Chromosomal localization, genomic structure and characterization of the human gene and a retropseudogene for 6-pyruvoyltetrahydropterin synthase

Identification and molecular analysis of 11 cases of the PTS gene variants associated with tetrahydrobiopterin deficiency

Background: Tetrahydrobiopterin deficiency (BH4D) is a rare autosomal recessive amino acid metabolic disease that belongs to a kind of hyperphenylalaninemia (HPA), and 6-pyruvyltetrahydrotrexate synthase (PTPS) deficiency is the most common type of BH4D. This study investigates the clinical and genetic characteristics of 11 PTPS deficiency cases in the Beijing area, identifies the genetic pathogenic factors, and evaluates the value of high-throughput sequencing in the precise diagnosis of PTPS deficiency.

Methods: The Beijing Neonatal Disease Screening Center diagnosed patients with HPA. The study used phenylalanine (Phe) in blood, the ratio of Phe to Thr, urotrexate spectrum analysis, erythrocyte dihydrotrexate reductase (DHPR) activity determination, and high-throughput sequencing as methods. Bioinformatics software analyzed the variants’ pathogenicity and used RT-PCR to identify deep intron variants’ pathogenicity.

Result: Among 635 cases with HPA, 38 cases were diagnosed with BH4D, of which the incidence in HPA was 5.98%. Nine kinds of PTS gene variants were detected, including seven missense variants, one splicing variant, and one deletion variant. The splicing variant c.84–291A>G had three splicing results in vivo: normal length, 79bp pseudoexon insertion, and exon 3 skipping. Bioinformatics and Sanger sequencing were performed to verify the identified variants.

Conclusion: High-throughput sequencing is a helpful tool for clinical diagnosis and differential diagnosis of BH4D. This study confirms that c.84–291A>G is the hot spot variant of PTPS deficiency, and it is the first reported variant with a new splicing pattern in vivo. A novel deletion variant c.84_163del (p.Lys29Cysfs∗9) was found to enrich the genetic variant spectrum of the disease.

Improvement of Diagnostic Yield by an Additional Amplicon Module to Hybridization-Based Next-Generation Sequencing Panels

Many approaches aimed at improving next-generation sequencing output for clinical purposes exist. However, sequencing gaps or misalignments for regions that are difficult to cover because of their low complexity or high homology still exist. The aim of this study was to improve the yield of sequencing data. A hybridization-based next-generation sequencing library was pooled with custom add-on amplicon-based libraries processed by the same commercial test and run in parallel and sequenced simultaneously. Formulas and steps for proper amplicon pooling (250 to 7000 bp) and final library merging are presented. The novel strategy was tested on selected archetypal situations: diagnostics of a gene with many pseudogenes, a genomic region surrounded by Alu repeats, simple one-time addition of an extra gene, and mosaicism detection. The sequence of all supplemented genomic regions was traced with reasonable coverage at the background of a hybridization captured library. The flexible add-on module expands the possibilities of routine diagnostics. The technical solution makes it possible to mix amplicons that differ significantly in size and process them in one tube simultaneously with samples of the hybridization-based panel. The proposed approach reduces turnaround time and increases diagnostic yield.

Clinical, biochemical and molecular spectrum of mild 6-pyruvoyl-tetrahydropterin synthase deficiency and a case report

Background 6-Pyruvoyl-tetrahydropterin synthase (PTS) is the key enzyme in BH4 synthesis. PTS deficiency is classified as severe type and mild type, and the prognosis and treatment differ for these types. Distinguishing between two types in the early stage is difficult. Reference to reported cases is needed for interpretation of the correlation between genotype and prognosis. Case report: We report a full-term female newborn with mild PTS deficiency. On the day 21 after birth, the phenylalanine level was 859.6 mmol/L (reference range: 30-117 mmol/L). After 1 year of observation, the patient was found to be in a healthy condition without treatment. Conclusions: Although the phenylalanine level is high in mild PTS deficiency patients after birth, some of them may have few symptoms with no treatment. We review 19 cases and find 8 mutations of PTS that may be associated with mild PTS deficiency.

Molecular and metabolic bases of tetrahydrobiopterin (BH4) deficiencies

Tetrahydrobiopterin (BH4) deficiency is caused by genetic variants in the three genes involved in de novo cofactor biosynthesis, GTP cyclohydrolase I (GTPCH/GCH1), 6-pyruvoyl-tetrahydropterin synthase (PTPS/PTS), sepiapterin reductase (SR/SPR), and the two genes involved in cofactor recycling, carbinolamine-4α-dehydratase (PCD/PCBD1) and dihydropteridine reductase (DHPR/QDPR). Dysfunction in BH4 metabolism leads to reduced cofactor levels and may result in systemic hyperphenylalaninemia and/or neurological sequelae due to secondary deficiency in monoamine neurotransmitters in the central nervous system. More than 1100 patients with BH4 deficiency and 800 different allelic variants distributed throughout the individual genes are tabulated in database of pediatric neurotransmitter disorders PNDdb. Here we provide an update on the molecular-genetic analysis and structural considerations of these variants, including the clinical courses of the genotypes. From a total of 324 alleles, 11 are associated with the autosomal recessive form of GTPCH deficiency presenting with hyperphenylalaninemia (HPA) and neurotransmitter deficiency, 295 GCH1 variant alleles are detected in the dominant form of L-dopa-responsive dystonia (DRD or Segawa disease) while phenotypes of 18 alleles remained undefined. Autosomal recessive variants observed in the PTS (199 variants), PCBD1 (32 variants), and QDPR (141 variants) genes lead to HPA concomitant with central monoamine neurotransmitter deficiency, while SPR deficiency (104 variants) presents without hyperphenylalaninemia. The clinical impact of reported variants is essential for genetic counseling and important for development of precision medicine.

6-Pyruvoyltetrahydropterin Synthase Deficiency: Review and Report of 28 Arab Subjects

BACKGROUND

Tetrahydrobiopterin is an essential cofactor for the hydroxylation of aromatic amino acids phenylalanine, tyrosine, and tryptophan. Therefore, tetrahydrobiopterin deficiency results in hyperphenylalaninemia as well as dopamine and serotonin depletion in the central nervous system. The enzyme 6-pyruvoyltetrahydropterin synthase catalyzes the second step of de novo synthesis of tetrahydrobiopterin, and its deficiency is the most frequent cause of tetrahydrobiopterin metabolism disorders.

METHOD

We conducted a retrospective chart review of 28 subjects from 24 families with molecularly confirmed 6-pyruvoyltetrahydropterin synthase deficiency from six centers in three Arab countries. We reviewed clinical, biochemical, and molecular data. We also reviewed previously published cohorts of subjects with 6-pyruvoyltetrahydropterin synthase deficiency.

RESULTS

Similar to previous observations, we show that early treatment (less than two months) is associated with better outcome. We identify eight PTS variants in 24 independent families. The most common variant is (c.238A>G; p.M80V) with an allele count of 33%. We also identify one novel variant (c.2T>G; p.?).

CONCLUSION

The deficiency of 6-pyruvoyltetrahydropterin synthase is relatively common in the Arab population and should be considered in individuals with hyperphenylalaninemia. More natural history studies with comprehensive biochemical and molecular genetics data are needed for a robust base for the development of future therapy.

Genetic determinants involved in the biodegradation of naphthalene and phenanthrene in Pseudomonas aeruginosa PAO1

Pseudomonas sp. are predominant isolates of degradation-competent strains while very few studies have explored the degradation-related genes and pathways in most of the degrading strains. P. aeruginosa PAO1 was found capable of degrading naphthalene and phenanthrene efficiently. In order to investigate the degradation-related genes of naphthalene and phenanthrene in P. aeruginosa PAO1, a random promoter library of about 5760 strains was constructed. Thirty-two clones for differentially expressed promoters were obtained by screening in the presence of sub-inhibitory concentration of naphthalene and phenanthrene. Among them, 13 genes were up-regulated and 15 were down-regulated in the presence of naphthalene as well as phenanthrene. The four remaining genes have different regulation tendencies by naphthalene or phenanthrene. By comparing the growth between the wild type and mutants as well as the complementations, the roles of seven selected up-regulated genes on naphthalene and phenanthrene degradation were investigated. Five of the seven selected up-regulated genes, like PA2666 and PA4780, were found playing key roles on the degradation in P. aeruginosa PAO1. Also, the results imply that these genes participate in the overlapping part of naphthalene and phenanthrene degradation pathways in PAO1. Results in the article offer the convenience quick method and platform for searching degradation-related genes. It also laid a foundation for understanding of the role of the regulated genes.

Transposable element-driven transcript diversification and its relevance to genetic disorders

The human genome project and subsequent gene annotation projects have shown that the human genome contains 22,000-25,000 functional genes. Therefore, it is believed that the diversity of protein repertoire is achieved by the alternative splicing (AS) mechanism. Transposable elements (TEs) are mobile in nature and can therefore alter their position in the genome. The insertion of TEs into a new gene region can result in AS of a particular transcript through various mechanisms, including intron retention, and alternative donor or acceptor splice sites. TE-derived AS is thought to have played a part in primate evolution and in hominid radiation. However, TE-derived AS or genetic instability may sometimes result in genetic disorders. For the past two decades, numerous studies have been performed on TEs and their role in genomes. Accumulating evidence shows that the term 'junk DNA', previously used for TEs is a misnomer. Recent research has indicated that TEs may have clinical potential. However, to explore the feasibility of using TEs in clinical practice, additional studies are required. This review summarizes the available literature on TE-derived AS, alternative promoter, and alternative polyadenylation. The review covers the effects of TEs on coding genes and their clinical implications, and provides our perspectives and directions for future research.

Alu elements: at the crossroads between disease and evolution

The cost of DNA sequencing is decreasing year by year, and the era of personalized medicine and the $1000 genome seems to be just around the corner. In order to link genetic variation to gene function, however, we need to learn more about the function of the non-coding genomic elements. The advance of high-throughput sequencing enabled rapid progress in mapping the functional elements in our genome. In the present article, I discuss how intronic mutations acting at Alu elements enable formation of new exons. I review the mutations that cause disease when promoting a major increase in the inclusion of Alu exon into mature transcripts. Moreover, I present the mechanism that represses such a major inclusion of Alu exons and instead enables a gradual evolution of Alu elements into new exons.

Mutations in the BH4-metabolizing genes GTP cyclohydrolase I, 6-pyruvoyl-tetrahydropterin synthase, sepiapterin reductase, carbinolamine-4a-dehydratase, and dihydropteridine reductase

Tetrahydrobiopterin (BH(4)) deficiencies are a highly heterogeneous group of disorders with several hundred patients, and so far a total of 193 different mutant alleles or molecular lesions identified in the GTP cyclohydrolase I (GTPCH), 6-pyruvoyl-tetrahydropterin synthase (PTPS), sepiapterin reductase (SR), carbinolamine-4a-dehydratase (PCD), or dihydropteridine reductase (DHPR) genes. The spectrum of mutations causing a reduction in one of the three biosynthetic (GTPCH, PTPS, and SR) or the two regenerating enzymes (PCD and DHPR) is tabulated and reviewed. Furthermore, current genomic variations or SNPs are also compiled. Mutations in GCH1 are scattered over the entire gene, and only 5 out of 104 mutant alleles, present in a homozygous state, are reported to cause the autosomal recessive form of inheritable hyperphenylalaninemia (HPA) associated with monoamine neurotransmitter deficiency. Almost all other 99 different mutant alleles in GCH1 are observed together with a wild-type allele and cause Dopa-responsive dystonia (DRD, Segawa disease) in a dominant fashion with reduced penetrance. Compound heterozygous or homozygous mutations are spread over the entire genes for PTS with 44 mutant alleles, for PCBD with nine mutant alleles, and for QDPR with 29 mutant alleles. These mutations cause an autosomal recessive inherited form of HPA, mostly accompanied by a deficiency of the neurotransmitters dopamine and serotonin. Lack of sepiapterin reductase activity, an autosomal recessive variant of BH(4) deficiency presenting without HPA, was diagnosed in patients with seven different mutant alleles in the SPR gene in exons 2 or 3 or in intron 2. Details on all mutations presented here are constantly updated in the BIOMDB database (www.bh4.org).

Low tetrahydrobiopterin biosynthetic capacity of human monocytes is caused by exon skipping in 6-pyruvoyl tetrahydropterin synthase

Biosynthesis of (6 R )-5,6,7,8-tetrahydro-L-biopterin (H(4)-biopterin), an essential cofactor for aromatic amino acid hydroxylases and NO synthases, is effectively induced by cytokines in most of the cell types. However, human monocytes/macrophages form only a little H(4)-biopterin, but release neopterin/7,8-dihydroneopterin instead. Whereas 6-pyruvoyl tetrahydropterin synthase (PTPS) activity, the second enzyme of H(4)-biopterin biosynthesis, is hardly detectable in these cells, PTPS mRNA levels were comparable with those of cell types containing intact PTPS activity. By screening a THP-1 cDNA library, we identified clones encoding the entire open reading frame (642 bp) as well as clones lacking the 23 bp exon 3, which results in a premature stop codon. Quantification of the two mRNA species in different cell types (blood-derived cells, fibroblasts and endothelial cells) and cell lines showed that the amount of exon-3-containing mRNA is correlated closely to PTPS activity. The ratio of exon-3-containing to exon-3-lacking PTPS mRNA is not affected by differential mRNA stability or nonsense-mediated mRNA decay. THP-1 cells transduced with wild-type PTPS cDNA produced H(4)-biopterin levels and expressed PTPS activities and protein amounts comparable with those of fibroblasts. We therefore conclude that exon 3 skipping in transcription rather than post-transcriptional mechanisms is a major cause of the low PTPS protein expression observed in human macrophages and related cell types.

[Perspectives on tetrahydrobiopterin research]

Tetrahydrobiopterin ((6R)-L-erythro-tetrahydrobiopterin, BH4) is de novo synthesized from GTP. Enzymes involved in its synthesis are the rate limiting enzyme GTP cyclohydrolase I, 6-pyruvoyl tetrahydropterin synthase (PTPS) and sepiapterin reductase. Abnormalities in the metabolism of BH4 have been demonstrated in some diseases affecting the central nervous systems such as atypical phenylketonuria, hereditary progressive dystonia (Segawa's disease). Furthermore, BH4 has been shown to be involved in vascular protection. It is suggested that the dysfunction of endothelial BH4 leads to atherosclerosis. Recently we established BH4-deficient mice by disrupting the PTPS gene to investigate the effects of BH4 depletion on the animals and the involvement of BH4 in regulating biological functions including neural systems. Investigation utilizing this model animal can contribute to the development of new therapeutic strategies toward various diseases involving neurological and vascular systems. Pterin derivatives other than biopterin may also be involved in the regulation of a variety of biological functions. We found that ciliated protozoan Tetrahymena pyriformis synthesizes tetrahydromonapterin, isomer of BH4, and its levels alter according to the progress of the cell cycle. How pterin derivatives are related to the human physiology and diseases is an interesting subject of investigation.

Tetrahydrobiopterin-deficient hyperphenylalaninemia in the Chinese

BACKGROUND

Hyperphenylalaninemia (HPA) may be caused by either a deficiency in phenylalanine-4-hydroxylase or in tetrahydrobiopterin (BH4), the essential cofactor required for the hydroxylation of aromatic amino acids. The most common forms of BH4 deficiency are 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency (MIM 261640) and dihydropteridine reductase (DHPR) deficiency (MIM 261630), which require a different treatment from classical HPA.

RESULTS

Approximately 86% of BH4-deficient HPA in the Chinese population was found to be caused by PTPS deficiency. Eleven missense (73C-->G, 120T-->G, 155A-->G, 166G-->A, 200C-->T, 209T-->A, 226C-->T, 259C-->T, 286G-->A, 317C-->T, 430G-->C), one splicing (IVS3+1G-->A) and two deletion mutations (116-119delTGTT, 169-171delGTG) were identified in 37 unrelated PTPS-deficient Chinese families. Among these, 155A-->G, 259C-->T and 286G-->A mutation accounted for about 80% of the mutant alleles. The 155A-->G and 286G-->A mutations were found to be the common mutation in southern and northern Chinese, respectively. Only two Chinese DHPR-deficient families were detected among about 300 Chinese hyperphenylalaninemia cases. A single base transition 508G-->A on the DHPR cDNA was identified in two consanguineous DHPR-deficient siblings. A reduced level of DHPR mRNA expression was found in the other DHPR-deficient patient, which suggested that the mutation might lie in the regulatory region of the DHPR gene.

CONCLUSIONS

The BH4-deficient HPA was estimated to make up around 30% of the Chinese population in Taiwan suffering from HPA, which is much higher than in Caucasian populations (1.5-2% of HPA).

Identification of mutations causing 6-pyruvoyl-tetrahydropterin synthase deficiency in four Italian families

6-Pyruvoyl-tetrahydrobiopterin synthase (PTPS) is involved in tetrahydrobiopterin (BH4) biosynthesis, the cofactor for various enzymes including the hepatic phenylalanine hydroxylase. Inherited PTPS deficiency leads to BH4 depletion, causes hyperphenylalaninemia, and requires cofactor replacement therapy for treatment. We previously isolated the human PTPS cDNA and recently characterized its corresponding gene, PTS. Here we developed PCR-based mutation analysis with newly designed primers to detect genomic alterations and describe five mutations, four of which are novel, in the PTS gene of four Italian families with affected individuals. The mutant alleles found included three missense mutations (T67M, K129E, D136V), a previously described triplet deletion (delta V57), and a single c-3-->g transversion in the 3'-acceptor splice site of intron 1, leading to cryptic splice site usage that resulted in a 12 bp deletion (mutant allele delta (K29-S32)). Except for K129E, all mutant alleles were inactive and/or unstable proteins, as shown by recombinant expression and Western blot analysis of patients' fibroblasts. The PTPS-deficient patient with the homozygous K129E allele had transient hyperphenylalaninemia, did not depend on BH4 replacement therapy, and showed normal PTPS immunoreactivity, but no enzyme activity in primary fibroblasts and red blood cells. In contrast to its inactivity in these cells, the K129E mutant was 2-3 fold more active than wild-type PTPS when transfected into COS-1 or the human hepatoma cell line Hep G2. K129E appears thus as a mutant PTPS whose activity depends on the cell type.

Reconstitution of a metabolic pathway with triple-cistronic IRES-containing retroviral vectors for correction of tetrahydrobiopterin deficiency

BACKGROUND

Tetrahydrobiopterin (BH4) is an essential cofactor for catecholamine and serotonin neurotransmitter biosynthesis. BH4 biosynthesis is carried out in a three-enzyme pathway involving GTP cyclohydrolase I (GTPCH), 6-pyruvoyl-tetrahydropterin synthase (PTPS) and sepiapterin reductase (SR). Treatment of genetic defects leading to BH4 deficiency requires neurotransmitter replacement since synthetic cofactor does not efficiently penetrate the blood-brain barrier. Autologous fibroblasts transplanted into the brain as depository cells for drug delivery might offer an alternative. However, normal fibroblasts do not express GTPCH, and fibroblasts from PTPS patients lack two biosynthetic enzymes for BH4 production.

METHODS

We engineered primary fibroblasts by the use of triple-cistronic, retroviral vectors for cofactor production.

RESULTS

Constitutive SR activity in these cells enabled BH4 biosynthesis by transducing GTPCH and PTPS cDNAs together with a selective marker coupled in a single transcript with two IRES-elements in tandem. Upon reaching a critical concentration (> 400 pmol/mg protein) of intracellular BH4, the fibroblasts efficiently released cofactor even under non-dividing conditions.

CONCLUSION

The use of triple-cistronic vectors for single transduction to reconstitute metabolic pathways or to treat multi-genetic diseases may be useful for engineering, for instance, depository cells for various organs, including the nervous system.

Isolated central form of tetrahydrobiopterin deficiency associated with hemizygosity on chromosome 11q and a mutant allele of PTPS

6-Pyruvoyl-tetrahydropterin synthase (PTS or PTPS) is involved in tetrahydrobiopterin (BH(4)) biosynthesis, the cofactor for various enzymes including the aromatic amino acid hydroxylases. Inherited PTPS deficiency is a heterogeneous disease with different phenotypes leading to BH(4) depletion. The severe form of PTPS deficiency causes hyperphenylalaninemia and monoamine neurotransmitter deficiency, whereas the mild form gives rise to hyperphenylalaninemia only. From 228 patients with PTPS deficiency at least 32 different mutant alleles have been identified on its corresponding gene, located on chromosome 11q22.3-q23.3. Here we describe a new allele from a child with PTPS deficiency who exhibited a mild but transient form of hyperphenylalaninemia, yet was deficient in CSF monoamines. The patient was found to carry, on her genomic DNA and cDNA, a homozygous A>G transition, leading to PTPS codon alteration Tyr99 to Cys (Y99C). The mother and several members of the maternal family were carriers of the Y99C allele, also verified by the reduced PTPS enzyme activity in erythrocytes. By cytogenetic, molecular, and FISH analyses, a de novo deletion spanning from 11q14 to 11q23.3 on the patient's paternal chromosome was mapped, establishing hemizygosity of the Y99C allele. The PTPS mutation observed in this patient generates a novel phenotype with an apparently isolated central form of BH(4) deficiency.

Single-Step Mutation Scanning of the 6-Pyruvoyltetrahydropterin Synthase Gene in Patients with Hyperphenylalaninemia

Background: Deficiency of 6-pyruvoyltetrahydropterin synthase (PTPS) is a recessively inherited disorder that leads to depletion of 5,6,7,8-tetrahydrobiopterin, the obligatory cofactor for hydroxylation of phenylalanine, tyrosine, and tryptophan. A marker for neonatal detection of PTPS deficiency is hyperphenylalaninemia (HPA). Molecular analysis would provide a simple and reliable means for distinguishing PTPS deficiency from other potential causes of HPA.

Methods: We developed a method based on PCR in combination with denaturing gradient gel electrophoresis (DGGE) that rapidly scans the six coding sequences and all splice sites of the PTPS gene (PTS) for mutations. This method was used to examine the status of the PTS gene in control samples with known PTS mutations and in five patients with PTPS deficiency.

Results: Two features of the PTS gene posed particular problems in relation to DGGE analysis: the very high GC content of exon 1, and a 15-bp poly(dT) stretch in the acceptor splice site of intron 1. Both problems were solved by special design of amplification primers. PCR and DGGE conditions were adjusted to allow simultaneous analysis of all six regions of the PTS gene. Using this one-step approach, all control mutations were readily resolved. Among the five PTPS patients, four mutations were identified, including IVS1-3C→G, IVS2-7T→A, V57del, and V97M (289G→A). The IVS1-3C→G mutation was shown by reverse transcription-PCR analysis to produce multiple splice variants.

Conclusions: We have established a fast and reliable screening method for detection of mutations and small deletions/insertions in the PTS gene. This method should be useful for rapid diagnosis of PTPS deficiency in newborns with HPA.

Structure, genomic localization and recombinant expression of the mouse 6-pyruvoyl-tetrahydropterin synthase gene

The 6-pyruvoyl-tetrahydropterin synthase (PTPS) is the second enzyme in the biosynthetic pathway from GTP to tetrahydrobiopterin (BH4). BH4 is an essential cofactor of NO synthases and aromatic amino acid hydroxylases, the latter being responsible for hepatic phenylalanine degradation and monoamine neurotransmitter biosynthesis. BH4 deficiency due to autosomal recessive mutations in the human gene for PTPS leads to a broad range of phenotypes ranging from mild hyperphenylalaninemia to high phenylalanine levels concomitant with neurotransmitter depletion. An animal model to study PTPS deficiency is thus desired to investigate the molecular basis of the disease and its variability. Here, we report on the isolation and recombinant expression of the mouse PTPS gene, Pts. It is located on chromosome 9C-D and contains six exons with an open reading frame of 144 codons. The derived protein monomer has a molecular mass of 16187 Da and shows 82% and 93% identity to its human and rat counterparts, respectively. The mouse PTPS was expressed in bacterial cells and purified to homogeneity. The kinetic properties of the recombinant protein, apparent Km of approximately 10 microM and k(cat) of 0.27 s(-1), were similar to the native mouse enzyme in liver and brain extracts, and to the corresponding human and rat PTPS.

Genomic organization and chromosomal localization of the human sepiapterin reductase gene

Sepiapterin reductase (SPR) catalyzes the final step of the biosynthetic pathway of tetrahydrobiopterin, which is an essential cofactor for aromatic amino acid hydroxylases and nitric oxide synthases. To aid the analysis of any possible human diseases caused by mutations in SPR, we have cloned and characterized the human SPR gene. The gene is composed of three exons spanning approximately 4 kilobases. The transcriptional starting point was determined around the cytosine nucleotide at position -81 by primer extension and RT-PCR analyses. There was no typical TATA-box within 300 bp from the transcriptional starting point. We found the Sp1-binding consensus sequence in the 5'-flanking region. The human SPR gene was mapped to chromosome band 2p13 by fluorescence in situ hybridization.

Mutation analysis of the 6-pyruvoyl-tetrahydropterin synthase gene in Chinese hyperphenylalaninemia caused by tetrahydrobiopterin synthesis deficiency

Hyperphenylalaninemia (HPA) may be caused by deficiency of phenylalanine hydroxylase or tetrahydrobiopterin (BH4), the essential cofactor for the aromatic amino acid hydroxylases. 6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is a major cause of BH4 deficient HPA. In this study, seven single base mutations at nucleotides 73 (C>G), 155 (A>G), 166 (G>A), 209 (T>A), 259 (C>T), 286 (G>A), and 317 (C>T) on PTPS cDNA were detected in Chinese PTPS-deficient HPA by polymerase chain reaction and solid phase DNA sequencing. These nucleotide alterations result in R25G, N52S, V56M, V70D, P87S, D96N, and T106M amino acid substitutions, respectively. The R25G, V56M, V70D, and T106M were novel mutations found in PTPS gene. By analysis of 38 PTPS mutant alleles from 19 unrelated Chinese PTPS-deficient HPA families, the allele frequency of these mutations in Chinese PTPS-deficient HPA were determined to be approximately 5.3% (R25G), 34.2% (N52S), 7.9% (V56M), 2.6% (V70D), 36.8% (P87S), 7.9% (D96N), and 2.6% (T106M), respectively. Two common mutations, N52S and P87S, were found to account for 71% of the Chinese PTPS mutant alleles. The N52S mutation accounts for 48% of the southern Chinese PTPS mutation, but only one (9%) of the northern Chinese PTPS mutant allele was found to be N52S, which suggested that the N52S mutation might be southern Chinese. Clinically, the V56M mutation was found to associate with the mild form of PTPS deficiency. However, the R25G, N52S, P87S, and D96N were found mainly in the patients with severe clinical symptom. Using polymerase chain reaction-based mutation analysis, a fetus at risk of PTPS deficiency was diagnosed prenatally to be a carrier of N52S mutation.

6-Pyruvoyl-tetrahydropterin synthase deficiency with generalized dystonia and diurnal fluctuation of symptoms: a clinical and molecular study

We report the case of a 44-year-old woman with a partial 6-pyruvoyl tetrahydropterin synthase (6-PTS) deficiency, whose predominant clinical symptom was generalized dystonia with marked diurnal fluctuation. Dystonia was present in the eyelids, oromandibular region, trunk, and extremities (Meige syndrome plus double hemiplegia-like dystonia). A marked and sustained positive response to levodopa was observed. A molecular genetic study revealed a homozygous mutation (I114V) in the 6-PTS gene. This study indicates that genetic abnormality in the 6-PTS gene may be a hereditary dystonia disorder. We speculate that our patient has residual 6-PTS activity in the central nervous system, such as in the liver, and we suggest that residual, but insufficient production of tetrahydrobiopterin may play an important role in causing diurnal fluctuation of symptoms.

Mutations in the GTP cyclohydrolase I and 6-pyruvoyl-tetrahydropterin synthase genes

Tetrahydrobiopterin deficiencies are highly heterogeneous disorders, with more than 30 molecular lesions identified in the past 2 years in the GTP cyclohydrolase I and 6-pyruvoyl-tetrahydropterin synthase genes. The spectrum of mutations causing a reduction of these two biosynthetic enzymes is reviewed. Only three mutations, two present homozygously, are reported in the GTP cyclohydrolase I gene to cause the rare autosomal recessively inherited form of hyperphenylalaninemia. Most of the other mutations, which are scattered over the entire coding region for the six exon-containing GTP cyclohydrolase I gene, are observed in a heterozygous state with the wild-type allele and are associated with the dominant DOPA-responsive dystonia. Compound heterozygous or homozygous mutations spread over all six exons encoding the 6-pyruvoyl-tetrahydropterin synthase cause an autosomal recessively inherited variant of hyperphenylalaninemia, mostly accompanied by a deficiency of dopamine and serotonin.