Patients with disorders of BH4 metabolism including GTP cyclohydrolyase I (GTPCH) deficiency, 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, dihydropteridine reductase (DHPR) deficiency and pterin-4a-carbinolamine dehydratase (PCD) deficiency can present with any degree of HPA [19, 20]. This evidence concerns the gene QDPR and pterin-4 alpha-carbinolamine dehydratase 1 deficiency.