Identifying novel polymorphisms in the canine tryptophan hydroxylase 2 gene

Tryptophan hydroxylase (TPH) serves as the rate-limiting enzyme in the biosynthesis of serotonin, and two forms of TPH genes, TPH1 and TPH2, have been reported with specific nucleotide sequences and expression patterns. We determined the sequences of these two genes and identified polymorphisms within their coding regions. We identified five novel single nucleotide polymorphisms in the TPH2 gene, one of which resulted in a non-synonymous mutation and the remaining four in synonymous mutations. Comparison of the genotype frequencies of the polymorphisms among five popular breeds with different behavioral traits revealed statistically significant interbreed differences for three polymorphisms. These results suggest that these polymorphisms would be useful genetic markers when performing behavior studies in dogs.