L in zebrafish impaired mobility and vestibular/sensory functions. This study describes a novel spinocerebellar ataxia subtype caused by SAMD9L mutation, SCA49, which triggers mitochondrial alterations pointing to a role of SAMD9L in neurological motor and sensory functions.

Nystagmus may be the first neurological sign in early stages of spinocerebellar ataxia type 3

BACKGROUND

Spinocerebellar ataxia type 3 (SCA3) is the most common autosomal dominant spinocerebellar ataxia worldwide. Almost all patients with SCA3 exhibit nystagmus and/or saccades impairment.

OBJECTIVE

To investigate the presence of nystagmus as an early neurological manifestation, before ataxia, in some patients with SCA3 in the first six months of the disease.

METHODS

We evaluated a series of 155 patients with clinically and molecularly proven SCA3 between 2013 and 2020. Data regarding sex, age, age at onset, disease duration, CAG repeat expansion length, first symptom, presence of ataxia, scores on SARA and ICARS scales, and presence and characteristics of nystagmus were collected.

RESULTS

We identified seven patients with symptomatic SCA3 who presented with isolated nystagmus. In these seven individuals the age at onset ranged from 24 to 57 years, and disease duration from four to six months.

CONCLUSIONS

Our study showed that nystagmus may be the first neurological sign in SCA3. This clinical observation reinforces the idea that the neurodegenerative process in SCA3 patients may start in vestibular system connections or in flocculonodular lobe. This study adds relevant information about pre-symptomatic features in SCA3 that may work as basis for a better understanding of brain degeneration and for future therapeutic clinical trials.

Clinical, Imaging, and Laboratory Markers of Premanifest Spinocerebellar Ataxia 1, 2, 3, and 6: A Systematic Review

Background and Purpose

Premanifest mutation carriers with spinocerebellar ataxia (SCA) can exhibit subtle abnormalities before developing ataxia. We summarized the preataxic manifestations of SCA1, -2, -3, and -6, and their associations with ataxia onset.

Methods

We included studies of the premanifest carriers of SCA published between January 1998 and December 2019 identified in Scopus and PubMed by searching for terms including ‘spinocerebellar ataxia’ and several synonyms of ‘preataxic manifestation’. We systematically reviewed the results obtained in studies categorized based on clinical, imaging, and laboratory markers.

Results

We finally performed a qualitative analysis of 48 papers. Common preataxic manifestations appearing in multiple SCA subtypes were muscle cramps, abnormal muscle reflexes, instability in gait and posture, lower Composite Cerebellar Functional Severity scores, abnormalities in video-oculography and transcranial magnetic stimulation, and gray-matter loss and volume reduction in the brainstem and cerebellar structures. Also, decreased sensory amplitudes in nerve conduction studies were observed in SCA2. Eotaxin and neurofilament light-chain levels were revealed as sensitive blood biomarkers in SCA3. Concerning potential predictive markers, hyporeflexia and abnormalities of somatosensory evoked potentials showed correlations with the time to ataxia onset in SCA2 carriers. However, no longitudinal data were found for the other SCA gene carriers.

Conclusions

Our results suggest that preataxic manifestations vary among SCA1, -2, -3, and -6, with some subtypes sharing specific features. Combining various markers into a standardized index for premanifest carriers may be useful for early screening and assessing the risk of disease progression in SCA carriers.

Establish a Nomogram to Predict Falls in Spinocerebellar Ataxia Type 3

Purpose: Falls are common and are frequently accompanied by injuries in patients with spinocerebellar ataxias type 3 (SCA3). We explored which factors could predict falls in a cohort of patients with SCA3 and developed a nomogram model to predict the first fall in non-fallen patients with SCA3. Method: We conducted a prospective cohort study. Forty-four non-fallen patients with SCA3 were followed up until the first fall or November 5, 2020, whichever came first. Univariate and multivariate Cox proportional hazard regression analyses were applied to explore the predictive factors of falls in patients with SCA3. A nomogram model predicting the no-fall probabilities at 3, 6, 12, and 24 months was formulated based on the results of the multivariate Cox analysis. Internal validation was conducted to assess the discrimination and calibration of the final model using bootstrapping with 1,000 resamples. Results: Multivariate Cox proportional hazard regression showed that the presence of dystonia, hyperreflexia, urinary incontinence, and hidrosis and the number of abnormal eye movements predicted a more rapid progression to falls in patients with SCA3. The nomogram model showed good discrimination with a concordance index of 0.83 and good calibration. Conclusion: Patients with dystonia, hyperreflexia, urinary incontinence, and hidrosis, and more types of abnormal eye movement had a more rapid progression to falls in SCA3.

Abnormal eye movements in spinocerebellar ataxia type 3

Background

Abnormal eye movements are common in spinocerebellar ataxias Type 3 (SCA3). We conducted the research to explore the frequency of abnormal eye movements in Chinese patients with SCA3, to compare the demographic and clinical characteristics between SCA3 patients with and without each type of abnormal eye movement, and to explore the correlation between abnormal eye movements and the severity of ataxia.

Methods

Seventy-four patients with SCA3 were enrolled in this cross-sectional study. Six types of abnormal eye movements including impaired smooth pursuit, increased square-wave jerks (SWJ), gaze-evoked nystagmus (GEN), slowing of saccades, saccadic hypo/hypermetria and supranuclear gaze palsy were evaluated by experienced neurologists. The severity of ataxia was evaluated by Scale for the Assessment and Rating of Ataxia (SARA).

Results

The prevalence of impaired smooth pursuit, increased SWJ, GEN, slowing of saccades, saccadic hypo/hypermetria and supranuclear gaze palsy in Chinese SCA3 patients was 28.4, 13.5, 78.4, 41.9, 23.0, and 5.4%, respectively. SCA3 patients with GEN had higher scores of International Cooperative Ataxia Rating Scale (ICARS-IV) and total ICARS, and longer length of CAG repeat than patients without GEN. SCA3 patients with slowing of saccades had a longer disease duration, higher scores of ICARS-I, ICARS-II, total ICARS and SARA than patients without slowing of saccades. SCA3 patients with saccadic hypo/hypermetria had higher scores of ICARS-III, ICARS-IV, and SARA than patients without saccadic hypo/hypermetria. The demographic and clinical characteristics did not differ significantly between SCA3 patients with and without impaired smooth pursuit, increased SWJ, or supranuclear gaze palsy. Multivariate linear regression showed that the number of abnormal eye movements (0–6), disease duration, Hamilton Depression Rating Scale-24 (HDRS-24) score, and CAG repeat length were positively correlated with SARA score, whereas Montreal Cognitive Assessment (MoCA) score was negatively correlated with SARA score in SCA3.

Conclusions

An increased number of abnormal eye movement types correlated with the severity of ataxia in SCA3.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02057-3.

Pre-ataxic Changes of Clinical Scales and Eye Movement in Machado-Joseph Disease: BIGPRO Study

BACKGROUND

The pathological burden of spinocerebellar ataxia type 3, also known as Machado-Joseph disease (SCA3/MJD), accumulates before the beginning of symptoms. Our study aims at validating biomarkers for disease progression since pre-ataxic periods. We report on baseline findings of clinical scales and oculomotor neurophysiology.

METHODS

Ataxic (Scale for the Assessment and Rating of Ataxia > 2.5) and at 50% risk subjects were included. The latter were subdivided into noncarriers, pre-ataxic carriers near (PAN), or pre-ataxic carriers far from (PAFF) ataxia onset (AO), with 4 years from the predicted age at onset being the cutoff. The subjects were assessed by Neurological Examination Score for Spinocerebellar Ataxia (NESSCA), International Cooperative Ataxia Rating Scale (ICARS), Inventory of Non-Ataxic Signs (INAScount), Composite Cerebellar Functions Score and SCA Functional Index, and video-oculography, including the regression slope of vestibulo-ocular reflex gain (VORr), main sequence of volitional and reflexive vertical saccades, slow-phase velocity of central and gaze-evoked (SPV-GE) nystagmus, and vertical pursuit gain. Correction for multiple comparisons was performed; the threshold for statistical significance was P < 0.05.

RESULTS

A total of 35 ataxic, 14 PAN, 24 PAFF, and 22 noncarriers were included. All variables showed significant differences between groups and correlated to time to onset or time after onset, among all 73 SCA3/MJD carriers; none significantly changed with age in controls. NESSCA, ICARS, INAScount, VORr, main sequence of volitional saccades, and SPV-GE not only distinguished PAN from controls but also correlated with time left to AO.

CONCLUSIONS

Clinical scales and video-oculography variables were already altered in pre-ataxic SCA3/MJD carriers and worsened with time. NESSCA, ICARS, INAScount, VORr, main sequence of vertical volitional saccades, and SPV-GE are good candidates to measure preclinical changes in SCA3/MJD. © 2021 International Parkinson and Movement Disorder Society.

Accurate detection of cerebellar smooth pursuit eye movement abnormalities via mobile phone video and machine learning

Eye movements are disrupted in many neurodegenerative diseases and are frequent and early features in conditions affecting the cerebellum. Characterizing eye movements is important for diagnosis and may be useful for tracking disease progression and response to therapies. Assessments are limited as they require an in-person evaluation by a neurology subspecialist or specialized and expensive equipment. We tested the hypothesis that important eye movement abnormalities in cerebellar disorders (i.e., ataxias) could be captured from iPhone video. Videos of the face were collected from individuals with ataxia (n = 102) and from a comparative population (Parkinson's disease or healthy participants, n = 61). Computer vision algorithms were used to track the position of the eye which was transformed into high temporal resolution spectral features. Machine learning models trained on eye movement features were able to identify abnormalities in smooth pursuit (a key eye behavior) and accurately distinguish individuals with abnormal pursuit from controls (sensitivity = 0.84, specificity = 0.77). A novel machine learning approach generated severity estimates that correlated well with the clinician scores. We demonstrate the feasibility of capturing eye movement information using an inexpensive and widely accessible technology. This may be a useful approach for disease screening and for measuring severity in clinical trials.

Ophthalmic Manifestations and Genetics of the Polyglutamine Autosomal Dominant Spinocerebellar Ataxias: A Review

Spinocerebellar ataxia (SCA) is a part of the cerebellar neurodegenerative disease group that is diverse in genetics and phenotypes. It usually shows autosomal dominant inheritance. SCAs, always together with the cerebellar degeneration, may exhibit clinical deficits in brainstem or eye, especially retina or optic nerve. Interestingly, autosomal dominant SCAs share a common genetic mechanism; the length of the glutamine chain is abnormally expanded due to the increase in the cytosine–adenine–guanine (CAG) repeats of the disease causing gene. Studies have suggested that the mutant ataxin induces alteration of protein conformation and abnormal aggregation resulting in nuclear inclusions, and causes cellular loss of photoreceptors through a toxic effect. As a result, these pathologic changes induce a downregulation of genes involved in the phototransduction, development, and differentiation of photoreceptors such as CRX, one of the photoreceptor transcription factors. However, the exact mechanism of neuronal degeneration by mutant ataxin restricted to only certain type of neuronal cell including cerebellar Purkinje neurons and photoreceptor is still unclear. The most common SCAs are types 1, 2, 3, 6, 7, and 17 which contain about 80% of autosomal dominant SCA cases. Various aspects of eye movement abnormalities are evident depending on the degree of cerebellar and brainstem degeneration in SCAs. In addition, certain types of SCAs such as SCA7 are characterized by both cerebellar ataxia and visual loss mainly due to retinal degeneration. The severity of the retinopathy can vary from occult macular photoreceptor disruption to extensive retinal atrophy and is correlated with the number of CAG repeats. The value of using optical coherence tomography in conjunction with electrodiagnostic and genetic testing is emphasized as the combination of these tests can provide critical information regarding the etiology, morphological evaluation, and functional significances. Therefore, ophthalmologists need to recognize and differentiate SCAs in order to properly diagnose and evaluate the disease. In this review, we have described and discussed SCAs showing ophthalmic abnormalities with particular attention to their ophthalmic features, neurodegenerative mechanisms, genetics, and future perspectives.

Eye Movement Abnormalities Are Ubiquitous in the Spinocerebellar Ataxias

Oculomotor abnormalities are common in the spinocerebellar ataxias (SCAs). In studies of SCAs 1, 2, 3, and 6, eye movement abnormalities correlate with disease severity. Oculomotor abnormalities may be the sole motor manifestation of early and/or premanifest disease; however, not all ataxia rating scales include oculomotor assessment. We sought to identify the prevalence and characteristics of oculomotor abnormalities at first presentation in a large SCA cohort, including those in earlier stages of disease. We performed a retrospective assessment of initial clinical examinations of SCA patients followed in the Massachusetts General Hospital Ataxia Unit and assessed with the Brief Ataxia Rating Scale (BARS). One hundred thirty-four SCA patients were assessed: 17 SCA1, 13 SCA2, 55 SCA3, 2 SCA5, 22 SCA6, 11 SCA7, 9 SCA8, and 5 SCA17, mainly in the early stages of disease (67.2% stage 0-1). Oculomotor abnormalities were present on initial assessment in 94.8%, including 7/9 stage 0 and 77/81 stage 1 patients. Stage 0/1 patients had frequent saccadic intrusions, nystagmus, and hypo/hypermetric saccades. Saccadic slowing was present even in early stage SCA7 and SCA2, eventually leading to ophthalmoplegia. The burden of oculomotor abnormalities correlated with disease stage, duration, and severity, remaining highly significant even when controlling for age. The ubiquitous presence of oculomotor abnormalities in the SCAs, particularly early in the course, underscores the importance of oculomotor assessment in ataxia rating scales such as BARS. These findings highlight the potential for quantitative physiological oculomotor measures as clinical biomarkers in natural history studies and clinical trials.

Clinical, genetic and neuropathological characterization of spinocerebellar ataxia type 37

The autosomal dominant spinocerebellar ataxias (SCAs) consist of a highly heterogeneous group of rare movement disorders characterized by progressive cerebellar ataxia variably associated with ophthalmoplegia, pyramidal and extrapyramidal signs, dementia, pigmentary retinopathy, seizures, lower motor neuron signs, or peripheral neuropathy. Over 41 different SCA subtypes have been described evidencing the high clinical and genetic heterogeneity. We previously reported a novel spinocerebellar ataxia type subtype, SCA37, linked to an 11-Mb genomic region on 1p32, in a large Spanish ataxia pedigree characterized by ataxia and a pure cerebellar syndrome distinctively presenting with early-altered vertical eye movements. Here we demonstrate the segregation of an unstable intronic ATTTC pentanucleotide repeat mutation within the 1p32 5' non-coding regulatory region of the gene encoding the reelin adaptor protein DAB1, implicated in neuronal migration, as the causative genetic defect of the disease in four Spanish SCA37 families. We describe the clinical-genetic correlation and the first SCA37 neuropathological findings caused by dysregulation of cerebellar DAB1 expression. Post-mortem neuropathology of two patients with SCA37 revealed severe loss of Purkinje cells with abundant astrogliosis, empty baskets, occasional axonal spheroids, and hypertrophic fibres by phosphorylated neurofilament immunostaining in the cerebellar cortex. The remaining cerebellar Purkinje neurons showed loss of calbindin immunoreactivity, aberrant dendrite arborization, nuclear pathology including lobulation, irregularity, and hyperchromatism, and multiple ubiquitinated perisomatic granules immunostained for DAB1. A subpopulation of Purkinje cells was found ectopically mispositioned within the cerebellar cortex. No significant neuropathological alterations were identified in other brain regions in agreement with a pure cerebellar syndrome. Importantly, we found that the ATTTC repeat mutation dysregulated DAB1 expression and induced an RNA switch resulting in the upregulation of reelin-DAB1 and PI3K/AKT signalling in the SCA37 cerebellum. This study reveals the unstable ATTTC repeat mutation within the DAB1 gene as the underlying genetic cause and provides evidence of reelin-DAB1 signalling dysregulation in the spinocerebellar ataxia type 37.

State biomarkers for Machado Joseph disease: Validation, feasibility and responsiveness to change

Machado-Joseph disease (SCA3/MJD) is the most common spinocerebellar ataxia worldwide, and particularly so in Southern Brazil. Due to an expanded polyglutamine at ataxin-3, SCA3/MJD presents a relentless course with no current disease modifying treatment. Clinical scales used to measure SCA3/MJD progression present moderate effect sizes, a major drawback for their use as main outcomes in clinical trials, given the rarity and slow progression of the disease. This limitation might be overcome by finding good surrogate markers. We present here a review of studies on peripheral and neurophysiological markers in SCA3/MJD that can be candidates for state biomarkers. Data on markers already studied were summarized, giving emphasis on validation against clinical scale, and responsiveness to change. While some biological fluid compounds and neurophysiological parameters showed poor responsiveness, others seemed to be good candidates. Some potential candidates that are waiting for responsiveness studies were serum levels of neuron specific enolase, vestibulo-ocular reflex and video-oculography. Candidates evaluated by RNA and microRNA expression levels need further studies to improve their measurements. Data on peripheral levels of Beclin-1 and DNAJB1 are promising but still incipient. We conclude that several potential candidates should follow onto validating studies for surrogate state biomarkers of SCA3/MJD.

Abnormal Eye Movements in Parkinsonism and Movement Disorders

Abnormal eye movements are commonly observed in movement disorders. Ocular motility examination should include bedside evaluation and laboratory recording of ocular misalignment, involuntary eye movements, including nystagmus and saccadic intrusions/oscillations, triggered nystagmus, saccades, smooth pursuit (SP), and the vestibulo-ocular reflex. Patients with Parkinson's disease (PD) mostly show hypometric saccades, especially for the selfpaced saccades, and impaired SP. Early vertical saccadic palsy is characteristic of progressive supranuclear palsy-Richardson's syndrome. Patients with cortico-basal syndrome typically show a delayed onset of saccades. Downbeat and gaze-evoked nystagmus and hypermetric saccades are characteristic ocular motor findings in ataxic disorders due to cerebellar dysfunction. In this review, we discuss various ocular motor findings in movement disorders, including PD and related disorders, ataxic syndromes, and hyperkinetic movement disorders. Systemic evaluation of the ocular motor functions may provide valuable information for early detection and monitoring of movement disorders, despite an overlap in the abnormal eye movements among different movement disorders.

Recent advances in understanding dominant spinocerebellar ataxias from clinical and genetic points of view

Abstract

Spinocerebellar ataxias (SCAs) are rare types of cerebellar ataxia with a dominant mode of inheritance. To date, 47 SCA subtypes have been identified, and the number of genes implicated in SCAs is continually increasing. Polyglutamine (polyQ) expansion diseases

( ATXN1/SCA1, ATXN2/SCA2, ATXN3/SCA3, CACNA1A/SCA6, ATXN7/SCA7, TBP/SCA17, and ATN1/DRPLA) are the most common group of SCAs. No preventive or curative treatments are currently available, but various therapeutic approaches, including RNA-targeting treatments, such as antisense oligonucleotides (ASOs), are being developed. Clinical trials of ASOs in SCA patients are already planned. There is, therefore, a need to identify valid outcome measures for such studies. In this review, we describe recent advances towards identifying appropriate biomarkers, which are essential for monitoring disease progression and treatment efficacy. Neuroimaging biomarkers are the most powerful markers identified to date, making it possible to reduce sample sizes for clinical trials. Changes on brain MRI are already evident at the premanifest stage in SCA1 and SCA2 carriers and are correlated with CAG repeat size. Other potential biomarkers have also been developed, based on neurological examination, oculomotor study, cognitive assessment, and blood and cerebrospinal fluid analysis. Longitudinal studies based on multimodal approaches are required to establish the relationships between parameters and to validate the biomarkers identified.

Oculomotor deficits in spinocerebellar ataxia type 3: Potential biomarkers of preclinical detection and disease progression

AIMS

To detect specific oculomotor deficits in preclinical stage of spinocerebellar ataxia type 3 (SCA3) and evaluate whether these abnormalities prove useful as potential biomarkers of disease progression.

METHODS

A Chinese cohort of 56 patients with SCA3, including 12 preclinical carriers of SCA3 (pre-SCA3) and 44 manifest SCA3, and 26 healthy control individuals were recruited. We performed a detailed investigation on central oculomotor performance including fixation, gaze, smooth pursuit, prosaccade, and antisaccade using video-oculography.

RESULTS

Common oculomotor features of pre-SCA3 included square-wave jerk during central fixation and gaze holding, impaired vertical smooth pursuit, slow upward saccade, and increased antisaccade error rate. In our SCA3 cohort, all oculomotor parameters were correlated with the score of the Scale for the Assessment and Rating of Ataxia, whilst some of them were correlated with disease duration.

CONCLUSION

This study showed that a series of neuropathological changes reflected by oculomotor abnormalities appeared preferentially in preclinical stage of SCA3. Accordingly, objective oculomotor preclinical signs may be useful to detect the optimum time-point for therapeutic interventions in future clinical trials of SCA3. Larger and longitudinal data are warranted to confirm our results.

Individual changes in preclinical spinocerebellar ataxia identified via increased motor complexity

BACKGROUND

Movement changes in autosomal-dominant spinocerebellar ataxias are suggested to occur many years before clinical manifestation. Detecting and quantifying these changes in the preclinical phase offers a window for future treatment interventions and allows the clinician to decipher the earliest dysfunctions starting the evolution of spinocerebellar ataxia. We hypothesized that quantitative movement analysis of complex stance and gait tasks allows to (i) reveal movement changes already at early stages of the preclinical phase when clinical ataxia signs are still absent and to (ii) quantify motor progression in this phase.

METHODS

A total of 46 participants (14 preclinical spinocerebellar ataxia mutation carriers [spinocerebellar ataxias 1,2,3,6], 9 spinocerebellar ataxia patients at an early stage; 23 healthy controls) were assessed by quantitative movement analyses of increasingly complex stance and walking tasks in a cross-sectional design.

RESULTS

Body sway in stance and spatiotemporal variability in tandem walking differentiated between preclinical mutation carriers and healthy controls (P < .01). Complex movement conditions allowed one to discriminate even those mutation carriers without any clinical signs in posture and gait (SARA_posture&gait  = 0; P < .04). Multivariate regression analysis categorized preclinical mutation carriers on a single-subject level with 100% accuracy within a range of 10 years to the estimated onset. Movement features in stance and gait correlated significantly with genetically estimated time to onset, indicating a gradual increase of motor changes with increasing proximity to disease manifestation.

CONCLUSION

Our results provide evidence for subclinical motor changes in spinocerebellar ataxia, which allow to discriminate patients without clinical signs even on a single-subject basis and may help capture disease progression in the preclinical phase. © 2016 International Parkinson and Movement Disorder Society.

Population genetics and new insight into range of CAG repeats of spinocerebellar ataxia type 3 in the Han Chinese population

Spinocerebellar ataxia type 3 (SCA3), also called Machado-Joseph disease (MJD), is one of the most common SCAs worldwide and caused by a CAG repeat expansion located in ATXN3 gene. Based on the CAG repeat numbers, alleles of ATXN3 can be divided into normal alleles (ANs), intermediate alleles (AIs) and expanded alleles (AEs). It was controversial whether the frequency of large normal alleles (large ANs) is related to the prevalence of SCA3 or not. And there were huge chaos in the comprehension of the specific numbers of the range of CAG repeats which is fundamental for genetic analysis of SCA3. To illustrate these issues, we made a novel CAG repeat ladder to detect CAG repeats of ATXN3 in 1003 unrelated Chinese normal individuals and studied haplotypes defined by three single nucleotide polymorphisms (SNPs) closed to ATXN3. We found that the number of CAG repeats ranged from 13 to 49, among them, 14 was the most common number. Positive skew, the highest frequency of large ANs and 4 AIs which had never been reported before were found. Also, AEs and large ANs shared the same haplotypes defined by the SNPs. Based on these data and other related studies, we presumed that de novo mutations of ATXN3 emerging from large ANs are at least one survival mechanisms of mutational ATXN3 and we can redefine the range of CAG repeats as: ANs≤44, 45 ≤AIs ≤49 and AEs≥50.

Lysosomal storage disease in the brain: mutations of the β-mannosidase gene identified in autosomal dominant nystagmus

PURPOSE

Genetic etiology of congenital/infantile nystagmus remains largely unknown. This study aimed to identify genomic mutations in patients with infantile nystagmus and an associated disease network.

METHODS

Patients with inherited and sporadic infantile nystagmus were recruited for whole-exome and Sanger sequencing. β-Mannosidase activities were measured. Gene expression, protein-protein interaction, and nystagmus-associated lysosomal storage disease (LSD) genes were analyzed.

RESULTS

A novel heterozygous mutation (c.2013G>A; p.R638H) of MANBA, which encodes lysosomal β-mannosidase, was identified in patients with autosomal-dominant nystagmus. An additional mutation (c.2346T>A; p.L749H) in MANBA was found by screening patients with sporadic nystagmus. MANBA was expressed in the pretectal nucleus of the developing midbrain, known to be involved in oculomotor and optokinetic nystagmus. Functional validation of these mutations demonstrated a significant decrease of β-mannosidase activities in the patients as well as in mutant-transfected HEK293T cells. Further analysis revealed that nystagmus is present in at least 24 different LSDs involving the brain.

CONCLUSION

This is the first identification of MANBA mutations in patients with autosomal-dominant nystagmus, suggesting a new clinical entity. Because β-mannosidase activities are required for development of the oculomotor nervous system, our findings shed new light on the role of LSD-associated genes in the pathogenesis of infantile nystagmus.