HAAO and congenital rubella syndrome: To support these phenomena, the Trp-derived rate-limiting enzymes aligned to these Trp-Kyn metabolites were detected, and significant reductions of TPH2 in the PFC and KAT2 in the colon were observed in CRS-treated mice, along with evident elevation of IDO1, 3HAO, and QPRT in the mouse brain and gut induced by CRS (Fig. 9C–E).