The level of TDO expression increased with age in both mouse strains, however higher TDO immunoreactivity was observed in 6–8 month groups of 3xTg AD mice compared to age matched WT controls (1.8-fold for 7 month, 1.5-fold for 11 month), with significant difference showing in 7-month 3xTg AD mice compared to age matched WT controls (p<0.05) (Fig. 3). This evidence concerns the gene TDO2 and Alzheimer disease.