Tetrahydrobiopterin deficiency mainly occurs because of 6-pyruvoyl tetrahydrobiopterin synthase (PTPS) deficiency caused by mutations of 6-pyruvoyltetrahydropterin synthase (PTS, NM_000317.2) (accounting for 96% in China)7, which can be distinguished from PAH deficiency by urinary pterin analysis. This evidence concerns the gene PTS and phenylketonuria.