Spinocerebellar ataxia (SCA) is inherited neurodegenerative disorders in associated with progressive cerebellar degeneration affecting worldwide populations. Causative genetic defects underlying SCA are extensively heterogeneous, which types and prevalence of SCA are widely varied among different populations. In Thailand, almost 90 % of familial SCA families, and over 30 % of sporadic cases are Machado-Joseph disease (MJD, or SCA3), SCA1, SCA2 and SCA6 [
1]. In contrast, SCA7 and dentatorubro-pallidoluysian atrophy (DRPLA) have not been observed to date. Since some other uncommon types of SCA have been described in multiple ethnics, those certain types are merit for further screening in the Thai patients [
2]. The study was interested in investigating some uncommon SCAs including SCA8, SCA10, SCA12, SCA17 and SCA19.
SCA8 is caused by bidirectional transcribed of CTG-CAG repeat-expansion mutation of ataxin 8 opposite strand (
ATXN8OS), and ataxin 8 (
ATXN8) on chromosome 13q21 [
3]. The disease is transmitted in autosomal dominant fashion with often reduced penetrance [
4]. Patients present as a slowly progressive cerebellar syndrome frequently accompanied with pyramidal signs [
4,
5]. SCA10 is an autosomal dominant ataxia often accompanied with epilepsy caused by an expansion of a pentanucleotide (ATTCT) repeat in intron 9 of
ATXN10. The disease is exclusively identified in Amerindian descents mainly in South America, in which they are likely to share a common ancestral origin [
6,
7]. SCA12 is caused by a CAG repeat expansion in a promoter region of the
PPP2R2B on chromosome 5q32 [
8]. Action tremor is often a prominent feature. Apart from Caucasians, SCA12 is also identified as an infrequent cause of SCA in Indians and Chinese [
9‐
11]. SCA17 is caused by an abnormal CAG/CAA repeat expansion in TATA-binding protein gene (
TBP) [
12]. Various additional features including parkinsonism, chorea, dystonia and dementia is common. Although SCA17 regards as an uncommon type of SCA, the disease is described in quite a few populations including in East Asian [
13,
14]. Furthermore, the pathological repeat-expansion alleles of SCA17 were also observed in association with Parkinson’s disease (PD) in Taiwanese and Korean, implying the occurrence of SCA17 might be relatively common in East Asian [
15,
16]. SCA19 and SCA22 were originally described in Dutch and Han Chinese families, respectively. Both diseases were mapped to the same locus on chromosome 1q [
17]. Their phenotypes were similar in some extents, which they often present as a very slowly progressive ataxia with frequent hyporeflexia. However, additional features including Holmes tremor, myoclonus and impairment of proprioceptive sensation were only observed in some cases of the Dutch family [
18,
19]. Recently, a voltage-gated potassium channel Kv4.3-encoding gene (
KCND3) was described as a causative gene responsible for both SCA19 and SCA22 [
20,
21].
The study attempted to identify the SCA subtypes in Thai patients without any known genetic mutations, and defined their genotype-phenotype correlations. SCA8, SCA12, SCA17, and SCA19/22 were designated to analyse because they were described in multiple populations. Since a few of the studied patients had epilepsy as an additional feature, SCA10 was designated to investigate as a candidate gene.