From normal gait to loss of ambulation in 6 months: a novel presentation of SCA17

Molecular Mechanisms of Spinocerebellar Ataxia Type 17

Spinocerebellar ataxia type 17 (SCA17) is a hereditary neurodegenerative disorder characterized by progressive motor and cognitive decline, leading to severe disability and death. SCA17 is caused by a CAG repeat expansion mutation in the TBP gene, resulting in the production of an abnormally long polyglutamine tract, which classifies it as a polyglutamine disorder. At present, there is no effective treatment for SCA17, and existing therapies provide only symptomatic relief. While the exact pathogenic mechanisms of SCA17 remain unclear, the TBP mutation affects a well-characterized transcription factor, making it an ideal model for studying polyglutamine-related neurodegeneration. Here, we review the clinical features of SCA17 and explore proposed mechanisms of its pathogenesis.

ERK activation precedes Purkinje cell loss in mice with Spinocerebellar ataxia type 17

Spinocerebellar ataxia type 17 (SCA17) is an autosomal dominant neurodegenerative disease caused by CAG expansion in the gene encoding the TATA-binding protein (TBP). The neurological features of SCA17 are Purkinje cell loss and gliosis. We have generated SCA17 transgenic mice which recapitulate the patients' phenotypes and are suitable for the study of the SCA17 pathomechanism. Our previous study identified the activation of mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) occurred in the SCA17 cerebella, this study aims to study the role of ERK activation in SCA17. The levels of pERK, calbindin, and gliosis markers on the mouse cerebellum at 4-8 weeks old were analyzed to elucidate the correlation among behavioral performance, ERK activation and Purkinje cell degeneration. The motor incoordination was initiated in SCA17 mice at 6 weeks old. We found that the presence of TBP nuclear aggregation and microglia activation were observed at 4 weeks old. Gliosis of astrocytes and Bergmann glia, pERK, Bax/Bcl2 ratio, and caspase-3 were significantly increased in the 6-week-old SCA17 mouse cerebellum. In addition to the polyglutamine-protein aggregation in Purkinje cells caused apoptosis cell-autonomously, a significant body of evidence have shown that ERK pathways involves in neuronal apoptosis. Our study showed that the activation of ERK in the astrocytes and Bergmann glia was identified as preceding motor deficits, which suggest the elevated gliosis by ERK activation may contribute to neuronal apoptosis in SCA17 mice.

Huntington's Disease, Huntington's Disease Look-Alikes‎, and Benign Hereditary Chorea: What's New?

Background

The differential diagnosis of chorea syndromes is complex. It includes inherited forms, the most common of which is autosomal dominant Huntington's disease (HD). In addition, there are disorders mimicking HD, the so-called HD-like (HDL) syndromes.

Methods and Results

Here we review main clinical, genetic, and pathophysiological characteristics of HD and the rare HD phenocopies in order to familiarize clinicians with them. Molecular studies have shown that HD phenocopies account for about 1% of suspected HD cases, most commonly due to mutations in C9orf72 (also the main cause of frontotemporal dementia and amyotrophic lateral sclerosis syndromes), TATA box-binding protein (spinocerebellar ataxia type 17 [SCA17]/HDL4), and JPH3 (HDL2). Systematic screening studies also revealed mutations in PRNP (prion disease), VPS13A (chorea-acanthocytosis), ATXN8OS-ATXN8 (SCA8), and FXN (late-onset Friedreich's Ataxia) in single cases. Further differential diagnoses to consider in patients presenting with a clinical diagnosis consistent with HD, but without the HD expansion, include dentatorubral-pallidoluysian atrophy and benign hereditary chorea (TITF1), as well as the recently described form of ADCY5-associated neurodegeneration. Lastly, biallelic mutations in RNF216 and FRRS1L have recently been reported as autosomal recessive phenocopies of HD.

Conclusion

There is a growing list of genes associated with chorea, yet a substantial percentage of patients remain undiagnosed. It is likely that more genes will be discovered in the future and that the clinical spectrum of the described disorders will broaden.