QDPR and GTP cyclohydrolase I deficiency with hyperphenylalaninemia: This group of BH4 disorders can be classified as of whether PHE levels are elevated or normal. Subjects with elevated PHE include pyruvoil-4Hp-pterin synthase (PTPS) deficiency, autosomal recessive GTP cyclohydroxylase (GTPCH) deficiency, dihydropteridine reductase (DHPR) deficiency, and pterin-carbinolamine reductase (PCD) deficiency.