S.F.P. Duarte et al. 360 Genetics and Molecular Research 2 (4): 360-365 (2003) www.funpecrp.com.br Genetic polymorphism at spinocerebellar ataxia 1 and 2 loci in Brazil Stenio F.P. Duarte, Raquel S. Gestinari, Mário Campos-Jr., Márcia M.G. Pimentel and Marcelo A. Costa Lima Human Genetics Service, Department of Cell Biology and Genetics, State University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil Corresponding author: M.A. Costa Lima E-mail: marlima@biologia.ufrj.br Genet. Mol. Res. 2 (4): 360-365 (2003) Received July 7, 2003 Accepted September 30, 2003 Published December 5, 2003 ABSTRACT. Dynamic mutation involves the expansion of a tandem arrayed DNA sequence that is polymorphic in the population. This mech- anism is associated with neurological/neuromuscular disorders and the pathology depends on the extension of the repeated tract, with a specific threshold for each disease. We made a PCR-based characterization of allelic polymorphism of SCA1 and SCA2 loci in a sample of 200 pairs of chromosomes in a population in Rio de Janeiro and found 23 different alleles at the SCA1 locus, varying from 10 to 39 CAG repeats (mean 27.7 ± 3.3, mode 28) and 10 different alleles ranging from 19 to 29 CAG (mean 22.1 ± 1.0, mode 22) at the SCA2 locus. The level of heterozygo- sis was 53% (SCA1) and 8% (SCA2). Key words: Spinocerebellar ataxia, Dynamic mutation, SCA1, SCA2, Genetic polymorphism Genetics and Molecular Research 2 (4): 360-365 (2003) FUNPEC-RP www.funpecrp.com.br