QDPR gene mutation and clinical follow-up in Chinese patients with dihydropteridine reductase deficiency

Background:This study aimed to investigate the mutation spectrum of the QDPR gene,to determine the effect of mutations on dihydropteridine reductase(DHPR)structure/function,to discuss the potential genotype-phenotype correlation,and to evaluate the clinical outcome of Chinese patients after treatment.Methods:Nine DHPR-deficient patients were enrolled in this study and seven of them underwent neonatal screening.QDPR gene mutations were analyzed and confi rmed by routine methods.The potential pathogenicity of missense variants was analyzed using Clustal X,PolyPhen program and Swiss-PDB Viewer 4.04_OSX software,respectively.The clinical outcomes of the patients were evaluated after long-term treatment.Results:In 10 mutations of the 9 patients,4 were novel mutations(G20V,V86D,G130S and A175R),4 were reported by us previously,and 2 known mutations were identified.R221X was a hotspot mutation(27.7%)in our patients.Eight missense mutations probably had damage to protein.Six patients in this series were treated with a good control of phenylalanine level.The height and weight of the patients were normal at the age of 4 months to 7.5 years.Four patients,who underwent a neonatal screening and were treated early,showed a normal mental development.In 2 patients diagnosed late,neurological symptoms were signifi cantly improved.Conclusions:The mutation spectrum of the QDPR gene is different in the Chinese population.Most mutations are related to severe phenotype.The determination of DHPR activity should be performed in patients with hyperphenylalaninemia.DHPR-defi cient patients who were treated below the age of 2 months may have a near normal mental development.

Protective effect of dihydropteridine reductase against oxidative stress is abolished with A278C mutation

Objective: To evaluate the antioxidation of dihydrobiopterin reductase and to explore the effect of A278C mutation of the quinoid dihydropteridine reductase(QDPR) gene on its antioxidant activity. Methods: First, plasmids with different genes(wild and mutant QDPR) were constructed. After gene sequencing, they were transfected into human kidney cells(HEK293T). Then, the intracellular production of reactive oxygen species(ROS) and tetrahydrobiopterin(BH4) was detected after cells were harvested. Activations of nicotinamide adenine dinucleotide phosphate oxidase 4(NOX4), glutathione peroxidase 3(GPX3), and superoxide dismutase 1(SOD1) were analyzed to observe the oxidative stress after transfection. The expression of the neuronal nitric oxide synthase(n NOS) gene was analyzed by semiquantitative reverse-transcription polymerase chain reaction(RT-PCR). We also detected the activation of transforming growth factor β1(TGF-β1) by enzyme-linked immunosorbent assay(ELISA) to observe the connection of TGF-β1 and oxidative stress. Results: The exogenous wild-type QDPR significantly decreased the expression of n NOS, NOX4, and TGF-β1 and induced the expression of SOD1 and GPX3, but the mutated QDPR lost this function and resulted in excessive ROS production. Our data also suggested that the influence on the level of BH4 had no significant difference between mutated and the wild-type QDPR transfection. Conclusions: Wild-type QDPR played an important role in protecting against oxidative stress, but mutant QDPR failed to have these beneficial effects.