Frequency analysis of autosomal dominant cerebellar ataxias in Taiwanese patients and clinical and molecular characterization of spinocerebellar ataxia type 6.

BACKGROUND: Spinocerebellar ataxia (SCA) is a heterogeneous group of neurodegenerative disorders. The mutational basis for most of these disorders is an expanded CAG repeat sequence within the coding regions of the genes involved. The prevalence of SCA in the ethnic Chinese on Taiwan remains unclear. Moreover, there has been no report of SCA type 6 (SCA6) among Chinese people.
OBJECTIVES: To characterize the prevalence of SCA in the ethnic Chinese on Taiwan, and to specifically characterize Chinese patients with SCA6 in terms of clinical and molecular features. PATIENTS AND METHODS: Using a molecular approach, we investigated SCA in 74 Taiwanese families with dominantly inherited ataxias and in 49 Taiwanese patients with sporadic ataxias. Clinical and molecular features of SCA6 were further characterized in 12 patients from 8 families and in 2 sporadic cases. Furthermore, the intragenic polymorphic marker D19S1150 was amplified by polymerase chain reaction to analyze for linkage disequilibrium.
RESULTS: Machado-Joseph disease-SCA3 was the most common type of autosomal dominant SCA in the Taiwanese cohort, accounting for 35 cases (47.3%), followed by SCA6 (8 [10.8%]), SCA2 (8 [10.8%]), SCA1 (4 [5.4%]), SCA7 (2 [2.7%]), dentatorubropallidoluysian atrophy (1 [1.4%]), and SCA8 (0%). The genes responsible for 16 (21.6%) of Taiwanese dominantly inherited SCA cases remain to be determined. Among the 49 patients with sporadic ataxias in the present series, 2 (4.1%) were found to harbor SCA6 mutations. In the families with SCA6, we found significant anticipation in the absence of genetic instability on transmission, indicating that some other mechanism might account for the anticipation. The same frequent allele of the intragenic DNA marker (D19S1150) was shared by 7 of 10 Taiwanese families with SCA6.
CONCLUSIONS: Although SCA6 has, so far, not been reported in mainland Chinese, we found a geographic cluster of families with SCA6 on Taiwan. Genotyping studies suggest a founder effect in the Taiwanese patients with SCA6.