ABSTRACT. Dynamic mutation involves the expansion of a tandem arrayed DNA sequence that is polymorphic in the population. This mechanism 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 heterozygosis was 53% (SCA1) and 8% (SCA2).

Key words: Spinocerebellar ataxia, Dynamic mutation, SCA1, SCA2, Genetic polymorphism