PTS (6-pyruvoyltetrahydropterin synthase) is a metabolic enzyme that catalyzes a critical step in tetrahydrobiopterin (BH4) biosynthesis, converting 7,8-dihydroneopterin triphosphate into 6-pyruvoyl tetrahydropterin. BH4 serves as an essential cofactor for aromatic amino acid hydroxylases, which are required for the synthesis of neurotransmitters and regulation of phenylalanine metabolism. PTS localizes to both the cytoplasm and mitochondria, functioning at the intersection of amino acid metabolism and central nervous system development. Mutations in PTS cause hyperphenylalaninemia, BH4-deficient type A (also designated as segmental PTPS deficiency), a rare autosomal recessive disorder characterized by elevated plasma phenylalanine levels due to impaired BH4 availability. This leads to deficient hydroxylase activity, resulting in accumulation of phenylalanine and potential neurological complications if untreated. The clinical significance of PTS lies in its role in preventing neurotoxic effects of hyperphenylalaninemia; affected individuals typically require BH4 supplementation therapy to restore cofactor levels and normalize amino acid metabolism, preventing intellectual disability and other neurological sequelae associated with untreated disease.