In vitro expression and structural analysis of four missense mutations (G247S, E280G, P362T, A434D) of phenylalanine hydroxylase gene / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To understand the pathogenic effect and the correlation between the genotype and phenotype of the 4 novel missense mutations (G247S, E280G, P362T and A434D) of phenylalanine hydroxylase gene (PAH).</p><p><b>METHODS</b>(1) The enzyme activity of the 4 mutants was assessed by using transient protein expression in mammalian cells. (2) The PAH amino acid sequences among different animal species were alignmented. (3) The effects of the 4 missense mutations on the protein structure were analyzed. (4) The clinical phenotype of the patients with PKU were analyzed, according to their blood Phe levels prior to treatment and the Phe tolerance.</p><p><b>RESULTS</b>(1) The residual enzyme activity expressed in vitro of G247S, E280G, P362T and A434D were 3.1%, 0.4%, 8.2% and 21.7% of the wild-type PAH respectively; (2)Gly247, Glu280 and Pro362 were among the highly conserved amino acids, while Ala434 was only moderately conserved; (3) As revealed by 3D structural analysis, G247S and E280G, being located at the active center of the enzyme, interfered with the binding of PAH to BH4 and ferrousion respectively, while P362T and A434D affected the formation and stability of the dimer and the tetramer of PAH; (4) As shown by clinical phenotypic analysis, classical PKU were observed in patients carrying G247S and E280G, moderate PKU were observed in patients carrying A434D, whereas both classical and moderate PKU were observed in patients carrying P362T.</p><p><b>CONCLUSION</b>(1) The E280G, G247S, P362T and A434D are all disease-causing mutations, with those located at the center of the enzyme displaying the most marked pathogenic effect; (2)The results of the structural analysis of the 3D molecule are consistent with the activity assessment of the enzyme expressed in vitro; (3) The consistency is observed between the genotype, the enzymatic activity expressed in vitro and the clinical phenotype.</p>

Pterin & DHPR measurement and DNA analysis in Korean PKU patients

Phenylketonuria is metabolic disorder that results from a deficiency of the hepatic phenylalanine hydroxylase. But among patients with hyperphenylalaninemia, the defect resides in one of the enzymes necessary for production or recycling of tetrahydrobiopterin (BH4). The reduction of BH4 affects not only phenylalanine metabolism but also formation of the tyrosine related neurotransmitter, dopamin and tryptophan related neurotransmitter, serotonin. Administration of L-dopa and 5-hydroxytriptophan seems to be the most effective treatment and may prevent irreversible neurologic damage if started early in life in hyperphenylalaninemia due to deficiency of cofactor BH4. Therefore, all patients with PKU and hyperphenylalaninemia should be tested for BH4 deficiency as early as passible. So we measured reduced forms of biopterin in urines of 19 phenylketonuria patients by Funkushima and Nixon method and 13 of PKU patients measured dihydropterin reductase (DHPR) in white blood cells by modified Narisawa method. We could not find abnormal pterin patterns of cofactor BH4 and normal value of DHPR. All Korean 19 PKU children were classic PKU. A missense mutation has been identified in the phenylalanine hydroxylase (PAH) gene of 16 Koran PKU patients. 5 mutations (IVS4, Y204 C, R243Q, Y356 X, R413 P) have been identified. The frequency of these mutations was found to be 50% of PKU alleles. The IVS4 mutation had a high frequency in Korea and southern China, due to the result of the founder effect and genetic drift. the R413 P mutation, which may have originated in the regions surrounding the Baikal, expanded to northen China and Japan. We were not able to find Caucasian mutations in Korean ptiets. PKU mutations occured after racial divergence between Caucasian and Mongoloids. We observed that PKU patients with Y 204 C and R413 P mutations showed mild mild clinical phenotype but IVS4 mutation had severe mental retardation. the establishment of genotype will therefore aid in the prediction of clinical phenotypes in patients with this disease. So, pterin and DHPR measurement and DNA analsis will be useful for prognosis and proper treatment of PKU patients.