Hyperphenylalaninemia (HPA) comprises a group of genetically heterogeneous disorders, including deficiencies in PAH, tetrahydrobiopterin (BH4), and DNAJC12 [2], which are associated with six genes (PAH, PTS, GCH1, QDPR, PCBD1, and DNAJC12). This evidence concerns the gene GCH1 and pulmonary arterial hypertension.