Reassessment of the Role of Aromatic Amino Acid Hydroxylases and the Effect of Infection by Toxoplasma gondii on Host Dopamine

Toxoplasma gondiiinfection has been described previously to cause infected mice to lose their fear of cat urine. This behavioral manipulation has been proposed to involve alterations of host dopamine pathways due to parasite-encoded aromatic amino acid hydroxylases. Here, we report successful knockout and complementation of the aromatic amino acid hydroxylaseAAH2gene, with no observable phenotype in parasite growth or differentiationin vitroandin vivo. Additionally, expression levels of the two aromatic amino acid hydroxylases were negligible both in tachyzoites and in bradyzoites. Finally, we were unable to confirm previously described effects of parasite infection on host dopamine eitherin vitroorin vivo, even whenAAH2was overexpressed using theBAG1promoter. Together, these data indicate that AAH enzymes in the parasite do not cause global or regional alterations of dopamine in the host brain, although they may affect this pathway locally. Additionally, our findings suggest alternative roles for theAHHenzymes inT. gondii, sinceAAH1is essential for growth in nondopaminergic cells.

Hyperphenylalaninemia Due to Dihydropteridine Reductase Deficiency: Diagnosis by Measurement of Oxidized and Reduced Pterins in Urine

Hyperphenylalaninemia due to dihydropteridine reductase deficiency results from the inability to maintain the aromatic amino acid hydroxylase cofactor, tetrahydrobiopterin, in its reduced or active form. Diagnosis of the disease is usually made by direct enzymatic assay on liver biopsies or in cultured skin fibroblasts. Evidence is presented that normal children and classic phenylketonuric children excrete mainly tetrahy-drobiopterin in their urmnes, whereas children with dihydropteridine reductase deficiency excrete only oxidized forms of biopterin. Details of a rapid high performance liquid chromatographic assay for the measurement of the various forms of biopterin in urine are presented. This assay can be used to screen for suspected dihydropteridine reductase mutants.