Spinocerebellar Ataxia Type 6 in Two Korean Families

Koh, Seong Ho; Noh, Hak Jae; Kim, Seung Hyun; Kim, Hee Tae; Shin, Dong Jin; Kim, Myung Kwon; Park, Sung Sup; Kim, Ji Yeon; Jeon, Beom S

Abstract

BACKGROUND: Spinocerebellar ataxia 6 (SCA6) is an autosomal dominant spinocerebellar degeneration and caused by the expansion of the polymorphic CAG repeat in the human alpha 1A voltage-dependent calcium channel subunit gene. In this study, we report the clinical and molecular genetic characteristics of SCA6 in 2 Korean families. We further describe that SCA6 and Episodic ataxia type 2 are simultaneously developed in same family showing no intergenerational changes of CAG repeat numbers.
METHODS
Seventeen members of one family and nine of the other received detailed neurological examination and history taking at least one occasion. After the screening test, molecular diagnostic test by using Zhuchenko's method were performed in 13 patients in one family and 3 in the other, respectively.
RESULTS
Normal range of CAG repeat in 92 normal individuals was 8 to 17. In this study, the numbers of CAG repeat in one family was 26 and in another was 23. There were no intergenerational differences in the numbers of CAG repeat. Despite the same number of CAG repeat, the clinical anticipation were found. Only one showed episodic ataxia clinically.
CONCLUSIONS
Comparing with other types of SCA, the SCA6 had several remarkable characteristics: 1) very small CAG expansions (21-27 repeats) lead to clinical symptoms and the repeat numbers are relatively stable, 2) clinical anticipation is observed despite the relatively stable repeat on intergenerational transmission. The finidngs that an EA2 and a SCA6 exist in a same family may be suggest that two disease are the same disorder with a high phenotypic variablity.