We read with interest the article by P. Jagota et al. entitled “Movement Disorders Commonly Seen in Asians.” In this study, the authors listed the genetic movement disorders that are known to be more common in Asians or that are frequently reported in this population. A total of 14 genetic movement disorders have been identified: Wilson's disease; spinocerebellar ataxias (SCA) types 12, 31, and 36; Gerstmann–Sträussler–Scheinker disease; PLA2G6‐related parkinsonism; adult‐onset neuronal intranuclear inclusion disease; paroxysmal kinesigenic dyskinesia; X‐linked dystonia parkinsonism; dentatorubral‐pallidoluysian atrophy (DRPLA); Woodhouse–Sakati syndrome; benign adult familial myoclonic epilepsy; Kufor‐Rakeb disease; and tremulous dystonia associated with the variant of the calmodulin‐binding transcription activator 2 gene. 1
The most common SCA subtypes in Japan are SCA3, SCA6, and SCA31, and DRPLA. SCA6/CACNA1A (MIM 183086) is the third most prevalent subtype of SCA, especially in Japan, Taiwan, Australia, Germany, the UK, and the USA. 2 On the contrary, previous studies of Brazilian patients have shown that SCA6 is relatively uncommon with a prevalence of 1.9 among all SCA. In our Ataxia Unit in Brazil, 1225 patients with different types of ataxias have been followed over the past 16 years (unpublished data). From this series, 304 are related to SCAs. The most frequent SCA was SCA3 (52.3%), followed by SCA2 (17.7%), SCA7 (11.8%), SCA1 (9.2%), SCA6 (5.59%), SCA10 (0.98%), and SCA31 (0.98%). Of note, of the 17 patients with SCA6, 15 were found to have Japanese ancestry, and only 2 Italian ancestry. Moreover, F.A. Nascimento et al. analyzed the frequency of 460 patients with SCA from southern Brazil and found that the most frequent type was SCA3 (45.7%), followed by SCA10 (18.3%), SCA2 (6.5%), SCA1 (4.3%), SCA7 (1.8%), and SCA6 (0.65%). Again, all SCA6 subjects (3 patients) were of Japanese ancestry. 3
In our SCA6 series comprising 17 patients, all had pure cerebellar ataxia and presented with a very late onset, but 1 from Japanese ancestry had parkinsonism and dopaminergic dysfunction on DAT (dopamine active transporter) scan, with partial response to levodopa. 4 In another study from our group, patients with SCA6, all from Japanese ancestry presented with more frequent respiratory events and sleep apena when compared to a control group. 5
In conclusion, SCA6 is a common genetic movement disorder in Asians. Epidemiological studies of the SCAs show marked geographical and ethnic variability, often due to diffusion by migration and founder effects in isolate populations.
Japanese immigration to Brazil started in 1908. São Paulo, Brazil, is home to the largest Japanese population outside Japan. Therefore, genetic diseases that usually affect subjects with Japanese ancestry should be strongly considered and investigated in Japanese descendants. Brazilian patients with late‐onset autosomal dominant spinocerebellar ataxia and Japanese ancestry should be tested for SCA6. We believe that this epidemiological guidance based on ancestry should also be considered in other countries.
Author Roles
(1) Research project: A. Conception, B. Organization, C. Execution; (2) Statistical analysis: A. Design, B. Execution, C. Review and critique; (3) Manuscript preparation: A. Writing of the first draft, B. Review and critique.
B.K.M.: 1A, 1B, 1C, 3A
T.Y.T.S: 1A, 3B
J.L.P.: 1A, 3B
O.G.P.B.: 1A, 3B
Disclosures
Ethical Compliance Statement: We confirm that the approval of an institutional review board was not required for this work. Informed patient consent was not necessary for this work. We confirm that we have read the journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.
Funding Sources and Conflicts of Interest: The authors report no sources of funding and no conflicts of interest.
Financial Disclosures for Previous 12 Months: The authors declare that there are no additional disclosures to report.
References
- 1. Jagota P, Lim SY, Pal PK, et al. Genetic movement disorders commonly seen in Asians. Mov Disord Clin Pract 2023;10(6):878–895. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2. Klockgether T, Mariotti C, Paulson HL. Spinocerebellar ataxia. Nat Rev Dis Primers 2019;5(1):24. [DOI] [PubMed] [Google Scholar]
- 3. Nascimento FA, Rodrigues VOR, Pelloso FC, et al. Spinocerebellar ataxias in southern Brazil: genotypic and phenotypic evaluation of 213 families. Clin Neurol Neurosurg 2019;184:105427. [DOI] [PubMed] [Google Scholar]
- 4. Pedroso JL, de Carvalho C‐NG, Speciali DS, Barsottini OG, Bor‐Seng‐Shu E, Felicio AC. Spinocerebellar ataxia type 6 presenting with parkinsonism, pre‐synaptic dopaminergic dysfunction and hyperechogenicity of the substantia nigra. J Neurol Sci 2017;376:60–62. [DOI] [PubMed] [Google Scholar]
- 5. Rueda AD, Pedroso JL, Truksinas E, Do Prado GF, Coelho FM, Barsottini OG. Polysomnography findings in spinocerebellar ataxia type 6. J Sleep Res 2016;25(6):720–723. [DOI] [PubMed] [Google Scholar]