Objective: The 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is the most common type of tetrahydrobiopterin (BH4) deficiency. The reported patients with BH4 deficiency are all PTPS deficient found in the mainland of China previously. The activity of dihydropteridine reductase in BH4 metabolism has been determined for 902 patients with hyperphenylalaninemia in the authors' laboratory since 2003. The purposes of this study were to characterize the first case with DHPR deficiency who was diagnosed in June, 2007, to investigate the clinical manifestation, the differential diagnostic criteria, the effect of treatment as well as gene mutation of DHPR deficiency.
Methods: (1) A male patient presented with poor hand control, seizure, hypotonia and mental retardation since five-month after birth. His phenylalanine (Phe) level was 600 micromol/L and he was diagnosed as hyperphenylalaninemia at the age of one year and six-month. (2) This patient was subjected to combined Phe (100 mg/kg) and BH4 (20 mg/kg) loading test, to evaluate the degree of Phe level response to BH4. Urinary neopterin and biopterin analysis as well as the determination of DHPR activity in dried blood spot were also performed. (3) The blood DNA samples of the patient and his parents were collected to amplify the seven exons of QDPR gene using related primers, and the amplified products were directly sequenced for mutation analysis. (4) The patient was treated with BH4 or with a combined small amount of Phe-free special milk, neurotransmitter precursors and folic acid after the diagnosis and was followed up for clinical effects of treatment.
Results: (1) The basic Phe level was 476 micromol/L, then it increased to 1355 micromol/L at 3 h after taking Phe and slowly decreased to 610 micromol/L at 24h after taking BH4. (2) The basic urinary neopterin and biopterin were 2.92 mmol/mol Cr (normally < 2.61 mmol/mol Cr) and 7.44 mmol/molCr (normally < 2.67 mmol/mol Cr) respectively, and biopterin percentage was 71.79% (normally 42.7% - 75.9%). The patient had higher biopterin level. (3) The DHPR activity of this patient was (0.27 - 0.51) nmol/(min.5 mm disc) which were 6.11% - 10.6% of normal control, so he was diagnosed as DHPR deficiency. (4) The analysis of QDPR gene mutation showed that the patient carries missense mutation c.515C > T (P172L) from his father and nonsense mutation c.661C > T (R221X) from his mother. The c.515C > T is not reported before, we also did not find this mutation in 50 normal children. (5) The patient started to be treated with large dosage of BH4 (10 - 20) mg/(kg.d) or BH4 combined with small amounts of Phe-free milk, neurotransmitter precursors L-dopa (3 - 5) mg/(kg.d) plus carbidopa, 5-hydroxytryptophan (3 - 5) mg/(kg.d), and folic acid 15 mg/d as well at the age of one year and six-month after the diagnosis. The seizure has disappeared, the symptoms such as hypotonia have been obviously improved and the Phe level was 60 micromol/L at the six months after the treatment in this patient.
Conclusion: (1) The patient with DHPR deficiency has common symptoms of BH4 deficiency (such as fair hair, hypotonia, mental retardation), and there is metabolic disturbance of folic acid in DHPR deficiency. (2) The higher Phe levels slowly decreased after BH4 loading test, the urinary biopterin level was very high and the DHPR activity was very low in the patient with DHPR deficiency. (3) The c.515C > T may be a new mutation of QDPR gene. (4) The DHPR deficient patient must be treated with higher dose of BH4 (8 - 20) mg/(kg.d), neurotransmitter precursors and folic acid as well.