Conclusion/discussion: We demonstrated that alterations in the activity of enzymes involved in brain GSH metabolism is probably underlying the changes in GSH/GSSG ratio in HPA while reactions of phase II detoxification, represented by GST, seems to be not involved. ( Deficiency of 6-pyrovoyl-tetrahydropterin synthase is the most common cause of tetrahydrobiopterin metabolism disorders. Typical features of the disease are neuromotor signs, which are due to monoamine depletion. Isolated psychiatric symptoms are not commonly described.