Spinocerebellar ataxia 8: variable phenotype and unique pathogenesis

Migraine With Aura Accompanied by Myoclonus: A Case Report

Migraine is a condition characterized by pulsating headaches, often accompanied by photophobia, phonophobia, and/or gastrointestinal symptoms such as nausea and vomiting. Approximately 15% to one-third of migraine patients experience an aura either before or during the headache. To the best of our knowledge, the occurrence of migraine with myoclonus is extremely rare. This report describes a rare case of migraine with aura accompanied by myoclonus. The patient is a 46-year-old man who developed a visual aura followed by vomiting and a throbbing headache on the right side. As the headache intensified, involuntary movements of the left lower extremity appeared. Brain magnetic resonance imaging (MRI) revealed no structural abnormalities or stroke lesions; however, arterial spin labeling MRI showed hypoperfusion in the right cerebral hemisphere. An ophthalmological evaluation was unremarkable. He was diagnosed with migraine with myoclonus, and the intravenous administration of diazepam and sumatriptan resulted in the cessation of the myoclonus and mild relief of the headache. By the day after admission, the myoclonus and visual symptoms had completely disappeared. The headache resolved by the third day of admission.

Tremor-associated short tandem repeat intermediate and pathogenic expansions in familial essential tremor

There is an obvious clinical-pathological overlap between essential tremor and some known tremor-associated short tandem repeat expansion disorders. The aim is to analyse whether these short tandem repeat genes, including ATXN1, ATXN2, ATXN3, CACNA1A, ATXN7, ATXN8OS, ATXN10, PPP2R2B, TBP, BEAN1, NOP56, DAB1, ATN1, SADM12 and FMR1, are associated with familial essential tremor patients. Genetic analysis of repeat sizes in tremor-associated short tandem repeat expansions was performed in a large cohort of 515 familial essential tremor probands and 300 controls. The demographic and clinical features among carriers of pathogenic expansions, intermediate repeats and non-carriers were compared. A total of 18 out of 515 (18/515, 3.7%) patients were found to have repeats expansions, including 12 cases (12/515, 2.5%) with intermediate repeat expansions (one ATXN1, eight TBP, two FMR1, one ATN1), and six cases (6/515, 1.2%) with pathogenic expansions (one ATXN1, one ATXN2, one ATXN8OS, one PPP2R2B, one FMR1, one SAMD12). There were no statistically significant differences in intermediate repeats compared to healthy controls. Furthermore, there were no significant differences in demographics and clinical features among individuals with pathogenic expansions, intermediate repeat expansions carriers and non-carriers. Our study indicates that the intermediate repeat expansion in tremor-associated short tandem repeat expansions does not pose an increased risk for essential tremor, and rare pathogenic expansion carriers have been found in the familial essential tremor cohort. The diagnosis of essential tremor based solely on clinical symptoms remains a challenge in distinguishing it from known short tandem repeat expansions diseases with overlapping clinical-pathological features.

Tremor in Spinocerebellar Ataxia: A Scoping Review

Background

Spinocerebellar ataxia (SCA) denotes an expanding list of autosomal dominant cerebellar ataxias. Although tremor is an important aspect of the clinical spectrum of the SCAs, its prevalence, phenomenology, and pathophysiology are unknown.

Objectives

This review aims to describe the various types of tremors seen in the different SCAs, with a discussion on the pathophysiology of the tremors, and the possible treatment modalities.

Methods

The authors conducted a literature search on PubMed using search terms including tremor and the various SCAs. Relevant articles were included in the review after excluding duplicate publications.

Results

While action (postural and intention) tremors are most frequently associated with SCA, rest and other rare tremors have also been documented. The prevalence and types of tremors vary among the different SCAs. SCA12, common in certain ethnic populations, presents a unique situation, where the tremor is typically the principal manifestation. Clinical manifestations of SCAs may be confused with essential tremor or Parkinson's disease. The pathophysiology of tremors in SCAs predominantly involves the cerebellum and its networks, especially the cerebello-thalamo-cortical circuit. Additionally, connections with the basal ganglia, and striatal dopaminergic dysfunction may have a role. Medical management of tremor is usually guided by the phenomenology and associated clinical features. Deep brain stimulation surgery may be helpful in treatment-resistant tremors.

Conclusions

Tremor is an elemental component of SCAs, with diverse phenomenology, and emphasizes the role of the cerebellum in tremor. Further studies will be useful to delineate the clinical, pathophysiological, and therapeutic aspects of tremor in SCAs.

Neuropathology of spinocerebellar ataxia type 8: Common features and unique tauopathy

Spinocerebellar ataxia type 8 (SCA8) is a neurodegenerative condition that presents with several neurological symptoms, such as cerebellar ataxia, parkinsonism, and cognitive impairment. It is caused by a CTA/CTG repeat expansion on chromosome 13q21 (ataxin 8 opposite strand [ATXN8OS]). However, the pathological significance of this expansion remains unclear. Moreover, abnormal CTA/CTG repeat expansions in ATXN8OS have also been reported in other neurodegenerative diseases, including progressive supranuclear palsy. In this study, we analyzed all available autopsy cases in Japan to investigate common pathological features and profiles of tau pathology in each case. Severe neuronal loss in the substantia nigra and prominent loss of Purkinje cells, atrophy of the molecular layer, and proliferation of Bergmann glia in the cerebellum were common features. Regarding tauopathy, one case presented with progressive supranuclear palsy-like 4-repeat tauopathy in addition to mild Alzheimer-type 3- and 4-repeat tauopathy. Another case showed 3- and 4-repeat tauopathy accentuated in the brainstem. The other two cases lacked tauopathy after extensive immunohistochemical studies. The present study confirmed common pathological features of SCA8 as degeneration of the substantia nigra in addition to the cerebellum. Our study also confirmed unique tauopathy in two of four cases, indicating the necessity to further collect autopsy cases.

Coexistence of multiple sclerosis and spinocerebellar ataxia type-8

Cerebellar dysfunction is likely to cause severe and treatment-resistant disability in multiple sclerosis (MS). Certain spinocerebellar ataxia (SCA)-related alleles can increase MS susceptibility, and channel polymorphisms can impact disability measures. Following an index patient with the coexistence of MS and SCA Type-8 (SCA8) in the MS clinic, an institutional engine search for MS and hereditary ataxia coexistence was conducted but did not reveal any other cases. This extremely rare coexistence of MS and SCA8 in our index patient may be incidental; however, a yet-to-be-identified contribution of coexistent hereditary ataxia(s) to the susceptibility of a prominent progressive ataxia MS phenotype cannot be ruled out.

Review of Hereditary and Acquired Rare Choreas

Background:

Movement disorders are often a prominent part of the phenotype of many neurologic rare diseases. In order to promote awareness and diagnosis of these rare diseases, the International Parkinson’s and Movement Disorders Society Rare Movement Disorders Study Group provides updates on rare movement disorders.

Methods:

In this narrative review, we discuss the differential diagnosis of the rare disorders that can cause chorea.

Results:

Although the most common causes of chorea are hereditary, it is critical to identify acquired or symptomatic choreas since these are potentially treatable conditions. Disorders of metabolism and mitochondrial cytopathies can also be associated with chorea.

Discussion:

The present review discusses clues to the diagnosis of chorea of various etiologies. Authors propose algorithms to help the clinician in the diagnosis of these rare disorders.

The First Case of Spinocerebellar Ataxia Type 8 in Monozygotic Twins

Spinocerebellar ataxia type 8 (SCA8) is a rare hereditary cerebellar ataxia showing mainly pure cerebellar ataxia. We herein report cases of SCA8 in Japanese monozygotic twins that presented with nystagmus, dysarthria, and limb and truncal ataxia. Their ATXN8OS CTA/CTG repeats were 25/97. They showed similar manifestations, clinical courses, and cerebellar atrophy on magnetic resonance imaging. Some of their pedigrees had nystagmus but not ataxia. These are the first monozygotic twins with SCA8 to be reported anywhere in the world. Although not all subjects with the ATXN8OS CTG expansion develop cerebellar ataxia, these cases suggest the pathogenesis of ATXN8OS repeat expansions in hereditary cerebellar ataxia.

Disrupted Calcium Signaling in Animal Models of Human Spinocerebellar Ataxia (SCA)

Spinocerebellar ataxias (SCAs) constitute a heterogeneous group of more than 40 autosomal-dominant genetic and neurodegenerative diseases characterized by loss of balance and motor coordination due to dysfunction of the cerebellum and its efferent connections. Despite a well-described clinical and pathological phenotype, the molecular and cellular events that underlie neurodegeneration are still poorly undaerstood. Emerging research suggests that mutations in SCA genes cause disruptions in multiple cellular pathways but the characteristic SCA pathogenesis does not begin until calcium signaling pathways are disrupted in cerebellar Purkinje cells. Ca²⁺ signaling in Purkinje cells is important for normal cellular function as these neurons express a variety of Ca²⁺ channels, Ca²⁺-dependent kinases and phosphatases, and Ca²⁺-binding proteins to tightly maintain Ca²⁺ homeostasis and regulate physiological Ca²⁺-dependent processes. Abnormal Ca²⁺ levels can activate toxic cascades leading to characteristic death of Purkinje cells, cerebellar atrophy, and ataxia that occur in many SCAs. The output of the cerebellar cortex is conveyed to the deep cerebellar nuclei (DCN) by Purkinje cells via inhibitory signals; thus, Purkinje cell dysfunction or degeneration would partially or completely impair the cerebellar output in SCAs. In the absence of the inhibitory signal emanating from Purkinje cells, DCN will become more excitable, thereby affecting the motor areas receiving DCN input and resulting in uncoordinated movements. An outstanding advantage in studying the pathogenesis of SCAs is represented by the availability of a large number of animal models which mimic the phenotype observed in humans. By mainly focusing on mouse models displaying mutations or deletions in genes which encode for Ca²⁺ signaling-related proteins, in this review we will discuss the several pathogenic mechanisms related to deranged Ca²⁺ homeostasis that leads to significant Purkinje cell degeneration and dysfunction.

Epilepsy in spinocerebellar ataxia type 8: a case report

Background

Spinocerebellar ataxia type 8 is an uncommon genetic condition and presents with gait disturbances, ataxia, dysarthria, nystagmus, and cognitive and psychiatric abnormalities. Seizures are extremely uncommon in the spinocerebellar ataxias and have been reported only once before in a patient with spinocerebellar ataxia type 8. This case report highlights the need to evaluate spells in patients with a known neurodegenerative or genetic disease to exclude seizures, and it stresses the importance of timely diagnosis and therapy.

Case presentation

The patient was a 22-year-old Caucasian woman with known spinocerebellar ataxia 8 since age 10 years. She was admitted to our hospital with new-onset left hemiparesis and encephalopathy in addition to chronic occurrence of multiple spells of confusion and oromanual automatisms with postictal lethargy. Testing confirmed that she was having recurrent seizures with episodes of nonconvulsive status epilepticus. Urgent treatment with antiepileptic therapy was initiated; her seizures resolved shortly thereafter, and her mental status improved. Her left hemiparesis has improved; she remains seizure-free; and she has returned to her baseline antiepileptic medications following physical therapy.

Conclusions

Seizures have been reported extremely rarely in association with spinocerebellar ataxia 8, but they must be considered in the differential diagnosis of patients with spells of altered awareness, especially in those with a known neurodegenerative or genetic condition. Clinicoradiological correlation with symptoms can help expedite diagnosis and treatment. Expert consultation with epileptologists at the earliest signs can help establish the diagnosis quickly, minimize morbidity, and enhance recovery.

SCA8 RAN polySer protein preferentially accumulates in white matter regions and is regulated by eIF3F

Spinocerebellar ataxia type 8 (SCA8) is caused by a bidirectionally transcribed CTG·CAG expansion that results in the in vivo accumulation of CUG RNA foci, an ATG-initiated polyGln and a polyAla protein expressed by repeat-associated non-ATG (RAN) translation. Although RAN proteins have been reported in a growing number of diseases, the mechanisms and role of RAN translation in disease are poorly understood. We report a novel toxic SCA8 polySer protein which accumulates in white matter (WM) regions as aggregates that increase with age and disease severity. WM regions with polySer aggregates show demyelination and axonal degeneration in SCA8 human and mouse brains. Additionally, knockdown of the eukaryotic translation initiation factor eIF3F in cells reduces steady-state levels of SCA8 polySer and other RAN proteins. Taken together, these data show polySer and WM abnormalities contribute to SCA8 and identify eIF3F as a novel modulator of RAN protein accumulation.

RNA toxicity and foci formation in microsatellite expansion diseases

More than 30 incurable neurological and neuromuscular diseases are caused by simple microsatellite expansions consisted of 3-6 nucleotides. These repeats can occur in non-coding regions and often result in a dominantly inherited disease phenotype that is characteristic of a toxic RNA gain-of-function. The expanded RNA adopts unusual secondary structures, sequesters various RNA binding proteins to form insoluble nuclear foci, and causes cellular defects at a multisystem level. Nuclear foci are dynamic in size, shape and colocalization of RNA binding proteins in different expansion diseases and tissue types. This review sets to provide new insights into the disease mechanisms of RNA toxicity and foci modulation, in light of recent advancement on bi-directional transcription, antisense RNA, repeat-associated non-ATG translation and beyond.

Bolivian kindred with combined spinocerebellar ataxia types 2 and 10

BACKGROUND

Spinocerebellar ataxias (SCA) are a group of rare hereditary neurodegenerative disorders. Rare cases of two SCA mutations in the same individual have been reported in the literature, however, family descriptions are lacking.

AIMS

To characterize a family with combined SCA2 and SCA10 mutations.

MATERIALS & METHODS

Analysis of the clinical features and genetic findings of a Bolivian family expressing both SCA2 and SCA10 mutations.

RESULTS

The index case and his mother had both SCA2 and SCA10 mutations with a combined clinical phenotype of both disorders, including slow saccades (SCA2) and seizures (SCA10). The uncle of the index case had only an SCA10 mutation.

DISCUSSION

Although the presence of two SCA mutations in the same individuals may be coincidental, the low probability of having both mutations suggests that these mutations might be particularly prevalent in Bolivian population.

CONCLUSION

This is the first description of a family with two SCA mutations with affected subjects having a combined SCA2 and SCA10 phenotype.

Non-Ataxic Phenotypes of SCA8 Mimicking Amyotrophic Lateral Sclerosis and Parkinson Disease

Background

Spinocerebellar ataxia (SCA) type 8 (SCA8) is an inherited neurodegenerative disorder caused by the expansion of untranslated CTA/CTG triplet repeats on 13q21. The phenomenology of SCA8 is relatively varied when compared to the other types of SCAs and its spectrum is not well established.

Case Report

Two newly detected cases of SCA8 with the nonataxic phenotype and unusual clinical manifestations such as dopaminergic-treatment-responsive parkinsonism and amyotrophic lateral sclerosis (ALS) are described herein. Family A expressed good dopaminergic treatment-responsive parkinsonism as an initial manifestation and developed mild cerebellar ataxia with additional movements, including dystonic gait and unusual oscillatory movement of the trunk, during the disease course. The proband of family B presented as probable ALS with cerebellar atrophy on brain MRI, with a positive family history (a brother with typical cerebellar ataxia) and genetic confirmation for SCA8.

Conclusions

Our findings support that the non-ataxic phenotypes could be caused by a mutation of the SCA8 locus which might affect neurons other than the cerebellum.

Novel neuronal cytoplasmic inclusions in a patient carrying SCA8 expansion mutation

It has been reported that abnormal processing of pre-mRNA is caused by abnormal triplet expansion. Non-coding triplet expansions produce toxic RNA to alter RNA splicing activities. However, there has been no report on the globular RNA aggregation in neuronal cytoplasmic inclusions (NCIs) up to now. We herein report on an autopsy case (genetically determined as spinocerebellar atrophy 8 (SCA8)) with hitherto undescribed NCIs throughout the brain. NCIs were chiefly composed of small granular particles, virtually identical to ribosomes. Neurological features are comparable to the widespread lesions of the brain, including the spinal cord. Although 1C2-positivity of NCIs might be induced by reverse transcription of the CTG expansion, it remains to be clarified how abnormal aggregations of ribosome and extensive brain degeneration are related to the reverse or forward transcripts of the expanded repeat.

Genetic screening of Greek patients with Huntington’s disease phenocopies identifies an SCA8 expansion

Huntington’s disease (HD) is an autosomal dominant disorder characterized by a triad of chorea, psychiatric disturbance and cognitive decline. Around 1% of patients with HD-like symptoms lack the causative HD expansion and are considered HD phenocopies. Genetic diseases that can present as HD phenocopies include HD-like syndromes such as HDL1, HDL2 and HDL4 (SCA17), some spinocerebellar ataxias (SCAs) and dentatorubral-pallidoluysian atrophy (DRPLA). In this study we screened a cohort of 21 Greek patients with HD phenocopy syndromes formutations causing HDL2, SCA17, SCA1, SCA2, SCA3,SCA8, SCA12 and DRPLA. Fifteen patients (71%) had a positive family history. We identified one patient (4.8% of the total cohort) with an expansion of 81 combined CTA/CTG repeats at the SCA8 locus. This falls within what is believed to be the high-penetrance allele range. In addition to the classic HD triad, the patient had features of dystonia and oculomotor apraxia. There were no cases of HDL2, SCA17, SCA1, SCA2, SCA3, SCA12 or DRPLA. Given the controversy surrounding the SCA8 expansion, the present finding may be incidental. However, if pathogenic, it broadens the phenotype that may be associated with SCA8 expansions. The absence of any other mutations in our cohort is not surprising, given the low probability of reaching a genetic diagnosis in HD phenocopy patients.

Animal models of human cerebellar ataxias: a cornerstone for the therapies of the twenty-first century

Cerebellar ataxias represent a group of disabling neurological disorders. Our understanding of the pathogenesis of cerebellar ataxias is continuously expanding. A considerable number of laboratory animals with neurological mutations have been reported and numerous relevant animal models mimicking the phenotype of cerebellar ataxias are becoming available. These models greatly help dissecting the numerous mechanisms of cerebellar dysfunction, a major step for the assessment of therapeutics targeting a given deleterious pathway and for the screening of old or newly synthesized chemical compounds. Nevertheless, differences between animal models and human disorders should not be overlooked and difficulties in terms of characterization should not be occulted. The identification of the mutations of many hereditary ataxias, the development of valuable animal models, and the recent identifications of the molecular mechanisms underlying cerebellar disorders represent a combination of key factors for the development of anti-ataxic innovative therapies. It is anticipated that the twenty-first century will be the century of effective therapies in the field of cerebellar ataxias. The animal models are a cornerstone to reach this goal.