Four Years of Diagnostic Challenges with Tetrahydrobiopterin Deficiencies in Iranian Patients

Hyperphenylalaninemia (HPA) is a condition caused by tetrahydrobiopterin (BH₄) and phenylalanine hydroxylase (PAH) deficiencies. It is essential that differential diagnosis be conducted to distinguish these two causes of HPA, because BH₄ deficiency is a more severe disease involving progressive neurologic deterioration. Based on the biological findings, HPA is defined as a plasma phenylalanine level of >2.0 mg/dl (>120 μmol/l). The National Biochemistry Reference Laboratory at the Pasteur Institute of Iran initiated BH₄ deficiency screening tests for the first time during the implementation of a nationwide phenylketonuria (PKU) screening program. Measurement of blood phenylalanine and urinary neopterin and biopterin was conducted by high-performance liquid chromatography in 617 patients with HPA. Dihydropteridine reductase (DHPR) activity was measured in all patients by kinetic spectrophotometry. Differential diagnosis was conducted for PKU, transient HPA, and BH₄ deficiencies.Our results indicated that out of 76 cases involving BH₄ deficiencies, 37 had 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, 35 had DHPR deficiency, 1 case had pterin-4a-carbinolamine dehydratase (PCD) deficiency, and 3 cases had GTP cyclohydrolase I (GTPCH) deficiency. In this study, 1 novel deletion mutation and 18 novel missense mutations were reported in addition to mutations that had previously been identified and registered in BIOMDB. At present, the screening program for PKU in Iran includes tests that detect different forms of BH₄ deficiency presenting with HPA. Newborns that are BH₄-deficient benefit from the availability of the tests because they can receive necessary care before being clinically affected.