The development of a reliable PCR assay for genetic testing of spinocerebellar ataxia type 3. Touchdown PCR conditions were tested and different primer sets were evaluated with genomic DNA from blood sample of patients suffering from spinocerebellar ataxia type 3 (SCA3). An improved PCR assay was developed with a new set of primers and using the optimized touchdown PCR protocol. This new assay had been successfully employed in the screening of one identificated SCA3 family. Results from the present study document a simple and reliable PCR assay for genetic testing of SCA3. Strategies used in the present study may find applications in the optimization of PCR assay for triplet expansion with GC rich in the sequence context.