title: Frequencies of spinocerebellar ataxia subtypes in Thailand: window to the population history?
abstract: Spinocerebellar ataxias (SCAs) are a heterogeneous group of disorders with almost 30 subtypes. The prevalence and relative frequency of each subtype vary among different populations. In this article, we report the relative frequency of six SCA subtypes in the Thai population and attempt to explain the observed pattern when compared with other populations in this region. We searched for SCA type 1, SCA2, SCA3, SCA6, SCA7 and dentatorubral-pallidoluysian atrophy mutations using GeneScan analysis in 340 patients from 182 families, in which at least one person had a clinical diagnosis of SCA. We analyzed the relative frequencies of SCA subtypes on a family basis, and compared these with the data in the Chinese and Indian populations. SCA3 was found in 19.2% of the patients (Agresti-Coull 95% confidence interval: 14.1-25.6%), SCA1 in 11.5% (7.6-17.1%) and SCA2 in 10.4% (6.7-15.8%). SCA6 was found in three families, with a relative frequency of 1.6% (0.3-5.0%). Compared with the related populations, the Thai SCA3 frequency was less than that of the Chinese, whereas it was higher than that in most of the Indian studies. The reverse is true for the SCA1/SCA2 frequency. A similar study in Singapore, where there was a clear history of population admixture, also showed the frequencies between those of the Chinese and the Indian populations. Although SCA3 was the most common identifiable SCA subtype in Thailand, SCA1 and SCA2 were also relatively common. Our results also supported some degree of admixture with the Indians in the Thai population and justify further study in the area.
authors.affiliation: Division of Medical Genetics and Molecular Medicine, Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Thanyachai
authors.initials: T
authors.lastname: Sura
authors.forename: Jakris
authors.initials: J
authors.lastname: Eu-Ahsunthornwattana
authors.forename: Supak
authors.initials: S
authors.lastname: Youngcharoen
authors.forename: Manisa
authors.initials: M
authors.lastname: Busabaratana
authors.forename: Donniphat
authors.initials: D
authors.lastname: Dejsuphong
authors.forename: Objoon
authors.initials: O
authors.lastname: Trachoo
authors.forename: Supischa
authors.initials: S
authors.lastname: Theerasasawat
authors.forename: Atchara
authors.initials: A
authors.lastname: Tunteeratum
authors.forename: Chinnakrit
authors.initials: C
authors.lastname: Noparutchanodom
authors.forename: Supoch
authors.initials: S
authors.lastname: Tunlayadechanont