Spinocerebellar ataxia type 1 (SCA1), spinocerebellar ataxia type 2 (SCA2) and 
Machado-Joseph disease or spinocerebellar ataxia type 3 (MJD/SCA3) are three 
distinctive forms of autosomal dominant spinocerebellar ataxia (SCA) caused by 
expansions of an unstable CAG repeat localized in the coding region of the 
causative genes. Another related disease, dentatorubropallidoluysian atrophy 
(DRPLA) is also caused by an unstable triplet repeat and can present as SCA in 
late onset patients. We investigated the frequency of the SCA1, SCA2, MJD/SCA3 
and DRPLA mutations in 328 Brazilian patients with SCA, belonging to 90 
unrelated families with various patterns of inheritance and originating in 
different geographic regions of Brazil. We found mutations in 35 families (39%), 
32 of them with a clear autosomal dominant inheritance. The frequency of the 
SCA1 mutation was 3% of all patients; and 6% in the dominantly inherited SCAs. 
We identified the SCA2 mutation in 6% of all families and in 9% of the families 
with autosomal dominant inheritance. The MJD/SCA3 mutation was detected in 30% 
of all patients; and in the 44% of the dominantly inherited cases. We found no 
DRPLA mutation. In addition, we observed variability in the frequency of the 
different mutations according to geographic origin of the patients, which is 
probably related to the distinct colonization of different parts of Brazil. 
These results suggest that SCA may be occasionally caused by the SCA1 and SCA2 
mutations in the Brazilian population, and that the MJD/SCA3 mutation is the 
most common cause of dominantly inherited SCA in Brazil.