Severity and Progression Rate of Cerebellar Ataxia in 16q-linked Autosomal Dominant Cerebellar Ataxia (16q-ADCA) in the Endemic Nagano Area of Japan

Spinocerebellar ataxia type 31: A clinical and radiological literature review

Spinocerebellar ataxia type 31 (SCA31) is an autosomal dominant disease, classified amongst pure cerebellar ataxias (ADCA type 3). While SCA31 is the third most prevalent autosomal dominant ataxia in Japan, it is extremely rare in other countries. A literature review was conducted on PubMed, where we included all case reports and studies describing the clinical presentation of original SCA31 cases. The clinical and radiological features of 374 patients issued from 25 studies were collected. This review revealed that the average age of onset was 59.1 ± 3.3 years, with symptoms of slowly progressing ataxia and dysarthria. Other common clinical features were oculomotor dysfunction (38.8%), dysphagia (22.1%), hypoacousia (23.3%), vibratory hypoesthesia (24.3%), and dysreflexia (41.6%). Unfrequently, abnormal movements (7.4%), extrapyramidal symptoms (4.5%) and cognitive impairment (6.9%) may be observed. Upon radiological examination, clinicians can expect a high prevalence of cerebellar atrophy (78.7%), occasionally accompanied by brainstem (9.1%) and cortical (9.1%) atrophy. Although SCA31 is described as a slowly progressive pure cerebellar syndrome characterized by cerebellar signs such as ataxia, dysarthria and oculomotor dysfunction, this study evaluated a high prevalence of extracerebellar manifestations. Extracerebellar signs were observed in 52.5% of patients, primarily consisting of dysreflexia, vibratory hypoesthesia and hypoacousia. Nonetheless, we must consider the old age and longstanding disease course of patients as a confounding factor for extracerebellar sign development, as some may not be directly attributable to SCA31. Clinicians should consider SCA31 in patients with a hereditary, pure cerebellar syndrome and in patients with extracerebellar signs.

Insight Into Spinocerebellar Ataxia Type 31 (SCA31) From Drosophila Model

Spinocerebellar ataxia type 31 (SCA31) is a progressive neurodegenerative disease characterized by degeneration of Purkinje cells in the cerebellum. Its genetic cause is a 2.5- to 3.8-kb-long complex pentanucleotide repeat insertion containing (TGGAA)n, (TAGAA)n, (TAAAA)n, and (TAAAATAGAA)n located in an intron shared by two different genes: brain expressed associated with NEDD4-1 (BEAN1) and thymidine kinase 2 (TK2). Among these repeat sequences, (TGGAA)n repeat was the only sequence segregating with SCA31, which strongly suggests its pathogenicity. In SCA31 patient brains, the mutant BEAN1 transcript containing expanded UGGAA repeats (UGGAA_exp) was found to form abnormal RNA structures called RNA foci in cerebellar Purkinje cell nuclei. In addition, the deposition of pentapeptide repeat (PPR) proteins, poly(Trp-Asn-Gly-Met-Glu), translated from UGGAA_exp RNA, was detected in the cytoplasm of Purkinje cells. To uncover the pathogenesis of UGGAA_exp in SCA31, we generated Drosophila models of SCA31 expressing UGGAA_exp RNA. The toxicity of UGGAA_exp depended on its length and expression level, which was accompanied by the accumulation of RNA foci and translation of repeat-associated PPR proteins in Drosophila, consistent with the observation in SCA31 patient brains. We also revealed that TDP-43, FUS, and hnRNPA2B1, motor neuron disease–linked RNA-binding proteins bound to UGGAA_exp RNA, act as RNA chaperones to regulate the formation of RNA foci and repeat-associated translation. Further research on the role of RNA-binding proteins as RNA chaperones may also provide a novel therapeutic strategy for other microsatellite repeat expansion diseases besides SCA31.

Test-retest reliability and minimal detectable change of the Balance Evaluation Systems Test and its two abbreviated versions in persons with mild to moderate spinocerebellar ataxia: A pilot study

BACKGROUND:

The reliability of the evaluation of the Balance Evaluation Systems Test (BESTest) and its two abbreviated versions are confirmed for balance characteristics and reliability. However, they are not utilized in cases of spinocerebellar ataxia (SCA).

OBJECTIVE:

We aimed to examine the test-retest reliability and minimal detectable change (MDC) of the BESTest and its abbreviated versions in persons with mild to moderate spinocerebellar ataxia.

METHODS:

The BESTest was performed in 20 persons with SCA at baseline and one month later. The scores of the abbreviated version of the BESTest were determined from the BESTest scores. The interclass correlation coefficient (1,1) was used as a measure of relative reliability. Furthermore, we calculated the MDC in the BESTest and its abbreviated versions.

RESULTS:

The intraclass correlation coefficients (1,1) and MDC at 95% confidence intervals were 0.92, 8.7(8.1%), 0.91, 4.1(14.5%), and 0.81, 5.2(21.6%) for the Balance, Mini-Balance, and Brief-Balance Evaluation Systems Tests, respectively.

CONCLUSIONS:

The BESTest and its abbreviated versions had high test-retest reliability. The MDC values of the BESTest could enable clinicians and researchers to interpret changes in the balance of patients with SCA more precisely.

Evaluation of walking smoothness using wearable robotic system curara® for spinocerebellar degeneration patients

This paper aimed to verify the effectiveness of the wearable robotic system "curara" for patients with spinocerebellar degeneration (SCD) by evaluating walking smoothness. The curara system supports the wearer's gait using a synchronization control method that uses a neural oscillator based on a central pattern generator network. The system reflects the motional intention by adjusting the synchronization gains. This modifies the degree of interactive coordinated motion between the curara and the wearer. As a feasibility study, we evaluated the waking smoothness of 10 patients with SCD using three gain condition settings. Harmonic ratio (HR), which has been used extensively to quantify the smoothness during walking, was used to assess their walking. The results show that most HRs in the medio-lateral, anterior-posterior, and vertical directions using the three gain conditions were higher than those for patients not wearing the system. In particular, the increasing rates of the HR in all directions during the gait support were 11.1%, 23.4%, and 23.2% compared with unassisted walking, when the gain condition settings of hip and knee joints are set at 0.4 and 0.5, respectively. Consequently, these results verified the effectiveness of the curara system for patients with SCD.

Inter-generational instability of inserted repeats during transmission in spinocerebellar ataxia type 31

The causative mutation for spinocerebellar ataxia type 31 (SCA31) is an intronic insertion containing pathogenic pentanucleotide repeats, (TGGAA)_n. We examined to what degree the inserted repeats were unstable during transmission. In 14 parent-child pairs, the average change of onset age was -6.4±7.3 years (mean±s.d.) in the child generation when compared with the parent generation. Of the 11 pairs analyzed, six showed expansion of inserted repeat length during transmission, and five showed contraction. On average, the inserted repeats expanded by 12.2±32.7 bp during transmission, but their mean length (with a 95% confidence interval) was not significantly different between parent and child generations. We consider that the length of the inserted repeats in SCA31 is changeable during transmission, but inter-generational instability is not marked, as far as the current sizing method can determine.

Clinical characteristics of combined cases of spinocerebellar ataxia types 6 and 31

This study reports the first family in which spinocerebellar ataxia type 6 (SCA6) and spinocerebellar ataxia type 31 (SCA31) mutations were seen. An index patient first presented to our hospital due to gait and speech disturbances. Subsequent clinical investigation of this patient and her family members revealed consistent pure cerebellar ataxia transmitted in an autosomal-dominant manner. Genetic examination unexpectedly demonstrated that two of the five affected individuals had expansions of SCA6 and SCA31, while two others had SCA31 alone and the remaining had SCA6. Clinical manifestations were more severe in individuals with combined mutations relative to those with single mutation, suggesting that the SCA6 and SCA31 mutations have a cumulative pathogenic effect.

[A case of 77-year-old male with spinocerebellar ataxia type 31 with left dominant dystonia]

We report on the case of a 77-year-old male with genetically proven spinocerebellar ataxia type 31 (SCA31) who had dystonia. He was referred to our hospital for evaluation following a 6-year history of slowly progressive unsteadiness of his left leg during walking and dysarthria at the age of 62 years old. On the basis of his symptoms, we diagnosed him as spinocerebellar degeneration (SCD), and prescribed taltirelin hydrate. However, his symptoms continued to worsen. He required a cane for walking at the age of 63 years, and a wheelchair at the age of 66 years. He was admitted to our hospital following acute cerebral infarction at the age of 77 years. On examination at admission, right hemiparesis and cerebellar ataxia were detected. And left hallux moved involuntarily toward the top surface of the foot at rest, that is dystonia. The dystonia was not associated with cerebral infarction, because it had been several years with dystonia that he got cerebral infarction. Genetic analysis revealed that this patient harbored a heterozygous SCA31 mutation. Previously there have been no reports of SCA31 associated with dystonia. Our case report support clinical heterogeneity of SCA31, and highlight the importance of considering this type in patients with dystonia and ataxia. Patients with the combination of dystonia and ataxia and a family history of a neurodegenerative disorder should be tested for SCA31.

[Clinical features and MRI findings in spinocerebellar ataxia type 31 (SCA31) comparing with spinocerebellar ataxia type 6 (SCA6)]

Since the discovery of spinocerebellar ataxia type 31 (SCA31) gene, we identified 6 patients whose SCA type had been unkown for a long period of time as having SCA31 in our hospital and realized that SCA31 is not a rare type of autosomal dominant spinocerebellar ataxia in this region. We examined and compared the clinical details of these six SCA31 patients and the same number of SCA6 patients, finding that some SCA31 patients had hearing loss in common while there are more wide range and complicated signs of extra cerebellum in SCA6 such as pyramidal signs, extrapyramidal signs, dizzy sensations or psychotic, mental problems. There is a significant difference in the number of extracerebellar symptoms between SCA31 and SCA6. There are differences also in MRI findings. Cerebellar atrophy starts from the upper vermis in SCA31, as well as some SCA types, whereas the 4th ventricule becomes enlarged in SCA6 even in the early stage of disease. We suggest that these differences in clinical and MRI findings can be clues for accurate diagnosis before gene analysis.

Comparisons of acoustic function in SCA31 and other forms of ataxias

OBJECTIVE

To investigate whether acoustic impairment can be one of the characteristic extracerebellar symptoms in sporadic and hereditary ataxias including spinocerebellar ataxia type 31 (SCA31).

METHODS

We investigated genotypes of dominant ataxia families, and determined a frequency of each form in our cohort of 154 families. Acoustic function in the groups of various forms of ataxia with multiple system atrophy of cerebellar predominance (MSA-C), cortical cerebellar atrophy (CCA), and hereditary ataxias including SCA31 was evaluated by using audiogram and brainstem auditory evoked potentials (BAEPs).

RESULTS

Genetic analysis of dominant ataxia families revealed that a frequency of SCA31 in our cohort was fewer than that reported from other areas of Japan, indicating that SCA31 is not widely distributed throughout Japan. Results of audiogram showed no significant difference of hearing levels among ataxic groups, and those of BAEPs did not support inner ear dysfunction in SCA31 in which hearing loss had initially been suggested as one of its characteristic symptoms.

CONCLUSION

This study suggests that acoustic impairment is neither specific to SCA31, MSA-C and CCA nor useful in making a differential diagnosis among them.

Analysis of an insertion mutation in a cohort of 94 patients with spinocerebellar ataxia type 31 from Nagano, Japan

Spinocerebellar ataxia type 31 (SCA31) is a recently defined subtype of autosomal dominant cerebellar ataxia (ADCA) characterized by adult-onset, pure cerebellar ataxia. The C/T substitution in the 5′-untranslated region of the puratrophin-1 gene (PLEKHG4) or a disease-specific haplotype within the 900-kb SCA31 critical region just upstream of PLEKHG4 has been used for the diagnosis of SCA31. Very recently, a disease-specific insertion containing penta-nucleotide (TGGAA)_n repeats has been found in this critical region in SCA31 patients. SCA31 was highly prevalent in Nagano, Japan, where SCA31 accounts for approximately 42% of ADCA families. We screened the insertion in 94 SCA31 patients from 71 families in Nagano. All patients had a 2.6- to 3.7-kb insertion. The size of the insertion was inversely correlated with the age at onset but not associated with the progression rate after onset. (TAGAA)_n repeats at the 5′-end of the insertion were variable in number, ranging from 0 (without TAGAA sequence) to 4. The number of (TAGAA)_n repeats was inversely correlated to the total size of the insertion. The number of (TAGAA)_n repeats was comparatively uniform within patients from the three endemic foci in Nagano. Only one patient, heterozygous for the C/T substitution in PLEKHG4, had the insertions in both alleles; they were approximately 3.0 and 4.3 kb in size. Sequencing and Southern hybridization using biotin-labeled (TGGAA)₅ probe strongly indicated that the 3.0-kb insertion, but not the 4.3-kb insertion, contained (TGGAA)_n stretch. We also found that 3 of 405 control individuals (0.7%) had the insertions from 1.0 to 3.5 kb in length. They were negative for the C/T substitution in PLEKHG4, and neither of the insertions contained (TGGAA)_n stretch at their 5′-end by sequencing. The insertions in normal controls were clearly detected by Southern hybridization using (TAAAA)₅ probe, while they were not labeled with (TGGAA)₅ or (TAGAA)₅ probe. These data indicate that control alleles very rarely have a nonpathogenic large insertion in the SCA31 critical region and that not only the presence of the insertion but also its size is not sufficient evidence for a disease-causing allele. We approve of the view that (TGGAA)_n repeats in the insertion are indeed related to the pathogenesis of SCA31, but it remains undetermined whether a large insertion lacking (TGGAA)_n is nonpathogenic.