Globally, PTPS deficiency is the most frequent BH4 deficiency (≈54%), followed by dihydropteridine reductase (DHPR) deficiency (≈33%).[23] However, in China, PTPS deficiency accounts for ≈96% of BH4 deficiencies, followed by DHPR deficiency (2.4%) and guanosine triphosphate cyclohydrolase I (GTPCH) deficiency (1.6%).[24] Notably, the prevalence of BH4 deficiency is 3.8 per 1 000 000 live births in China.[25] These reasons resulted in almost no BH4 samples with PTPS deficiency, GTPCH deficiency, and other types of BH4 deficiencies except for PTPS deficiency being collected in the hospital. Here, PTS is linked to GTP cyclohydrolase I deficiency with hyperphenylalaninemia.