Huntington's disease (HD) is a progressive neurodegenerative disease linked to abnormally expanded CAG repeats in the first exon of the IT15 gene. Neither HD or other glutamine expansion triplet disease has not yet been described in other species as human. In this study, we sequenced the region containing the CAG repeat expansion region of the corresponding IT15 gene in several mammalian species. In all investigated species, the number of CAG found is equal or inferior to the normal range of human IT15 alleles. The longer uninterrupted CAG stretch was found in the pig and consists of 18 CAG. In the other species, the CAG stretch was shorter and/or interrupted by other triplets. The proline encoding region following the CAG stretch is conserved in the mammalian species studied here and the number of proline is few or not reduced compared to the number of the glutamine codon repeats region.