IDO1 and tricho-dento-osseous syndrome: KYN/TRP ratio, a clinical index of TDO/IDO1 activity (Fig. 2a) and AA/KYN ratio, reflecting KYNU A activity (Fig. 2c) were increased in AIT compared to CON (p < 0.05 and p < 0.01; respectively), whereas KYNA/KYN ratio, reflecting KAT activity (Fig. 2b) and particularly 3HAA/AA ratio, illustrating anthranilate-3-hydroxylase activity (A3H)12 (Fig. 2e) were significantly reduced in the patients’ group compared to healthy women (p < 0.05 and p < 0.001; respectively).