Autosomal Dominant Spinocerebellar Ataxias: An Asian Perspective

Efficacy and Safety of Taltirelin Hydrate in Patients With Ataxia Due to Spinocerebellar Degeneration

OBJECTIVE

We conducted this study to assess the efficacy and safety of taltirelin hydrate (TH) in patients with ataxia due to spinocerebellar degeneration (SCD).

METHODS

Patients were randomly assigned to either the taltirelin group (5 mg orally, twice daily) or the control group. The primary endpoint was the change in the Korean version of the Scale for the Assessment and Rating of Ataxia (K-SARA) score at 24 weeks. The secondary endpoints included changes in the K-SARA score at 4 and 12 weeks as well as the Clinical Global Impression Scale, the five-level version of the EuroQol five-dimensional questionnaire, the Tinetti balance test, and gait analysis at 4, 12, and 24 weeks.

RESULTS

A total of 149 patients (hereditary:nonhereditary=86:63) were enrolled. There were significant differences in the change in the K-SARA score at 24 weeks from baseline between the taltirelin group and the control group (-0.51±2.79 versus 0.36±2.62, respectively; p=0.0321). For the K-SARA items, the taltirelin group had significantly lower "Stance" and "Speech disturbance" subscores than the control group (-0.04±0.89 versus 0.23±0.79 and -0.07±0.74 versus 0.18±0.67; p=0.0270 and 0.0130, respectively). However, there were no significant differences in changes in other secondary efficacy outcome measures at 24 weeks from baseline between the two treatment arms (p>0.05).

CONCLUSION

Clinicians might consider the use of TH in the treatment of patients with ataxia due to SCD.

NOTCH2NLC GGC intermediate repeat with serine induces hypermyelination and early Parkinson's disease-like phenotypes in mice

BACKGROUND

The expansion of GGC repeats (typically exceeding 60 repeats) in the 5' untranslated region (UTR) of the NOTCH2NLC gene (N2C) is linked to N2C-related repeat expansion disorders (NREDs), such as neuronal intranuclear inclusion disease (NIID), frontotemporal dementia (FTD), essential tremor (ET), and Parkinson's disease (PD). These disorders share common clinical manifestations, including parkinsonism, dementia, seizures, and muscle weakness. Intermediate repeat sizes ranging from 40 to 60 GGC repeats, particularly those with AGC-encoded serine insertions, have been reported to be associated with PD; however, the functional implications of these intermediate repeats with serine insertion remain unexplored.

METHODS

Here, we utilized cellular models harbouring different sizes of N2C variant 2 (N2C2) GGC repeat expansion and CRISPR-Cas9 engineered transgenic mouse models carrying N2C2 GGC intermediate repeats with and without serine insertion to elucidate the underlying pathophysiology associated with N2C intermediate repeat with serine insertion in NREDs.

RESULTS

Our findings revealed that the N2C2 GGC intermediate repeat with serine insertion (32G13S) led to mitochondrial dysfunction and cell death in vitro. The neurotoxicity was influenced by the length of the repeat and was exacerbated by the presence of the serine insertion. In 12-month-old transgenic mice, 32G13S intensified intranuclear aggregation and exhibited early PD-like characteristics, including the formation of α-synuclein fibers in the midbrain and the loss of tyrosine hydroxylase (TH)-positive neurons in both the cortex and striatum. Additionally, 32G13S induced neuronal hyperexcitability and caused locomotor behavioural impairments. Transcriptomic analysis of the mouse cortex indicated dysregulation in calcium signaling and MAPK signaling pathways, both of which are critical for mitochondrial function. Notably, genes associated with myelin sheath components, including MBP and MOG, were dysregulated in the 32G13S mouse. Further investigations using immunostaining and transmission electron microscopy revealed that the N2C intermediate repeat with serine induced mitochondrial dysfunction-related hypermyelination in the cortex.

CONCLUSIONS

Our in vitro and in vivo investigations provide the first evidence that the N2C-GGC intermediate repeat with serine promotes intranuclear aggregation of N2C, leading to mitochondrial dysfunction-associated hypermyelination and neuronal hyperexcitability. These changes contribute to motor deficits in early PD-like neurodegeneration in NREDs.

Repeat expansions in NOP56 are a cause of spinocerebellar ataxia Type 36 in the British population

Spinocerebellar ataxias form a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by progressive cerebellar ataxia. Their prevalence varies among populations and ethnicities. Spinocerebellar ataxia 36 is caused by a GGCCTG repeat expansion in the first intron of the NOP56 gene and is characterized by late-onset ataxia, sensorineural hearing loss and upper and lower motor neuron signs, including tongue fasciculations. Spinocerebellar ataxia 36 has been described mainly in East Asian and Western European patients and was thought to be absent in the British population. Leveraging novel bioinformatic tools to detect repeat expansions from whole-genome sequencing, we analyse the NOP56 repeat in 1257 British patients with hereditary ataxia and in 7506 unrelated controls. We identify pathogenic repeat expansions in five families (seven patients), representing the first cohort of White British descent patients with spinocerebellar ataxia 36. Employing in silico approaches using whole-genome sequencing data, we found an 87 kb shared haplotype in among the affected individuals from five families around the NOP56 repeat region, although this block was also shared between several controls, suggesting that the repeat arises on a permissive haplotype. Clinically, the patients presented with slowly progressive cerebellar ataxia with a low rate of hearing loss and variable rates of motor neuron impairment. Our findings show that the NOP56 expansion causes ataxia in the British population and that spinocerebellar ataxia 36 can be suspected in patients with a late-onset, slowly progressive ataxia, even without the findings of hearing loss and tongue fasciculation.

Spinocerebellar ataxia type 40: A case report and literature review

Spinocerebellar ataxias (SCAs) are a group of neurodegenerative diseases with ataxia as the main clinical manifestation. The phenotypes, gene mutations, and involved sites of different subtypes show a high degree of heterogeneity. The incidence of SCA varies greatly among different subtypes and the case of SCA40 is extremely rare. The aim of this study is to report a rare case of SCA40 and systematically review the incidence, gene mutation, and phenotype of SCAs, especially SCA40.

Genetic testing for clinically suspected spinocerebellar ataxias: report from a tertiary referral centre in India

Spinocerebellar ataxias (SCAs) are a heterogeneous group of neurodegenerative syndromes, characterized by a wide range of muscular weakness and motor deficits, caused due to cerebellar degeneration. The prevalence of the syndromes of SCA varies across the world and is known to be linked to the instability of trinucleotide repeats within the high-end normal alleles, along with susceptible haplotype. We estimated sizes of the CAG or GAA repeat expansions at the SCA1, SCA2, SCA3, SCA12 and frataxin loci among 864 referrals of subjects to genetic counselling and testing (GCAT) clinic, National Institute of Mental Health and Neurosciences, Bengaluru, India, with suspected SCA. The most frequent mutations detected were SCA1 (n = 100 (11.6%)) and SCA2 (n = 98 (11.3%)) followed by SCA3 (n = 40 (4.6%)), FRDA (n = 20 (2.3%)) and SCA12 (n = 8 (0.9%)).

Molecular diagnosis of neurogenetic disorders involving trinucleotide repeat expansions

There are more than 15 known neurogenetic disorders involving trinucleotide repeat expansion. Expanded repeats range from small expansions of 20-100 copies to larger expansions of up to several thousand units. These dynamic expansions result in variability in age of onset, degree of severity and clinical presentation. Individuals carrying alleles in the intermediate range, known as premutation alleles, are often asymptomatic, but can potentially transmit a further expanded allele to his/her offspring. For autosomal dominant adult-onset disorders, carriers are asymptomatic prior to disease onset. With current molecular tools, it is now possible to determine the presence and number of expanded repeats for accurate diagnosis, presymptomatic testing and carrier status screening. This review examines some of the current approaches for molecular diagnosis and discusses the issues unique to triplet repeat diseases.

Seminar on choreas

Chorea is one of the major types of involuntary movement disorders originating from dysfunctional neuronal networks interconnecting the basal ganglia and frontal cortical motor areas. The syndrome is characterised by a continuous flow of random, brief, involuntary muscle contractions and can result from a wide variety of causes. Diagnostic work-up can be straightforward in patients with a positive family history of Huntington's disease or acute-onset hemichorea in patients with lacunar stroke, but it can be a challenging and complex task in rare autoimmune or genetic choreas. Principles of management focus on establishing an aetiological classification and, if possible, removal of the cause. Preventive strategies may be possible in Huntington's disease where genetic counselling plays a major part. In this review we summarise the current understanding of the neuroanatomy and pathophysiology of chorea, its major aetiological classes, and principles of diagnostic work-up and management.

Genetic analysis of SCA2, 3 and 17 in idiopathic Parkinson's disease

Recent reports of SCA2 and SCA3 patients who presented with levodopa responsive parkinsonism have generated considerable interest as they have implications for genetic testing. It is unclear whether ethnic race alone or founder effects within certain geographical region explain such an association. In this study, we conducted genetic analysis of SCA2, 3, 17 in an ethnic Chinese cohort with early onset and familial Parkinson's disease (PD) and healthy controls. A total of 191 subjects comprising of 91 PD and 100 healthy controls were examined. We identified one positive case of SCA2 in an early-onset sporadic PD patient who had CAG 36 repeats, yielding a prevalence of 2.2% in early-onset sporadic PD patients and less than 1.0% in our study PD population. The size of the repeats was lower than the expanded repeats (38-57) in SCA2 patients with ataxia in our population. All the children of the patient were physically normal even though some of them carried the repeat expansion of similar size. No cases and controls were positive for SCA3 and SCA17. We do not think routine screening of SCA2, SCA3 and SCA17 for all idiopathic PD patients is cost-effective in our ethnic Chinese population. However, SCA2 should be a differential diagnosis in young onset sporadic PD when genetic mutations of other known PD genes have been excluded.

Rare genetically defined causes of dementia

Several genetic disorders, though rare, are associated or present with dementia. Developments in the field of genetics are contributing to clarify and expand our knowledge of the complex physiopathological mechanisms leading to neurodegeneration and cognitive decline. Disorders associated with misfolded and aggregated proteins and lipid, metal or energy metabolism are examples of the multifarious disease processes converging in the clinical features of dementia, either as its predominant feature, as in cases of Alzheimer's disease (AD) or frontotemporal dementia (FTD), or as part of a cohort of accompanying or late-developing symptoms, as in Parkinson's disease (PD) or amyotrophic lateral sclerosis with dementia (ALS-D). Awareness of these disorders, allied with recent advances in genetic, biochemical and neuroimaging techniques, may lead to early diagnosis, successful treatment and better prognosis.