二氢蝶啶还原酶缺乏症一例的诊治及基因突变分析

Diagnosis, treatment and gene mutation analysis of the first case with dihydropteridine reductase deficiency in the mainland of China

目的探讨二氢蝶啶还原酶（DHPR）缺乏症的临床诊治和基因突变分析。方法（1）归纳、总结临床症状、体征，血苯丙氨酸（Phe）浓度；（2）进行Phe（100mg／kg）十四氢生物蝶呤（BH4）（20mg／kg）负荷试验、尿蝶呤谱分析及红细胞DHPR测定；（3）进行DHPR基因QOPR突变检测；（4）采用BH4、神经递质前质等治疗，随访疗效。结果（1）患儿男，生后5个月出现抬头困难、头发黄、抽搐、肌张力低下。生后1岁6个月Phe 600 μm0L／L；（2）负荷试验前血Phe浓度476 μmoL／L，Phe负荷3h上升至1355 μmoL／L，BH4负荷24h血Phe浓度缓慢降至610 μmoL／L；（3）尿新蝶呤2．92mmoL／mol肌酐，生物蝶呤7．44mmol/mol肌酐，生物蝶呤百分比71．79％；（4）DHPR活性（0．27～0．51）nmol/（min·5mm disc），为正常对照的6．11％～10．60％，诊断为DHPR缺乏症；（5）患儿QDPR基因突变类型为c．515C〉T及c．661C〉T，c．515C〉T突变未见报道；（6）患儿普食下接受BH4（10～20）mg/（kg·d）或联合少量无Phe奶粉、神经递质前质L-DOPD（3～5）mg／（kg·d）（联合carbidopa）、5羟色氨酸（3～5）mg／（kg·d）及叶酸15mg／d治疗。治疗6个月症状明显改善，抽搐停止、会扶走，血Phe60μmoL／L。结论（1）DHPR缺乏症具有肌张力低下等BH。缺乏症共同特点；（2）BH4负荷后血Phe浓度下降缓慢；尿生物蝶呤增高，DHPR活性低下是确诊依据；（3）c．515C〉T（P172L）是QOPR基因新的致病突变；（4）神经递质前质、叶酸及大剂量BH4（或联合无Phe奶粉）治疗疗效显著。

Objective The 6-pyruvoyl-tetrahydropterin synthase （FIPS） 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 μmol/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 μmol/L, then it increased to 1355 μmol/L at 3 h after taking Phe and slowly decreased to 610 μmol/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 - 0.5 l ） 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） ms/（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 μmol/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） ms/（ kg · d）, neurotransmitter precursors and folic acid as well.