Slow saccades in cerebellar disease

A comprehensive review of iPS cell line-based disease modelling of the polyglutamine spinocerebellar ataxias 2 and 3: a focus on the research outcomes

Spinocerebellar ataxias (SCAs) are a rare autosomal dominant neurodegenerative disorder. To date, approximately 50 different subtypes of SCAs have been characterized. The prevalent types of SCAs are usually of PolyQ origin, wherein the disease pathology is a consequence of multiple glutamine residues being encoded onto the disease proteins, causing expansions. SCAs 2 and 3 are the most frequently diagnosed subtypes, wherein affected patients exhibit certain characteristic physiological manifestations, such as gait ataxia and dysarthria. Nevertheless, other clinical signs were exclusive to these subtypes. Recently, multiple molecular diagnostic methods have been developed to identify and characterize these subtypes. Despite these advancements, the molecular pathology of SCAs remains unknown. To further understand the mechanisms involved in neurodegenerative SCAs 2 and 3, patient-derived induced pluripotent stem cell (iPSC)-based modelling is a compelling avenue to pursue. We cover the present state of iPSC-based in-vitro illness modelling of SCA subtypes 2 and 3 below, along with a list of cell lines created, and the relevance of research outcomes to personalized autologous therapy.

Quantification of saccadic fatigability and diagnostic efficacy for myasthenia gravis

BACKGROUND AND OBJECTIVES

The diagnostic challenge of myasthenia gravis (MG) is exacerbated by the variable efficacy of current testing methodologies, necessitating innovative approaches to accurately identify the condition. This study aimed to assess ocular muscle fatigue in patients with MG using video-oculography (VOG) by examining repetitive saccadic eye movements and comparing these metrics to those of healthy control participants.

METHODS

This prospective, cross-sectional study was conducted at a tertiary care center and involved 62 patients diagnosed with MG (48 with ocular MG and 14 with generalized MG) and a control group of 31 healthy individuals, matched for age and sex. The assessment involved recording saccadic eye movements within a ± 15° range, both horizontally and vertically, at a rate of 15 saccades per minute over a 5-min period, resulting in 75 cycles. Participants were afforded a 3-min rest interval between each set to mitigate cumulative fatigue. The primary outcome was the detection of oculomotor fatigue, assessed through changes in saccadic waveforms, range, peak velocity, latency, and the duration from onset to target, with a focus on comparing the second saccade against the average of the last five saccades.

RESULTS

In the evaluation of repetitive saccadic movements, patients with MG exhibited a reduced saccadic range and a prolonged duration to reach the target, compared to healthy subjects. Furthermore, a significant elevation in the frequency of multistep saccades was observed among MG patients, with a marked rise observed over consecutive trials. Receiver operating characteristic (ROC) analysis revealed the discriminative performance of multistep saccade frequency, in conjunction with variations in saccadic range and duration from onset to target achievement between the second saccade and the mean of the final five saccades, as effective in distinguishing MG patients from healthy subjects. Although alterations in peak saccadic velocity and latency were less pronounced, they were nevertheless detectable.

DISCUSSION

The utilization of VOG for repetitive saccadic testing in the diagnosis of MG has demonstrated considerable diagnostic precision. This methodology affords significant accuracy in evaluating ocular muscle fatigue in MG patients, providing class III evidence supportive of its clinical application.

Video-Oculography Assessment in Neurodegenerative Ataxias and Niemann Pick Type C

Introduction

Deceleration of vertical saccades, an early and characteristic finding of Niemann-Pick Type C (NP-C), may help diagnosis. Our aim in this study was to demonstrate the role of video-oculography (VOG), in the differential diagnosis of ataxia syndromes, particularly of NP-C, using this technique in the evaluation of saccadic velocity and smooth pursuit gain of ataxia patients.

Methods

We recruited consecutive 50 ataxia patients and 50 healthy control subjects who were age and sex-matched with the patient group. Saccadic eye movements and smooth pursuit eye movements for different angles and different directions from patients and healthy subjects were recorded by using VOG.

Results

Saccadic eye movement velocity and smooth pursuit gain values of the patients were significantly lower in all directions and at all angles as compared to healthy subjects. In the patient group, 3 cases out of 50 were selected as suspected NP-C, based on the dissociation between their markedly impaired vertical saccadic velocity and near normal to slightly impaired horizontal one and relatively intact smooth pursuit eye movements; the diagnoses in all 3 cases were confirmed with positive genetic testing, and thereupon Miglustat treatment was started.

Conclusion

Our findings support that cerebellar pathology in degenerative ataxia patients is associated with both impaired saccadic velocity and smooth pursuit gain, whereas in NP-C, only the impaired vertical saccades as opposed to relatively preserved other eye movements are seemingly a diagnostic marker for the entity. We conclude that recording of eye movements could be useful for differential diagnosis and monitorization of the treatment of ataxia syndromes as an easy and objective method.

Quantitative Oculomotor Assessment in Hereditary Ataxia: Discriminatory Power, Correlation with Severity Measures, and Recommended Parameters for Specific Genotypes

Characterizing bedside oculomotor deficits is a critical factor in defining the clinical presentation of hereditary ataxias. Quantitative assessments are increasingly available and have significant advantages, including comparability over time, reduced examiner dependency, and sensitivity to subtle changes. To delineate the potential of quantitative oculomotor assessments as digital-motor outcome measures for clinical trials in ataxia, we searched MEDLINE for articles reporting on quantitative eye movement recordings in genetically confirmed or suspected hereditary ataxias, asking which paradigms are most promising for capturing disease progression and treatment response. Eighty-nine manuscripts identified reported on 1541 patients, including spinocerebellar ataxias (SCA2, n = 421), SCA3 (n = 268), SCA6 (n = 117), other SCAs (n = 97), Friedreich ataxia (FRDA, n = 178), Niemann-Pick disease type C (NPC, n = 57), and ataxia-telangiectasia (n = 85) as largest cohorts. Whereas most studies reported discriminatory power of oculomotor assessments in diagnostics, few explored their value for monitoring genotype-specific disease progression (n = 2; SCA2) or treatment response (n = 8; SCA2, FRDA, NPC, ataxia-telangiectasia, episodic-ataxia 4). Oculomotor parameters correlated with disease severity measures including clinical scores (n = 18 studies (SARA: n = 9)), chronological measures (e.g., age, disease duration, time-to-symptom onset; n = 17), genetic stratification (n = 9), and imaging measures of atrophy (n = 5). Recurrent correlations across many ataxias (SCA2/3/17, FRDA, NPC) suggest saccadic eye movements as potentially generic quantitative oculomotor outcome. Recommendation of other paradigms was limited by the scarcity of cross-validating correlations, except saccadic intrusions (FRDA), pursuit eye movements (SCA17), and quantitative head-impulse testing (SCA3/6). This work aids in understanding the current knowledge of quantitative oculomotor parameters in hereditary ataxias, and identifies gaps for validation as potential trial outcome measures in specific ataxia genotypes.

Spatial and Temporal Abnormalities of Spontaneous Fixational Saccades and Their Correlates With Positive and Cognitive Symptoms in Schizophrenia

BACKGROUND AND HYPOTHESIS

Visual fixation is a dynamic process, with the spontaneous occurrence of microsaccades and macrosaccades. These fixational saccades are sensitive to the structural and functional alterations of the cortical-subcortical-cerebellar circuit. Given that dysfunctional cortical-subcortical-cerebellar circuit contributes to cognitive and behavioral impairments in schizophrenia, we hypothesized that patients with schizophrenia would exhibit abnormal fixational saccades and these abnormalities would be associated with the clinical manifestations.

STUDY DESIGN

Saccades were recorded from 140 drug-naïve patients with first-episode schizophrenia and 160 age-matched healthy controls during ten separate trials of 6-second steady fixations. Positive and negative symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). Cognition was assessed using the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB).

STUDY RESULTS

Patients with schizophrenia exhibited fixational saccades more vertically than controls, which was reflected in more vertical saccades with angles around 90° and a greater vertical shift of horizontal saccades with angles around 0° in patients. The fixational saccades, especially horizontal saccades, showed longer durations, faster peak velocities, and larger amplitudes in patients. Furthermore, the greater vertical shift of horizontal saccades was associated with higher PANSS total and positive symptom scores in patients, and the longer duration of horizontal saccades was associated with lower MCCB neurocognitive composite, attention/vigilance, and speed of processing scores. Finally, based solely on these fixational eye movements, a K-nearest neighbors model classified patients with an accuracy of 85%. Conclusions: Our results reveal spatial and temporal abnormalities of fixational saccades and suggest fixational saccades as a promising biomarker for cognitive and positive symptoms and for diagnosis of schizophrenia.

Psychiatric-Like Impairments in Mouse Models of Spinocerebellar Ataxias

Many patients with spinocerebellar ataxia (SCA) suffer from diverse neuropsychiatric issues, including memory impairments, apathy, depression, or anxiety. These neuropsychiatric aspects contribute per se to the reduced quality of life and worse prognosis. However, the extent to which SCA-related neuropathology directly contributes to these issues remains largely unclear. Behavioral profiling of various SCA mouse models can bring new insight into this question. This paper aims to synthesize recent findings from behavioral studies of SCA patients and mouse models. The role of SCA neuropathology for shaping psychiatric-like impairments may be exemplified in mouse models of SCA1. These mice evince robust cognitive impairments which are shaped by both the cerebellar as well as out-of-cerebellar pathology. Although emotional-related alternations are also present, they seem to be less robust and more affected by the specific distribution and character of the neuropathology. For example, cerebellar-specific pathology seems to provoke behavioral disinhibition, leading to seemingly decreased anxiety, whereas complex SCA1 neuropathology induces anxiety-like phenotype. In SCA1 mice with complex neuropathology, some of the psychiatric-like impairments are present even before marked cerebellar degeneration and ataxia and correlate with hippocampal atrophy. Similarly, complete or partial deletion of the implicated gene (Atxn1) leads to cognitive dysfunction and anxiety-like behavior, respectively, without apparent ataxia and cerebellar degeneration. Altogether, these findings collectively suggest that the neuropsychiatric issues have a biological basis partially independent of the cerebellum. As some neuropsychiatric issues may stem from weakening the function of the implicated gene, therapeutic reduction of its expression by molecular approaches may not necessarily mitigate the neuropsychiatric issues.

Optical coherence tomography as retinal imaging biomarker of neuroinflammation/neurodegeneration in systemic disorders in adults and children

The retina and the optic nerve are considered extensions of the central nervous system (CNS) and thus can serve as the window for evaluation of CNS disorders. Spectral domain optical coherence tomography (OCT) allows for detailed evaluation of the retina and the optic nerve. OCT can non-invasively document changes in single retina layer thickness and structure due to neuronal and retinal glial cells (RGC) modifications in systemic and local inflammatory and neurodegenerative diseases. These can include evaluation of retinal nerve fibre layer and ganglion cell complex, hyper-reflective retinal spots (HRS, sign of activated microglial cells in the retina), subfoveal neuroretinal detachment, disorganization of the inner retinal layers (DRIL), thickness and integrity of the outer retinal layers and choroidal thickness. This review paper will report the most recent data on the use of OCT as a non invasive imaging biomarker for evaluation of the most common systemic neuroinflammatory and neurodegenerative/neurocognitive disorders in the adults and in paediatric population. In the adult population the main focus will be on diabetes mellitus, multiple sclerosis, optic neuromyelitis, neuromyelitis optica spectrum disorders, longitudinal extensive transverse myelitis, Alzheimer and Parkinson diseases, Amyotrophic lateral sclerosis, Huntington's disease and schizophrenia. In the paediatric population, demyelinating diseases, lysosomal storage diseases, Nieman Pick type C disease, hypoxic ischaemic encephalopathy, human immunodeficiency virus, leukodystrophies spinocerebellar ataxia will be addressed.

ABC of Gaze and Ocular Oscillations

The chief goal of all eye movements is to maintain the image of an object steady on the retina especially the macula to preserve visual acuity. Gaze palsy refers to lack of the conjugate movements due to a failure of supranuclear control mechanisms. Supranuclear control is maintained by not one, but multiple eye movement systems and gaze mechanisms. Supranuclear gaze palsies can be associated with a myriad of aetiologies- from trauma or metabolic abnormalities to stroke, demyelinating disorders and space occupying lesions like tumours. Culprit lesions may be in frontal motor centres, brainstem gaze centres gaze or interconnecting segments. While the brainstem network for horizontal gaze lies in pons, that for vertical gaze is situated in midbrain. Further, ocular oscillations and nystagmus are abnormal eye movements that disrupt a steady fixation of gaze. It is prudent to be aware of various gaze pathways and their anatomical corelates in order to establish a topographic relationship of clinical findings. A systematic clinical examination may provide deep insights on the patho-physiological mechanisms along with aiding in localizing the lesion accurately. This review deals with systematic clinical approach to various gaze control systems.

Primary degeneration of oculomotor, motor, and somatosensory systems and auditory and visual pathways in spinocerebellar ataxia type 7: A clinicopathological study in a Japanese autopsy case

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant neurodegenerative disorder characterized by progressive cerebellar ataxia associated with retinal degeneration. The disease is rare in Japan, and this is the first full description of clinicopathological findings in a Japanese autopsy case of genetically confirmed SCA7 having 49 cytosine-adenine-guanine (CAG) trinucleotide repeats in the ataxin 7 gene. A 34-year-old Japanese man with no family history of clinically apparent neurodegenerative diseases presented with gait disturbance, gradually followed by truncal instability with progressive visual loss by the age of 42 years. He became wheelchair-dependent by 51 years old, neurologically exhibiting cerebellar ataxia, slow eye movement, slurred and scanning speech, lower limb spasticity, hyperreflexia, action-related slowly torsional dystonic movements in the trunk and limbs, diminished vibratory sensation in the lower limbs, auditory impairment, and macular degeneration. Brain magnetic resonance imaging revealed atrophy of the brainstem and cerebellum. He died of pneumonia at age 60 with a 26-year clinical duration of disease. Postmortem neuropathological examination revealed pronounced atrophy of the spinal cord, brainstem, cerebellum, external globus pallidus (GP), and subthalamic nucleus, microscopically showing neuronal cell loss and fibrillary astrogliosis with polyglutamine-immunoreactive neuronal nuclei and/or neuronal nuclear inclusions (NNIs). Degeneration was also accentuated in the oculomotor system, auditory and visual pathways, upper and lower motor neurons, and somatosensory system, including the spinal dorsal root ganglia. There was a weak negative correlation between the frequency of nuclear polyglutamine-positive neurons and the extent of neuronal cell loss. Clinicopathological features in the present case suggest that neurological symptoms, such as oculomotor, auditory, visual, and sensory impairments, are attributable to degeneration in their respective projection systems affected by SCA7 pathomechanisms and that dystonic movement is related to more significant degeneration in the external than internal GP.

Reading Warm-Up, Reading Skill, and Reading Prosody When Reading the My Grandfather Passage: An Exploratory Study Born Out of the Motor Planning Theory of Prosody and Reading Prosody Research

PURPOSE

The Motor Planning Theory of Prosody and reading prosody research indicate that "out of the blue" oral reading, as practiced in clinical and research settings, invokes surface rather than covert prosody, particularly when readers are recorded, less skilled, and/or speech impaired. Warm-up is not considered in passage reading for motor-speech assessment. We report on a preliminary study aimed to investigate the effect of warm-up on reading prosody in two conditions: silent reading alone and reading "out of the blue" followed by silent reading. A secondary aim of the study was to examine the effect of reading skill on reading prosody.

METHOD

Twenty-one monolingual, English-speaking volunteers were recorded reading the My Grandfather Passage (GP) while their eye movements were tracked. Participants were randomly assigned to one of two reading conditions: (a) silent-oral (SO) and (b) oral-silent-oral (OSO). In the SO condition, participants read the GP silently as a warm-up for the subsequent oral reading. In the OSO condition, participants first read the GP aloud ("out of the blue") and then read the same passage silently with the instruction to do this in preparation for a second oral reading. Reading skill was quantified using eye-voice span and Wide Range Achievement Test-Fourth Edition testing. Reading prosody was evaluated using pause indexes, the Acoustic Multidimensional Prosody Index, and speech rate.

CONCLUSIONS

One oral reading before a silent reading but not a silent reading alone before oral reading was shown to affect reading prosody. In terms of reading skill, results indicate that predictive associations patterned differently in the reading conditions explored, suggesting different underlying skill sets.

Eye Movement and Pupil Measures: A Review

Our subjective visual experiences involve complex interaction between our eyes, our brain, and the surrounding world. It gives us the sense of sight, color, stereopsis, distance, pattern recognition, motor coordination, and more. The increasing ubiquity of gaze-aware technology brings with it the ability to track gaze and pupil measures with varying degrees of fidelity. With this in mind, a review that considers the various gaze measures becomes increasingly relevant, especially considering our ability to make sense of these signals given different spatio-temporal sampling capacities. In this paper, we selectively review prior work on eye movements and pupil measures. We first describe the main oculomotor events studied in the literature, and their characteristics exploited by different measures. Next, we review various eye movement and pupil measures from prior literature. Finally, we discuss our observations based on applications of these measures, the benefits and practical challenges involving these measures, and our recommendations on future eye-tracking research directions.

Ocular Motor and Vestibular Characteristics of Antiglutamic Acid Decarboxylase-Associated Neurologic Disorders

BACKGROUND

Antiglutamic acid decarboxylase (GAD)-associated neurologic disorders are rare, with varied presentations, including stiff-person syndrome (SPS) and cerebellar ataxia (CA). Vestibular and ocular motor (VOM) dysfunction can be the main presentation in a subset of patients.

METHODS

Retrospective review of the Johns Hopkins Hospital medical records from 1997 to 2018 identified a total of 22 patients with a diagnosis of anti-GAD-associated SPS or CA who had detailed VOM assessments. Eight had prominent VOM dysfunction at the initial symptom onset and were referred to neurology from ophthalmology or otolaryngology ("early dominant"). Fourteen patients had VOM dysfunction that was not their dominant presentation and were referred later in their disease course from neurology to neuro-ophthalmology ("nondominant"). We reviewed clinical history, immunological profiles, and VOM findings, including available video-oculography.

RESULTS

In the 8 patients with early dominant VOM dysfunction, the average age of symptom onset was 53 years, and 5 were men. The most common symptom was dizziness, followed by diplopia. Seven had features of CA, and 4 had additional features of SPS. None had a structural lesion on brain MRI accounting for their symptoms. The most common VOM abnormalities were downbeating and gaze-evoked nystagmus and saccadic pursuit. All received immune therapy and most received symptomatic therapy. Most experienced improvement in clinical outcome measures (modified Rankin scale and/or timed 25-foot walk test) or VOM function. By contrast, in the 14 patients in whom VOM dysfunction was nondominant, most had an SPS phenotype and were women. VOM abnormalities, when present, were more subtle, although mostly still consistent with cerebellar and/or brainstem dysfunction.

CONCLUSIONS

Individuals with anti-GAD-associated neurologic disorders may present with prominent VOM abnormalities at the initial symptom onset that localize to the cerebellum and/or brainstem. In our cohort, immune and symptomatic therapies improved clinical outcomes and symptomatology.

Atypical Phenotype in a Spinocerebellar Ataxia Type 2 Kindred

Background

Non-ataxic manifestations in autosomal dominant cerebellar ataxias are variable and influenced by CAG repeat length and age at onset. This report describes a genetically proven SCA2 kindred with an atypical phenotype resembling SCA3.

Case Report

The phenotype of five genetically proven patients with SCA2 in this report differed from the typical phenotype owing to persistence of reflexes late into the course of illness, absence of peripheral neuropathy, and very prominent facial twitches.

Discussion

Despite descriptions of typical phenotypes of SCA, significant variations occur, especially within kindreds. Caution should be exercised in clinical diagnoses of SCA, especially with atypical features.

Serum glutamate decarboxylase antibodies and neurological disorders: when to suspect their association?

OBJECTIVES

To explore different neurological manifestations with suspicion of being associated to serum glutamate decarboxylase antibodies (GAD-Abs) in order to better characterize anti-GAD neurological syndromes.

METHODS

Observational retrospective study including all patients for whom GAD65-Abs titers in serum were requested by the Neurology Department at La Paz University Hospital between 2015 and 2019. GAD-Abs were measured by ELISA. Demographic data, neurological symptoms, comorbidity with diabetes mellitus (DM) or with another autoimmune disease, and GAD-Abs titers were studied. Stiff-person syndrome, ataxia, encephalitis, and epilepsy were considered typical anti-GAD neurological syndromes and were compared to other atypical manifestations.

RESULTS

A total of 173 patients (51.7% men, mean age 51.62) were included. A progressive increase in requests of serum GAD-Abs has occurred over the last 5 years, especially in patients with atypical neurological manifestations. GAD-Abs were found in the serum of 22 patients (12.7%); of those, 15 (68.18%) suffered a typical anti-GAD syndrome. Presence of DM or another organ-specific autoimmune disease was predictive of GAD-AB seropositivity (p < 0.001). 6.6% of requested patients with an atypical syndrome had GAD-Abs, but serum levels were significantly lower than those found in patients with a typical syndrome (706.67 vs 1430.23 UI/mL; Mann-Whitney U, p = 0.034), and were finally diagnosed with another neurological disease.

CONCLUSION

Serum GAD-Abs were infrequently found in patients with clinical phenotypes other than those classically described as anti-GAD disorders, and with very low titers. In typical anti-GAD syndromes, there is a high comorbidity with DM and with other autoimmune diseases, and high serum GAD-Abs levels are usually present.

Deciphering the saccade velocity profile of progressive supranuclear palsy: A sign of latent cerebellar/brainstem dysfunction?

OBJECTIVE

To study whether the velocity profile of horizontal saccades could be used as an indicator of brainstem and cerebellar output dysfunction, depending on progressive supranuclear palsy (PSP) subtype.

METHODS

We compared the velocity profiles in 32 PSP patients of various subtypes with 38 age-matched normal subjects, including Richardson syndrome (RS), PSP-parkinsonism (PSPp), and pure akinesia (PAGF), and cerebellar subtypes of PSP (PSPc).

RESULTS

PSP patients showed reduced peak velocity along with increased duration, especially in the deceleration phase. This alteration was more prominent for larger target eccentricities (20-30 degrees), and correlated with disease severity. The changes were most pronounced in PSPc patients, with irregular increases and decreases in velocity profile, followed by RS patients, whereas the change was smaller in PSPp and normal in PAGF patients.

CONCLUSIONS

Saccade velocity profile can be an indicator of brainstem and/or cerebellar output. Altered velocity profile of PSP patients may reflect the pathology in the brainstem, but may also reflect cerebellar dysfunction, most prominently in PSPc.

SIGNIFICANCE

Saccade velocity profile may be used as an indicator of latent cerebellar/brainstem dysfunction.

The prominent role of the cerebellum in the social learning of the phonological loop in working memory: How language was adaptively built from cerebellar inner speech required during stone-tool making

Based on advances in cerebellum research as to its cognitive, social, and language contributions to working memory, the purpose of this article is to describe new support for the prominent involvement of cerebellar internal models in the adaptive selection of language. Within this context it has been proposed that (1) cerebellar internal models of inner speech during stone-tool making accelerated the adaptive evolution of new cause-and-effect sequences of precision stone-tool knapping requirements, and (2) that these evolving cerebellar internal models coded (i.e., learned in corticonuclear microcomplexes) such cause-and-effect sequences as phonological counterparts and, these, when sent to the cerebral cortex, became new phonological working memory. This article describes newer supportive research findings on (1) the cerebellum's role in silent speech in working memory, and (2) recent findings on genetic aspects (FOXP2) of the role of silent speech in language evolution. It is concluded that within overall cerebro-cerebellar evolution, without the evolution of cerebellar coding of stone-tool making sequences of primitive working memory (beginning approximately 1.7 million years ago) language would not have evolved in the subsequent evolution of Homo sapiens.

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.

An Algorithm for the Diagnosis of Vestibular, Cerebellar, and Oculomotor Disorders Using a Systematized Clinical Bedside Examination

The bedside examination associated with their clinical history remains the most critical means to accurately diagnose the cause for most of the signs and symptoms related to pathology of the cerebellum and vestibular system in patients presenting with dizziness and imbalance. This paper focuses on those critical bedside examinations, suggests when laboratory testing might be useful to confirm the clinical suspicion, and considers the shared neural circuitry within the visual and vestibular systems to offer an algorithmic approach in conducting the clinical bedside examination.

Molecular Mechanisms and Therapeutics for Spinocerebellar Ataxia Type 2

The effective therapeutic treatment and the disease-modifying therapy for spinocerebellar ataxia type 2 (SCA2) (a progressive hereditary disease caused by an expansion of polyglutamine in the ataxin-2 protein) is not available yet. At present, only symptomatic treatment and methods of palliative care are prescribed to the patients. Many attempts were made to study the physiological, molecular, and biochemical changes in SCA2 patients and in a variety of the model systems to find new therapeutic targets for SCA2 treatment. A better understanding of the uncovered molecular mechanisms of the disease allowed the scientific community to develop strategies of potential therapy and helped to create some promising therapeutic approaches for SCA2 treatment. Recent progress in this field will be discussed in this review article.