International database of tetrahydrobiopterin deficiencies

Crucial neuroprotective roles of the metabolite BH4 in dopaminergic neurons

Dopa-responsive dystonia (DRD) and Parkinson's disease (PD) are movement disorders caused by the dysfunction of nigrostriatal dopaminergic neurons. Identifying druggable pathways and biomarkers for guiding therapies is crucial due to the debilitating nature of these disorders. Recent genetic studies have identified variants of GTP cyclohydrolase-1 (GCH1), the rate-limiting enzyme in tetrahydrobiopterin (BH4) synthesis, as causative for these movement disorders. Here, we show that genetic and pharmacological inhibition of BH4 synthesis in mice and human midbrain-like organoids accurately recapitulates motor, behavioral and biochemical characteristics of these human diseases, with severity of the phenotype correlating with extent of BH4 deficiency. We also show that BH4 deficiency increases sensitivities to several PD-related stressors in mice and PD human cells, resulting in worse behavioral and physiological outcomes. Conversely, genetic and pharmacological augmentation of BH4 protects mice from genetically- and chemically induced PD-related stressors. Importantly, increasing BH4 levels also protects primary cells from PD-affected individuals and human midbrain-like organoids (hMLOs) from these stressors. Mechanistically, BH4 not only serves as an essential cofactor for dopamine synthesis, but also independently regulates tyrosine hydroxylase levels, protects against ferroptosis, scavenges mitochondrial ROS, maintains neuronal excitability and promotes mitochondrial ATP production, thereby enhancing mitochondrial fitness and cellular respiration in multiple preclinical PD animal models, human dopaminergic midbrain-like organoids and primary cells from PD-affected individuals. Our findings pinpoint the BH4 pathway as a key metabolic program at the intersection of multiple protective mechanisms for the health and function of midbrain dopaminergic neurons, identifying it as a potential therapeutic target for PD.

Phenotypes and Genotypes of Inherited Disorders of Biogenic Amine Neurotransmitter Metabolism

Inherited disorders of biogenic amine metabolism are genetically determined conditions resulting in dysfunctions or lack of enzymes involved in the synthesis, degradation, or transport of dopamine, serotonin, adrenaline/noradrenaline, and their metabolites or defects of their cofactor or chaperone biosynthesis. They represent a group of treatable diseases presenting with complex patterns of movement disorders (dystonia, oculogyric crises, severe/hypokinetic syndrome, myoclonic jerks, and tremors) associated with a delay in the emergence of postural reactions, global development delay, and autonomic dysregulation. The earlier the disease manifests, the more severe and widespread the impaired motor functions. Diagnosis mainly depends on measuring neurotransmitter metabolites in cerebrospinal fluid that may address the genetic confirmation. Correlations between the severity of phenotypes and genotypes may vary remarkably among the different diseases. Traditional pharmacological strategies are not disease-modifying in most cases. Gene therapy has provided promising results in patients with DYT-DDC and in vitro models of DYT/PARK-SLC6A3. The rarity of these diseases, combined with limited knowledge of their clinical, biochemical, and molecular genetic features, frequently leads to misdiagnosis or significant diagnostic delays. This review provides updates on these aspects with a final outlook on future perspectives.

Mutation spectrum of PTS gene in patients with tetrahydrobiopterin deficiency from jiangxi province

Background: Hyperphenylalaninemia (HPA) is the most common inborn error in amino acid metabolism. It can be primarily classified into phenylalanine hydroxylase (PAH) deficiency and tetrahydrobiopterin (BH4) deficiency. BH4 deficiency (BH4D) is caused by genetic defects in enzymes involved in the biosynthesis and regeneration of BH4. 6-pyruvoyl-tetrahydropterin synthase (PTPS/PTS), which is encoded by the PTS gene, participates in the biosynthesis of BH4. PTPS deficiency (PTPSD) is the major cause of BH4D. In this study, we investigated that the prevalence of BH4D in Jiangxi province was approximately 12.5 per 1,000,000 live births (69/5,541,627). Furthermore, the frequency of BH4D was estimated to be 28.8% (69/240) in the HPA population of Jiangxi. In this study, we aimed to characterize the mutational spectrum of the PTS gene in patients with PTPSD from Jiangxi province. Method: Newborn screening data of Jiangxi province from 1997 to 2021 were analyzed and 53 families with PTPSD were enrolled for the analysis of the PTS gene variants by Sanger sequencing. Results: 106 variants were identified in 106 alleles of 53 patients with PTPSD, including 13 types of variants reported previously, and two novel variants (c.164-36A>G and c.146_147insTG). The predominant variant was c.259C>T (47.2%), followed by c.84-291A>G (19.8%), c.155A>G (8.5%), c.286G>A (6.6%) and c.379C>T (4.7%). Conclusion: The results of this study can not only provide guidance for the molecular diagnosis and genetic counseling in cases of PTPS deficiency but also enrich the PTS mutation database.

Genotypic spectrum underlying tetrahydrobiopterin metabolism defects: Experience in a single Mexican reference center

Background: Pterin profiles or molecular analyses of hyperphenylalaninemia (HPA) caused by phenylalanine hydroxylase (PAH) deficiency or tetrahydrobiopterin deficiency (BH4D) are not always available in low- or middle-income countries, including Mexico, limiting information regarding the phenotypic and genotypic characteristics of patients exhibiting BH4D.

Objective: To report the genotypes underlying BH4D and the clinical presentation in unrelated Mexican HPA pediatric patients with normal PAH genotypes who attended a single metabolic reference center in Mexico.

Methods: Automated Sanger sequencing of the PTS, QDPR, and PCBD1 genes of 14 HPA patients was performed. Predicted effects on protein structure caused by missense variants were assessed by in silico protein modeling.

Results and discussion: A high prevalence of BH4D was noted in our HPA cohort (9.8%, N = 14/142). Clinically relevant biallelic genotypes were identified in the PTS (N = 7/14 patients), QDPR (N = 6/14 patients), and PCBD1 (N = 1/14 patients) genes. Four novel QDPR variants [c.714dup or p.(Leu239Thrfs*44), c.106-1G>T or p.(?), c.214G>T or p.(Gly72*), and c.187_189dup or p.(Gln63dup)] were identified. In silico protein modeling of six missense variants of PTS [p.(Thr67Met), p.(Glu81Ala), and p.(Tyr113Cys)], QDPR [p.(Cys161Phe) and p.(Pro172Leu)], and PCBD1 [p.(Glu97Lys)] supports their pathogenicity. Progressive neurological symptoms (mainly intellectual and motor impairment and even death in three patients) were noted in all patients with biallelic QDPR genotypes and in 5/7 patients bearing biallelic PTS genotypes. The single homozygous PCBD1 p.(Glu97Lys) patient remains asymptomatic.

Conclusion: A higher proportion of BH4D (9.8 vs. 1%–2% worldwide), attributable to a heterogeneous mutational spectrum and wide clinical presentation, was noted in our Mexican HPA cohort, with the PTS-related HPA disorder being the most frequent. Sequencing-based assays could be a reliable approach for diagnosing BH4D in our population.

Disorders of Tetrahydrobiopterin Metabolism: Experience from South India

BACKGROUND

Disorders of tetrahydrobiopterin metabolism represent a rare group of inherited neurotransmitter disorders that manifests mainly in infancy or childhood with developmental delay, neuroregression, epilepsy, movement disorders, and autonomic symptoms.

METHODOLOGY

A retrospective review of genetically confirmed cases of disorders of tetrahydrobiopterin metabolism over a period of three years (Jan 2018 to Jan 2021) was performed across two paediatric neurology centres from South India.

RESULTS

A total of nine patients(M:F=4:5) fulfilled the eligibility criteria. The genetic variants detected include homozygous mutations in the QDPR(n=6), GCH1(n=2), and PTS(n=1) genes. The median age at onset of symptoms was 6-months(range 3-78 months), while that at diagnosis was 15-months (8-120 months), resulting in a median delay in diagnosis of 9-months. The main clinical manifestations included neuroregression (89%), developmental delay(78%), dystonia(78%) and seizures(55%). Management strategies included a phenylalanine restricted diet, levodopa/carbidopa, 5-Hydroxytryphtophan, and folinic acid. Only, Patient-2 afforded and received BH4 supplementation at a sub-optimal dose later in the disease course. We had a median duration of follow up of 15 months (range 2-48 months). Though the biochemical response has been marked; except for patients with GTPCH deficiency, only mild clinical improvement was noted with regards to developmental milestones, seizures, or dystonia in others.

CONCLUSION

Tetrahydrobiopterin deficiencies represent a rare yet potentially treatable cause for non-phenylketonuria hyperphenylalaninemia with better outcomes when treated early in life. Screening for disorders of biopterin metabolism in patients with hyperphenylalaninemia prevents delayed diagnosis. This study expands the genotype-phenotype spectrum of patients with disorders of tetrahydrobiopterin metabolism from South India.

Insights into the expanding phenotypic spectrum of inherited disorders of biogenic amines

Inherited disorders of neurotransmitter metabolism are rare neurodevelopmental diseases presenting with movement disorders and global developmental delay. This study presents the results of the first standardized deep phenotyping approach and describes the clinical and biochemical presentation at disease onset as well as diagnostic approaches of 275 patients from the registry of the International Working Group on Neurotransmitter related Disorders. The results reveal an increased rate of prematurity, a high risk for being small for gestational age and for congenital microcephaly in some disorders. Age at diagnosis and the diagnostic delay are influenced by the diagnostic methods applied and by disease-specific symptoms. The timepoint of investigation was also a significant factor: delay to diagnosis has decreased in recent years, possibly due to novel diagnostic approaches or raised awareness. Although each disorder has a specific biochemical pattern, we observed confounding exceptions to the rule. The data provide comprehensive insights into the phenotypic spectrum of neurotransmitter disorders.

Inherited disorders of neurotransmitter metabolism represent a group of rare neurometabolic diseases characterized by movement disorders and developmental delay. Here, the authors report a standardized evaluation of a registry of 275 patients from 42 countries, and highlight an evolving phenotypic spectrum of this disease group and factors influencing diagnostic processes.

Birth prevalence of tetrahydrobiopterin deficiency in China: data from the national newborn screening program, 2013-2019

BACKGROUND

Tetrahydrobiopterin deficiency (BH4D), a less common form of hyperphenylalaninemia (HPA), can lead to severe developmental retardation if untreated. Little has been reported on the prevalence of BH4D among live births worldwide. This study examined its prevalence across China and between geographical areas within the country.

METHODS

We analyzed data from the Chinese national screening program for HPA in newborns between 2013 and 2019. BH4D prevalence was examined by province, region and the entire country. Provincial-level prevalence was estimated from the number of confirmed BH4D cases and screened newborns, after adjusting for HPA-positive recall rate. Regional- and national-level prevalences were estimated by summing provincial-level prevalences after weighting them by the number of live births. A Poisson distribution was assumed in order to calculate 95% confidence intervals (CIs) for prevalence.

RESULTS

Among 107,078,115 newborns screened for HPA in China, 380 with BH4D were identified, corresponding to a total prevalence of 3.8 per 1,000,000 live births. Prevalence was higher in eastern regions (5.9 per 1,000,000) and northern regions (4.1 per 1,000,000) of China than in southern regions (1.6 per 1,000,000) or northwestern regions (1.7 per 1,000,000). Across the entire country, 3.9% cases of HPA were diagnosed as BH4D, and this proportion reached as high as 15.1% in the southern part of the country.

CONCLUSIONS

These first insights into BH4D prevalence across China suggest slightly higher prevalence than in other countries, and it varies substantially by region. More attention should be paid to early diagnosis and timely treatment of BH4D.

[Newborn screening of phenylketonuria in France]

Phenylketonuria is the most common inborn error of metabolism and causes irreversible mental retardation if left untreated. Its newborn screening was made possible by the technique of blood collection on filter paper developed by Robert Guthrie. Neonatal PKU screening began in France in the early 1970s. It was initially carried out by a bacteriological method, then by fluorometry, and finally, since 2020, by tandem mass spectrometry. More than 35 million newborns have been screened to date. This resulted in the diagnosis of more than 3,500 children with PKU or mild hyperphenylalaninemia. The management of these children has improved over time, in particular thanks to the techniques of biochemistry and molecular genetics which lead to an accurate diagnosis and the arrival of drug treatment by sapropterin. Thanks to this screening, which allows for early management, the prognosis of PKU has been transformed and, although neurological or behavioral problems may arise, these patients are living normally today.

Tetrahydrobiopterin deficiencies: Lesson from clinical experience

OBJECTIVES

The present study describes clinical, biochemical, molecular genetic data, current treatment strategies and follow-up in nine patients with tetrahydrobiopterin (BH4) deficiency due to various inherited genetic defects.

METHODS

We analyzed clinical, biochemical, and molecular data of nine patients with suspected BH4 deficiency. All patients were diagnosed at Ege University Faculty of Medicine in Izmir, Turkey and comprised data collected from 2006 to 2019. The diagnostic laboratory examinations included blood phenylalanine and urinary or plasma pterins, dihydropteridine reductase (DHPR) enzyme activity measurement in dried blood spots, folic acid and monoamine neurotransmitter metabolites in cerebrospinal fluid, as well as DNA sequencing.

RESULTS

Among the nine patients, we identified one with autosomal recessive GTP cyclohydrolase I (ar GTPCH) deficiency, two with 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, three with sepiapterin reductase (SR) deficiency, and three with DHPR deficiency. Similar to previous observations, the most common clinical symptoms are developmental delay, intellectual disability, and movement disorders. All patients received treatment with l-dopa and 5-hydroxytryptophan, while only the ar GTPCH, the PTPS, and one DHPR deficient patients were supplemented in addition with BH4. The recommended dose range varies among patients and depends on the type of disease. The consequences of BH4 deficiencies are quite variable; however, early diagnosis and treatment will improve outcomes.

CONCLUSIONS

As BH4 deficiencies are rare group of treatable neurometabolic disorders, it is essential to diagnose the underlying (genetic) defect in newborns with hyperphenylalaninemia. Irreversible brain damage and progressive neurological deterioration may occur in untreated or late diagnosed patients. Prognosis could be satisfying in the cases with early diagnose and treatment.

Peripheral biopterin and neopterin in schizophrenia and depression

Increasing evidence points to a causal involvement of inflammation in the pathogenesis of neuropsychiatric disorders, including major depressive disorder (MDD) and schizophrenia (SZ). Neopterin and biopterin may link peripheral immune system activation and central neurotransmitter alterations. However, it is not fully established whether these alterations are transdiagnostic or disorder-specific and whether they are associated with reward-related psychopathologies. We investigated group differences in neopterin and biopterin in the plasma of healthy comparison (HC) (n=19), SZ (n=45) and MDD (n=43) participants. We then correlated plasma proteins with CRP as a measure for inflammation. Lastly, plasma proteins were correlated with the reward-related psychopathological domain apathy. We found a trend-level difference in biopterin levels and no significant difference in neopterin levels between groups. Within both patient groups, but not HC, we show a significant positive correlation of CRP with neopterin but not with biopterin. Further, we observed no significant correlations of plasma proteins with reward-related psychopathology in HC, MDD or SZ. While our study shows trend-level alterations of biopterin with relevance for future research, it does not support the hypothesis that peripheral neopterin or biopterin are associated with reward-related psychopathology.

Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH4) deficiencies

BACKGROUND

Tetrahydrobiopterin (BH4) deficiencies comprise a group of six rare neurometabolic disorders characterized by insufficient synthesis of the monoamine neurotransmitters dopamine and serotonin due to a disturbance of BH4 biosynthesis or recycling. Hyperphenylalaninemia (HPA) is the first diagnostic hallmark for most BH4 deficiencies, apart from autosomal dominant guanosine triphosphate cyclohydrolase I deficiency and sepiapterin reductase deficiency. Early supplementation of neurotransmitter precursors and where appropriate, treatment of HPA results in significant improvement of motor and cognitive function. Management approaches differ across the world and therefore these guidelines have been developed aiming to harmonize and optimize patient care. Representatives of the International Working Group on Neurotransmitter related Disorders (iNTD) developed the guidelines according to the SIGN (Scottish Intercollegiate Guidelines Network) methodology by evaluating all available evidence for the diagnosis and treatment of BH4 deficiencies.

CONCLUSION

Although the total body of evidence in the literature was mainly rated as low or very low, these consensus guidelines will help to harmonize clinical practice and to standardize and improve care for BH4 deficient patients.

Expanded Newborn Screening for Inborn Errors of Metabolism by Tandem Mass Spectrometry in Suzhou, China: Disease Spectrum, Prevalence, Genetic Characteristics in a Chinese Population

Expanded newborn screening for inborn errors of metabolism (IEMs) by tandem mass spectrometry (MS/MS) could simultaneously analyze more than 40 metabolites and identify about 50 kinds of IEMs. Next generation sequencing (NGS) targeting hundreds of IMEs-associated genes as a follow-up test in expanded newborn screening has been used for genetic analysis of patients. The spectrum, prevalence, and genetic characteristic of IEMs vary dramatically in different populations. To determine the spectrum, prevalence, and gene mutations of IEMs in newborns in Suzhou, China, 401,660 newborns were screened by MS/MS and 138 patients were referred to genetic analysis by NGS. The spectrum of 22 IEMs were observed in Suzhou population of newborns, and the overall incidence (excluding short chain acyl-CoA dehydrogenase deficiency (SCADD) and 3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD)) was 1/3,163. The prevalence of each IEM ranged from 1/401,660 to 1/19,128, while phenylketonuria (PKU) (1/19,128) and Mild hyperphenylalaninemia (M-HPA) (1/19,128) were the most common IEMs, followed by primary carnitine uptake defect (PCUD) (1/26,777), SCADD (1/28,690), hypermethioninemia (H-MET) (1/30,893), 3-MCCD (1/33,412) and methylmalonic acidemia (MMA) (1/40,166). Moreover, 89 reported mutations and 51 novel mutations in 25 IMEs-associated genes were detected in 138 patients with one of 22 IEMs. Some hotspot mutations were observed for ten IEMs, including PAH gene c.728G > A, c.611A > G, and c.721C > T for Phenylketonuria, PAH gene c.158G > A, c.1238G > C, c.728G > A, and c.1315+6T > A for M-HPA, SLC22A5 gene c.1400C > G, c.51C > G, and c.760C > T for PCUD, ACADS gene c.1031A > G, c.164C > T, and c.1130C > T for SCAD deficiency, MAT1A gene c.791G > A for H-MET, MCCC1 gene c.639+2T > A and c.863A > G for 3-MCCD, MMUT gene c.1663G > A for MMA, SLC25A13 gene c.IVS16ins3Kb and c.852_855delTATG for cittrullinemia II, PTS gene c.259C > T and c.166G > A for Tetrahydrobiopterin deficiency, and ACAD8 gene c.1000C > T and c.286C > A for Isobutyryl coa dehydrogenase deficiency. All these hotspot mutations were reported to be pathogenic or likely pathogenic, except a novel mutation of ACAD8 gene c.286C > A. These mutational hotspots could be potential candidates for gene screening and these novel mutations expanded the mutational spectrum of IEMs. Therefore, our findings could be of value for genetic counseling and genetic diagnosis of IEMs.

Gene mutation and pedigree analysis of tetrahydrobiopterin deficiency in a Uygur family of China

BACKGROUND

Tetrahydrobiopterin (BH4 ) deficiency is an autosomal recessive disorder, which is caused by an enzyme deficiency involved in its synthetic or metabolic pathways. Clinical symptoms may include microcephaly, hypoevolutism, severe ataxia, and seizures. The purposes of this study are to analyze the genotype-phenotype and the pedigree of the first case of BH4 deficiency in the Uygur of China.

METHODS

(a) This patient received tandem mass spectrometry, urinary neopterin and biopterin analysis, and determination of dihydropteridine reductase (DHPR) activity in dried blood spots. (b) Blood DNA samples of this patient and her three family members were collected for gene sequencing and mutation analysis.

RESULTS

(a) The basic urinary neopterin and biopterin were 1.07 mmol/mol Cr and 3.12 mmol/mol Cr, respectively, and biopterin percentage was 74.42%. The DHPR activity of this patient was 31.11% of normal control. (b) Sanger sequencing of PAH gene in this patient was negative but positive of her sister, which carries 2 heterozygous mutation c.781C>T and c.1238G>C. Next-generation sequencing on the patient identified a homozygous mutation in the quinoid dihydropteridine reductase (QDPR) gene at c.508G>A, which was confirmed by Sanger sequencing.

CONCLUSION

(a) The patient was the first case of clinical diagnosis of BH4 deficiency in the Uighur. And there are two types of hyperphenylalaninemia (HPA) in the same family. (b) The mild HPA patient with severe nervous system damage should pay more attention to the BH4 deficiency. (c) Using next-generation sequencing technology can increase the mutation detection rate when the hereditary diseases are highly suspected in clinic.

Molecular genetics of tetrahydrobiopterin deficiency in Chinese patients

Background The overall incidence of hyperphenylalaninemia (HPA) in China is 1:11,763, with tetrahydrobiopterin (BH4) deficiency accounting for 8.55% of patients with HPA in the mainland. Much progress has been made in the diagnosis and treatment of BH4 deficiency with the introduction of neonatal screening in China. However, the screening rate is still low and screening is not universally available. Methods A total of 44 BH4-deficient patients were enrolled in this study, of which 39 were diagnosed with BH4 deficiency, while the remaining five showed typical characteristics of BH4 deficiency at a later period. The entire coding regions and adjacent intronic regions of GCH1, PTS, PCBD1 and QDPR genes were analyzed using target sequencing. Results Nineteen (n=19) different mutations in the PTS gene including four novel mutations and one mutation in QDPR were identified. p.P87S, p.D96N, IVS1-291A>G, p.N52S, p.K91R, p.V56M, p.T106M and p.F40GfsX53 in PTS were the prevalent mutations with ≥3% relative frequency. The mutation p.R221X in the QDPR gene was found with relatively lower frequencies (2.27%). The remaining 12 mutations in PTS were found at relative frequencies of 1.14%. Conclusions The results could be of value for genetic counseling and prenatal diagnosis in the patients' families and for the molecular diagnosis of BH4 deficiencies. Furthermore, four novel mutations expand and improve the PTS mutation database.

Efficacy, safety and population pharmacokinetics of sapropterin in PKU patients <4 years: results from the SPARK open-label, multicentre, randomized phase IIIb trial

BACKGROUND

Sapropterin dihydrochloride, a synthetic formulation of BH4, the cofactor for phenylalanine hydroxylase (PAH, EC 1.14.16.1), was initially approved in Europe only for patients ≥4 years with BH4-responsive phenylketonuria. The aim of the SPARK (Safety Paediatric efficAcy phaRmacokinetic with Kuvan®) trial was to assess the efficacy (improvement in daily phenylalanine tolerance, neuromotor development and growth parameters), safety and pharmacokinetics of sapropterin dihydrochloride in children <4 years.

RESULTS

In total, 109 male or female children <4 years with confirmed BH4-responsive phenylketonuria or mild hyperphenylalaninemia and good adherence to dietary treatment were screened. 56 patients were randomly assigned (1:1) to 10 mg/kg/day oral sapropterin plus a phenylalanine-restricted diet or to only a phenylalanine-restricted diet for 26 weeks (27 to the sapropterin and diet group and 29 to the diet-only group; intention-to-treat population). Of these, 52 patients with ≥1 pharmacokinetic sample were included in the pharmacokinetic analysis, and 54 patients were included in the safety analysis. At week 26 in the sapropterin plus diet group, mean phenylalanine tolerance was 30.5 (95% confidence interval 18.7-42.3) mg/kg/day higher than in the diet-only group (p < 0.001). The safety profile of sapropterin, measured monthly, was acceptable and consistent with that seen in studies of older children. Using non-linear mixed effect modelling, a one-compartment model with flip-flop pharmacokinetic behaviour, in which the effect of weight was substantial, best described the pharmacokinetic profile. Patients in both groups had normal neuromotor development and stable growth parameters.

CONCLUSIONS

The addition of sapropterin to a phenylalanine-restricted diet was well tolerated and led to a significant improvement in phenylalanine tolerance in children <4 years with BH4-responsive phenylketonuria or mild hyperphenylalaninemia. The pharmacokinetic model favours once per day dosing with adjustment for weight. Based on the SPARK trial results, sapropterin has received EU approval to treat patients <4 years with BH4-responsive phenylketonuria.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01376908 . Registered June 17, 2011.

Neopterin as a potential cytoprotective brain molecule

Neopterin, a byproduct of the tetrahydrobiopterin de novo pathway, is found in increased levels in cerebrospinal fluid and plasma and significantly increases upon damage, infection or during immune system activation. The production of this compound seems almost restricted to the monocyte/macrophage linage cells, in response to interferon-γ stimulation. However, it is unclear whether and which nervous cells are able to synthesize neopterin, respond to any stressor applied extracellularly, or even the role of the compound in the central nervous system. Here we propose a potential cytoprotective role of neopterin in the brain, and show evidence that cultured rat astrocytes are responsive to the molecule; the pterin elicited increased hemeoxygenase-1 cellular content and decreased oxidative stress induced by mitochondrial dysfunction. Further studies are needed to clarify neopterin's cytoprotective effects in the central nervous system, and its potential role in different neuroinflammatory diseases.

Molecular and enzymatic characterization of two enzymes BmPCD and BmDHPR involving in the regeneration pathway of tetrahydrobiopterin from the silkworm Bombyx mori

Tetrahydrobiopterin (BH4) is an essential cofactor of aromatic amino acid hydroxylases and nitric oxide synthase so that BH4 plays a key role in many biological processes. BH4 deficiency is associated with numerous metabolic syndromes and neuropsychological disorders. BH4 concentration in mammals is maintained through a de novo synthesis pathway and a regeneration pathway. Previous studies showed that the de novo pathway of BH4 is similar between insects and mammals. However, knowledge about the regeneration pathway of BH4 (RPB) is very limited in insects. Several mutants in the silkworm Bombyx mori have been approved to be associated with BH4 deficiency, which are good models to research on the RPB in insects. In this study, homologous genes encoding two enzymes, pterin-4a-carbinolamine dehydratase (PCD) and dihydropteridine reductase (DHPR) involving in RPB have been cloned and identified from B. mori. Enzymatic activity of DHPR was found in the fat body of wild type silkworm larvae. Together with the transcription profiles, it was indicated that BmPcd and BmDhpr might normally act in the RPB of B. mori and the expression of BmDhpr was activated in the brain and sexual glands while BmPcd was expressed in a wider special pattern when the de novo pathway of BH4 was lacked in lemon. Biochemical analyses showed that the recombinant BmDHPR exhibited high enzymatic activity and more suitable parameters to the coenzyme of NADH in vitro. The results in this report give new information about the RPB in B. mori and help in better understanding insect BH4 biosynthetic networks.

Functional analysis of sepiapterin reductase in Drosophila melanogaster

Sepiapterin reductase (SR) is a key enzyme involved in the biosynthesis of tetrahydrobiopterin (BH4), an essential cofactor for the synthesis of important biogenic amines, including catecholamines and serotonin. BH4 deficiencies have been implicated in several neurological disorders. Here, we characterized sepiapterin reductase (SR) loss-of-function mutants in Drosophila melanogaster and demonstrated that SR mutations are responsible for hyposensitivity to oxidative stress. Biochemical analysis further revealed that SR activity and BH4 levels in SR mutants were significantly reduced. Furthermore, we showed that the levels of phosphorylated Akt and total Akt protein were increased in SR mutants. Our findings indicate that SR plays an important role in the Akt pathway and that SR mutants will be a valuable tool for investigating the physiological functions of BH4.

The Kuvan(®) Adult Maternal Paediatric European Registry (KAMPER) Multinational Observational Study: Baseline and 1-Year Data in Phenylketonuria Patients Responsive to Sapropterin

INTRODUCTION

Sapropterin dihydrochloride (Kuvan(®)), a synthetic 6R-diastereoisomer of tetrahydrobiopterin (BH4), is approved in Europe for the treatment of patients aged ≥4 years with hyperphenylalaninaemia (HPA) due to BH4-responsive phenylalanine hydroxylase (PAH) deficiency, in conjunction with a phenylalanine-restricted diet, and also for the treatment of patients with BH4 deficiency.

AIMS/METHODS

KAMPER is an ongoing, observational, multicentre registry with the primary objective of providing information over 15 years on long-term safety of sapropterin dihydrochloride treatment in patients with HPA. Here we report initial data on characteristics from patients recruited by the time of the third interim analysis and results at 1 year.

RESULTS

Overall, 325 patients from 55 sites in seven European countries were included in the analysis: 296 (91.1%) patients with PAH deficiency (median [Q1, Q3] age, 10.3 [7.2, 15.0] years) and 29 (8.9%) with BH4 deficiency (12.8 [6.6, 18.9] years). Fifty-nine patients (18.2%) were aged ≥18 years; 4 patients were pregnant. No elderly patients (aged ≥65 years) or patients with renal or hepatic insufficiency were enroled in the study. Twelve-month data were available for 164 patients with PAH deficiency and 16 with BH4 deficiency. No new safety concerns were identified as of May 2013.

CONCLUSIONS

Initial data from KAMPER show that sapropterin dihydrochloride has a favourable safety profile. Registry data collected over time will provide insight into the management and outcomes of patients with PAH deficiency and BH4 deficiency, including long-term safety, impact on growth and neurocognitive outcomes and the effect of sapropterin dihydrochloride treatment on populations of special interest.

Mutations in PCBD1 cause hypomagnesemia and renal magnesium wasting

Mutations in PCBD1 are causative for transient neonatal hyperphenylalaninemia and primapterinuria (HPABH4D). Until now, HPABH4D has been regarded as a transient and benign neonatal syndrome without complications in adulthood. In our study of three adult patients with homozygous mutations in the PCBD1 gene, two patients were diagnosed with hypomagnesemia and renal Mg(2+) loss, and two patients developed diabetes with characteristics of maturity onset diabetes of the young (MODY), regardless of serum Mg(2+) levels. Our results suggest that these clinical findings are related to the function of PCBD1 as a dimerization cofactor for the transcription factor HNF1B. Mutations in the HNF1B gene have been shown to cause renal malformations, hypomagnesemia, and MODY. Gene expression studies combined with immunohistochemical analysis in the kidney showed that Pcbd1 is expressed in the distal convoluted tubule (DCT), where Pcbd1 transcript levels are upregulated by a low Mg(2+)-containing diet. Overexpression in a human kidney cell line showed that wild-type PCBD1 binds HNF1B to costimulate the FXYD2 promoter, the activity of which is instrumental in Mg(2+) reabsorption in the DCT. Of seven PCBD1 mutations previously reported in HPABH4D patients, five mutations caused proteolytic instability, leading to reduced FXYD2 promoter activity. Furthermore, cytosolic localization of PCBD1 increased when coexpressed with HNF1B mutants. Overall, our findings establish PCBD1 as a coactivator of the HNF1B-mediated transcription necessary for fine tuning FXYD2 transcription in the DCT and suggest that patients with HPABH4D should be monitored for previously unrecognized late complications, such as hypomagnesemia and MODY diabetes.

Demographics, diagnosis and treatment of 256 patients with tetrahydrobiopterin deficiency in mainland China: results of a retrospective, multicentre study

BACKGROUND

National coverage of neonatal screening for hyperphenylalaninaemia (HPA) in China is still low and tests to differentiate causes of HPA are not performed in many centres. This study aimed to describe the demographics, geographic distribution, diagnosis, treatment and clinical outcomes of treatment, including intellectual development, in patients with tetrahydrobiopterin (BH4) deficiency in mainland China.

METHODS

This was a retrospective, multicentre, chart review in patients with BH4 deficiency across mainland China born 1985-2010.

RESULTS

Two hundred fifty six patients were included; 59.9 % (267/446) of parents were from eastern China. Median (interquartile range) age at diagnosis decreased from 12.0 (5.5, 102.0) months to 2.0 (1.0, 3.5) months in patients born 1985-1999 (n = 28) and 2005-2010 (n = 152), respectively. 6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency was the primary cause of BH4 deficiency (96.0 %); four hotspot mutations accounted for 76.6 % of PTS gene mutations; two novel variants in the QDPR gene were identified. Most patients (83.6 %) received treatment with BH4, L-dopa, 5-hydroxytryptophan and/or diet therapy. Target blood Phe concentration was confirmed at 88.9 % of visits; median (Q1, Q3) blood Phe concentration was 106.8 (73.0, 120.0) μmol/L during therapy and 117.0 (67.1, 120.0) μmol/L at last visit. Median (Q1, Q3) WISC IQ score was 80.0 (69.0, 90.0) in 33 patients. DQ scores were within normal range (≥85) for 37/59 (62.7 %) patients. Physical development indicators were within normal ranges. Treatment-related adverse events, reported in 20/256 (7.8 %) patients, were mild-to-moderate in severity.

CONCLUSION

This study provides valuable information on the current and historical situation of BH4 deficiency in mainland China.

Dihydropteridine reductase deficiency and treatment with tetrahydrobiopterin: a case report

Dihydropteridine reductase (DHPR) deficiency is a genetic disorder of tetrahydrobiopterin (BH4) regeneration and may present with hyperphenylalaninemia, microcephaly, hypotonia, mental retardation, and convulsions. BH4 is an essential cofactor for the hydroxylation of aromatic amino acids and a deficiency of BH4 results in decreased synthesis of dopamine and serotonin. We present a 27-month-old female patient with DHPR deficiency who was treated with L-dopa/carbidopa (2 mg/kg, four times per day), 5-hydroxytryptophan (2 mg/kg, four times per day), folinic acid (10 mg/day), and BH4 supplementation (20 mg/kg, twice a day). Although remarkable clinical improvement with normal plasma phenylalanine (Phe) levels and increased phenylalanine tolerance was noted 1 month after the treatment, CSF neurotransmitter metabolites did not improve. BH4 supplementation was increased to 40 mg/kg/day and the CSF study was repeated 1 month later. There was no significant change of CSF neurotransmitters, BH4 or BH2 levels but plasma Phe level was within normal range. Surprisingly, she had developmental improvement noted at 1-month and 3-month visits following an augmented neurotransmitter and BH4 treatment. She was able to pull herself to the standing position and sit down on her own. She was also noted to be more alert and responsive following treatment. Her expressive language did not improve, although her receptive language was markedly improved. The above treatment improved patient's clinical findings, normalized blood Phe levels, and increased Phe tolerance in the diet, but neither 20 nor 40 mg/kg/day BH4 supplementation corrected neurotransmitter or BH4 levels or increased BH2 level in CSF. Further studies are needed to find the optimal management plan for patients with DHPR deficiency.

An international survey of patients with tetrahydrobiopterin deficiencies presenting with hyperphenylalaninaemia

OBJECTIVES

The present study summarizes clinical and biochemical findings, current treatment strategies and follow-up in patients with tetrahydrobiopterin (BH(4)) deficiencies.

METHODS

We analyzed the clinical, biochemical and treatment data of 626 patients with BH(4) deficiencies [355 with 6-pyruvoyl-tetrahydropterin synthase (PTPS), 217 with dihydropteridine reductase (DHPR), 31 with autosomal recessive GTP cyclohydrolase I (GTPCH), and 23 with pterin-4a-carbinolamine dehydratase (PCD) deficiencies] from the BIODEF Database. Patients with autosomal dominant GTPCH and SR deficiencies will not be discussed in detail.

RESULTS

Up to 57 % of neonates with BH(4) deficiencies are already clinically symptomatic. During infancy and childhood, the predominant symptoms are muscular hypotonia, mental retardation and age-dependent movement disorders, including dystonia. The laboratory diagnosis of BH(4) deficiency is based on a positive newborn screening (NBS) for phenylketonuria (PKU), characteristic profiles of urinary or dried blood spot pterins (biopterin, neopterin, and primapterin), and the measurement of DHPR activity in blood. Some patients with autosomal recessive GTPCH deficiency and all with sepiapterin reductase deficiency may be diagnosed late due to normal blood phenylalanine in NBS. L-dopa, 5-hydroxytryptophan, and BH(4) are supplemented in PTPS and GTPCH-deficient patients, whereas L-dopa, 5-hydroxytryptophan, folinic acid and diet are used in DHPR-deficient patients. Medication doses vary widely among patients, and our understanding of the effects of dopamine agonists and monoamine catabolism inhibitors are limited.

CONCLUSIONS

BH(4) deficiencies are a group of treatable pediatric neurotransmitter disorders that are characterized by motor dysfunction, mental retardation, impaired muscle tone, movement disorders and epileptic seizures. Although the outcomes of BH(4) deficiencies are highly variable, early diagnosis and treatment result in improved outcomes.

Infantile spasms (West syndrome) in children with inborn errors of metabolism: a review of the literature

West syndrome (infantile spasms) is an epileptic encephalopathy that includes psychomotor deterioration. In rare cases, it is due to an inherited, progressive metabolic disease. More than 25 inborn errors of metabolism have been considered etiologic or predisposing factors for infantile spasms. This is a review of the literature on reported cases of children diagnosed with a metabolic disease who developed infantile spasms. This article presents in brief the most frequent inborn errors of metabolism that have been associated with West syndrome and also illustrates the importance of screening for inborn errors of metabolism in infantile spasms.

GCH1, BH4 and pain

Understanding and consequently treating neuropathic pain effectively is a challenge for modern medicine, as unlike inflammation, which can be controlled relatively well, chronic pain due to nerve injury is refractory to most current therapeutics. Here we define a target pathway for a new class of analgesics, tetrahydrobiopterin (BH4) synthesis and metabolism. BH4 is an essential co-factor in the synthesis of serotonin, dopamine, epinephrine, norepinephrine and nitric oxide and as a result, its availability influences many systems, including neurons. Following peripheral nerve damage, levels of BH4 are dramatically increased in sensory neurons, consequently this has a profound effect on the physiology of these cells, causing increased activity and pain hypersensitivity. These changes are principally due to the upregulation of the rate limiting enzyme for BH4 synthesis GTP Cyclohydrolase 1 (GCH1). A GCH1 pain-protective haplotype which decreases pain levels in a variety of settings, by reducing the levels of endogenous activation of this enzyme, has been characterized in humans. Here we define the control of BH4 homeostasis and discuss the consequences of large perturbations within this system, both negatively via genetic mutations and after pathological increases in the production of this cofactor that result in chronic pain. We explain the nature of the GCH1 reduced-function haplotype and set out the potential for a ' BH4 blocking' drug as a novel analgesic.

Whole-genome sequencing for optimized patient management

Whole-genome sequencing of patient DNA can facilitate diagnosis of a disease, but its potential for guiding treatment has been under-realized. We interrogated the complete genome sequences of a 14-year-old fraternal twin pair diagnosed with dopa (3,4-dihydroxyphenylalanine)-responsive dystonia (DRD; Mendelian Inheritance in Man #128230). DRD is a genetically heterogeneous and clinically complex movement disorder that is usually treated with l-dopa, a precursor of the neurotransmitter dopamine. Whole-genome sequencing identified compound heterozygous mutations in the SPR gene encoding sepiapterin reductase. Disruption of SPR causes a decrease in tetrahydrobiopterin, a cofactor required for the hydroxylase enzymes that synthesize the neurotransmitters dopamine and serotonin. Supplementation of l-dopa therapy with 5-hydroxytryptophan, a serotonin precursor, resulted in clinical improvements in both twins.

GTP-cyclohydrolase deficiency responsive to sapropterin and 5-HTP supplementation: relief of treatment-refractory depression and suicidal behaviour

The authors describe a new variant of guanosine triphosphate (GTP)- cyclohydrolase deficiency in a young man with severe and disabling major depressive disorder with multiple near-lethal suicide attempts. His cerebrospinal fluid levels showed that the concentration of tetrahydrobiopterin (BH4), neopterin, 5-hydroxyindoleacetic acid and homovanillic acid were below the reference range, suggesting a defect in the pterin biosynthetic pathway and in synthesis of dopamine and serotonin indicative of GTP-cyclohydrolase deficiency. Patient was started on sapropterin, a BH4 replacement protein, for the defect in the above pathway. In addition, the authors started 5-hydroxytryptophan titrated to 400 mg orally twice daily with concomittant carbidopa 37.5 mg orally four times a day, and he responded with remission of suicidal ideation and significant improvement in depression and function.

Dopa-responsive dystonia

Clinical characteristics and pahophysiologies of dopa-responsive dystonia are discussed by reviewing autosomal-dominant GTP cyclohydrolase-I deficiency (AD GCHI D), recessive deficiencies of enzymes of pteridine metabolism, and recessive tyrosine hydroxylase (TH). Pteridine and TH metabolism involve TH activities in the terminals of the nigrostriatal dopamine neuron which show high in early childhood and decrease exponentially with age, attaining stational low levels by the early 20s. In these disorders, TH in the terminals follows this course with low levels and develops particular symptoms with functional maturation of the downstream structures of the basal ganglia; postural dystonia through the direct pathway and descending output matured earlier in early childhood and parkinsonism in TH deficiency in teens through the D2 indirect pathway ascending output matured later. In action-type AD GCHI D, deficiency of TH in the terminal on the subthalamic nucleus develops action dystonia through the descending output in childhood, focal and segmental dystonia and parkinsonism in adolescence and adulthood through the ascending pathway maturing later. Dysfunction of dopamine in the terminals does not cause degenerative changes or higher cortical dysfunction. In recessive disorders, hypofunction of serotonin and noradrenaline induces hypofunction of the dopamine in the perikaryon and shows cortical dysfunction.

Tetrahydrobiopterin in the prevention of hypertonia in hypoxic fetal brain

OBJECTIVE

Tetrahydrobiopterin (BH(4)) deficiency is a cause of dystonia at birth. We hypothesized that BH(4) is a developmental factor determining vulnerability of the immature fetal brain to hypoxic-ischemic injury and subsequent motor deficits in newborns.

METHODS

Pregnant rabbits were subjected to 40-minute uterine ischemia, and fetal brains were investigated for global and focal changes in BH(4). Newborn kits were assessed by neurobehavioral tests following vehicle and sepiapterin (BH(4) analog) treatment of dams.

RESULTS

Naive fetal brains at 70% gestation (E22) were severely deficient for BH(4) compared with maternal and other fetal tissues. BH(4) concentration rapidly increased normally in the perinatal period, with the highest concentrations found in the thalamus compared with basal ganglia, frontal, occipital, hippocampus, and parietal cortex. Global sustained 40-minute hypoxia-ischemia depleted BH(4) in E22 thalamus and to a lesser extent in basal ganglia, but not in the frontal, occipital, and parietal regions. Maternal supplementation prior to hypoxia-ischemia with sepiapterin increased BH(4) in all brain regions and especially in the thalamus, but did not increase the intermediary metabolite, 7,8-BH(2). Sepiapterin treatment also reduced incidence of severe motor deficits and perinatal death following E22 hypoxia-ischemia.

INTERPRETATION

We conclude that early developmental BH(4) deficiency plays a critical role in hypoxic-ischemic brain injury. Increasing brain BH(4) via maternal supplementation may be an effective strategy in preventing motor deficits from antenatal hypoxia-ischemia.

The silkworm mutant lemon (lemon lethal) is a potential insect model for human sepiapterin reductase deficiency

Tetrahydrobiopterin (BH4) is an essential cofactor for aromatic acid hydroxylases, which control the levels of monoamine neurotransmitters. BH4 deficiency has been associated with many neuropsychological disorders. An inherited defect in BH4 biosynthesis is caused by the deficiency of sepiapterin reductase (SPR), which catalyzes the biosynthesis of BH4 from guanosine triphosphate at the terminal step. The human SPR gene has been mapped at the PARK3 locus, which is related to the onset of Parkinson disease. In this study, we report that mutant strains, lemon (lem) and its lethal allele lemon lethal (lem(1)) with yellow body coloration, of the silkworm Bombyx mori could be used as the first insect model for human SPR deficiency diseases. We demonstrated that mutations in the SPR gene (BmSpr) were responsible for the irregular body coloration of lem and lem(l). Moreover, biochemical analysis revealed that SPR activity in lem(l) larvae was almost completely diminished, resulting in a lethal phenotype that the larvae cannot feed and that die immediately after the first ecdysis. Oral administration of BH4 and dopamine to lem(l) larvae effectively increased their survival rates and feeding abilities. Our data demonstrate that BmSPR plays a crucial role in the generation of BH4, and monoamine neurotransmitters in silkworms and the lem (lem(l)) mutant strains will be an invaluable resource to address many questions regarding SPR and BH4 deficiencies.

Phenotypic variability, neurological outcome and genetics background of 6-pyruvoyl-tetrahydropterin synthase deficiency

This study aimed to investigate the clinical variability and factors implied in the outcome of 6-pyruvoyl-tetrahydropterin synthase deficiency (PTPSd). Biochemical and clinical phenotype, treatment variables, and 6-pyruvoyl-tetrahydropterin synthase (PTS) genotype, were explored retrospectively in 19 Italian patients (12 males and 7 females, aged 4 months to 33 years). According to the level of biogenic amines in cerebrospinal fluid (CSF) at the diagnosis, the patients were classified as mild (6) (normal level) or severe (13) (abnormal low level) form (MF and SF, respectively). Blood Phe ranged from 151 to 1053 micromol/l in MF (mean +/- SD: 698 +/- 403) and 342-2120 micromol/l in SF (mean +/- SD: 1175 +/- 517) (p = 0.063). Patients with MF showed a normal neurological development (a transient dystonia was detected in one), while all SF patients except one presented with severe neurological impairment and only four had a normal neurological development. The outcome of the SF was influenced by the precocity of the treatment. Serial CSF examinations revealed a decline of 5-hydroxyindolacetic acid in MFs and an incomplete restoration of neurotransmitters in SFs: neither obviously affected the prognosis. PTS gene analysis detected 17 different mutations (seven so far unreported) (only one affected allele was identified in three subjects). A good correlation was found between genotype and clinical and biochemical phenotype. The occurrence of brain neurotransmitter deficiency and its early correction (by the therapy) are the main prognostic factors in PTPSd.

Evaluation of neonatal BH4 loading test in neonates screened for hyperphenylalaninemia

BACKGROUND

The outcome in phenylketonuria is related to the early diagnosis and management due to neonatal screening.

AIMS

To assess the interest of tetrahydrobiopterin (BH4) loading test and phenylalanine hydroxylase (PAH) genotyping in the management of neonates with hyperphenylalaninemia (HPA).

STUDY DESIGN

We evaluate the effectiveness of a BH4 loading test (20 mg/kg) in ten neonates screened for HPA. We evaluated the time required to reach a target plasma Phenylalanine (Phe) level below 300 micromol/l. We compared these ten BH4-loaded patients to the 10 previous neonates non-loaded with BH4. In all these patients, the PAH genotype was determined.

RESULTS

One loaded patient had biopterin synthesis deficiency and has been retrieved from statistical analysis. All others patients have PAH deficiency. Between the BH4 loaded group (L) and the BH4 non-loaded group (NL), a statistically significant difference was observed in the average time required to reached the target Phe level (13.56 +/- 4.30 (L) vs. 20.6 +/- 7.59 days (NL) [p < 0.02]). Results of the genotyping from all but one of these 19 patients indicated that among all mutations present in this patient population, there were 4 known PAH mutations associated with BH4 responsiveness (p.R261Q, the p.V388 M, the p.E390G and the p.Y414C). These mutations were found in 4 non-loaded and 6 loaded patients. Two patients had a more than 90% reduction in their plasma Phe level within 24 h after the load. One of these patients had a PTPS deficiency. The other fully responsive patient (p.Y414C and IVS10-11G>A) has been treated with BH4 from birth with an excellent metabolic control for three years now.

CONCLUSION

BH4 loading test improves the management of HPA. It allows an immediate identification of the children fully responsive to BH4. Our results therefore suggest the incorporation of BH4 loading test in the management of neonates screened for HPA.

Outcome and long-term follow-up of 36 patients with tetrahydrobiopterin deficiency

We describe the treatment, the clinical, and biochemical findings and the outcome of 26 patients with 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency and 10 patients with dihydropteridine reductase (DHPR) deficiency. These are the two most common forms of the autosomal-recessively inherited tetrahydrobiopterin (BH4) deficiency. Time of diagnosis, dosage of BH4 and neurotransmitter precursors, folinic acid substitution, and levels of 5-hydroxyindoleacetic acid (5HIAA) and homovanillic acid (HVA) in cerebrospinal fluid (CSF) are essential parameters in the follow-up of patients. Unfortunately, treatment protocols vary greatly among patients and clinical centers, and CSF investigations and outcome assessments are not always available. Seventeen patients with PTPS deficiency and four patients with DHPR deficiency were diagnosed within 2 months after birth. In 14 patients with PTPS deficiency (54%; 9 early and 5 late diagnosed) and 2 patients with DHPR deficiency (20%; all early diagnosed) no developmental delay is observed, while in 10 patients with PTPS deficiency (38%; 6 early and 4 late diagnosed) and 8 patients with DHPR deficiency (80%; 2 early and 6 late diagnosed) development was delayed. Two PTPS-deficient patients died in the newborn period. DHPR deficiency seems to be more severe than PTPS deficiency and it is clearly the onset of treatment that determines the outcome. Our data suggest that diagnosis within the first month of life is essential for a good outcome and that low CSF5 HIAA and HVA values in CSF could be an indicator for the ongoing developmental impairment

Early initiation of L-dopa therapy enables stable development of executive function in tetrahydrobiopterin (BH4) deficiency

Executive function (EF) has been presumed to be mediated by the dopaminergic system in the prefrontal cortex. However, little is known about the early development of this function and the roles dopamine plays in it. Tetrahydrobiopterin (BH4) deficiencies are genetic disorders affecting catecholamine and serotonin biosynthesis which, if untreated, result in motor and cognitive symptoms including impairment of EF. A comprehensive neuropsychological test battery was administered to six participants with BH4 deficiency (four males, two females, mean Full-scale intelligence quotient [FIQ] 63.8 [SD 14.7]); all were on replacement therapy with L-dopa and BH4, but time of initiation of treatment varied. Age range (median) was 28 days to 41 years (2y 6mo) at initiation of treatment and 10 to 47 years (19y) at follow-up. On non-EF tests, performance agreed with those of IQ-matched controls (four males, two females; mean age 16y 6mo [SD 6mo]; mean FIQ 62.3 [SD 13.4]). On EF tests those who initiated treatment after 2 years 6 months of age performed poorly. In patients with BH4 deficiency, replacement therapy should be started in the first weeks or months of life. Patients diagnosed before the age of 2 years 6 months obtain normal EF, which suggests dopamine may play a critical role in ensuring stable development of EF in early life.

Regulation of GTP cyclohydrolase I expression by orphan receptor Nurr1 in cell culture and in vivo

Nurr1 is an orphan nuclear transcription factor essential for the terminal differentiation of dopamine (DA) neurons in the ventral midbrain (VM). To identify the Nurr1-target genes, we carried out microarray and quantitative real-time PCR analyses of Nurr1 null and wild-type mice in VM at embryonic day (E) 12.5 and shortly after birth (P0). In addition to the absence of mRNAs of DA synthesizing enzymes, the guanosine 5'-triphosphate (GTP) cyclohydrolase I (GTPCH) was also substantially reduced in the VM of Nurr1-null mice. GTPCH is the first enzyme in the synthesis pathway of tetrahydrobiopterin (BH4), an essential cofactor for tyrosine hydroxylase in DA synthesis. In the mouse, Nurr1 and GTPCH mRNA were first detected at E10.5, and GTPCH transcription paralleled that of Nurr1. Small interfering RNA targeted against Nurr1 decreases GTPCH expression in MC3T3-E1 osteoblasts in cell culture. Cotransfection of Nurr1 and the GTPCH-luciferase (luc) reporter increased the luc activity by about threefold in N2A cells. Additional analysis using 5'-deletions and mutants revealed that Nurr1 activates GTPCH transcription indirectly through the proximal promoter region, in the absence of the nerve growth factor-induced clone B (NGFI-B) responsive element-like sites, similarly, as recently reported for DA transporter regulation by Nurr1.

Analysis of plasma biopterin levels in psychiatric disorders suggests a common BH4 deficit in schizophrenia and schizoaffective disorder

Tetrahydrobiopterin (BH4) is an essential cofactor for amine neurotransmitter synthesis. BH4 also stimulates and modulates the glutamatergic system, and regulates the synthesis of nitric oxide by nitric oxide synthases. A connection between BH4 deficiencies and psychiatric disorders has been previously reported; major depression and obsessive-compulsive disorder have been found in subjects with a BH4 deficiency disorder and more recently we have observed a robust plasma deficit of biopterin (a measure of BH4), in a large group of schizophrenic patients compared to control subjects. To extend our previous finding in schizophrenia, we analyzed plasma biopterin levels from patients with schizoaffective and bipolar disorders. A significant difference in biopterin was seen among the diagnostic groups (P < 0.0001). Post hoc analyses indicated significant biopterin deficits relative to the normal control group for the schizoaffective group, who had biopterin levels comparable to the schizophrenic group. Bipolar disorder subjects had plasma biopterin levels that were higher that the schizoaffective disorder group and significantly higher than the schizophrenic group. The demonstrated significant biopterin deficit in both schizophrenia and schizoaffective disorder, may suggest an etiological role of a BH4 deficit in these two disorders, via dysregulation of neurotransmitter systems.

RAMEDIS: the rare metabolic diseases database

The RAMEDIS system is a platform-independent, web-based information system for rare diseases based on individual case reports. It was developed in close cooperation with clinical partners and collects information on rare metabolic diseases in extensive detail (e.g. symptoms, laboratory findings, therapy and genetic data). This combination of clinical and genetic data enables the analysis of genotype-phenotype correlations. By using largely standardised medical terms and conditions, the contents of the database are easy to compare and analyse. In addition, a convenient graphical user interface is provided by every common web browser. RAMEDIS supports an extendable number of different genetic diseases and enables cooperative studies. Furthermore, use of RAMEDIS should lead to advances in epidemiology, integration of molecular and clinical data, and generation of rules for therapeutic intervention and identification of new diseases.

AVAILABILITY

RAMEDIS is available from http://www.ramedis.de

CONTACT

Thoralf Töpel (thoralf.toepel@uni-bielefeld.de).

A murine model for human sepiapterin-reductase deficiency

Tetrahydrobiopterin (BH(4)) is an essential cofactor for several enzymes, including all three forms of nitric oxide synthases, the three aromatic hydroxylases, and glyceryl-ether mono-oxygenase. A proper level of BH(4) is, therefore, necessary for the metabolism of phenylalanine and the production of nitric oxide, catecholamines, and serotonin. BH(4) deficiency has been shown to be closely associated with diverse neurological psychiatric disorders. Sepiapterin reductase (SPR) is an enzyme that catalyzes the final step of BH(4) biosynthesis. Whereas the number of cases of neuropsychological disorders resulting from deficiencies of other catalytic enzymes involved in BH(4) biosynthesis and metabolism has been increasing, only a handful of cases of SPR deficiency have been reported, and the role of SPR in BH(4) biosynthesis in vivo has been poorly understood. Here, we report that mice deficient in the Spr gene (Spr(-/-)) display disturbed pterin profiles and greatly diminished levels of dopamine, norepinephrine, and serotonin, indicating that SPR is essential for homeostasis of BH(4) and for the normal functions of BH(4)-dependent enzymes. The Spr(-/-) mice exhibit phenylketonuria, dwarfism, and impaired body movement. Oral supplementation of BH(4) and neurotransmitter precursors completely rescued dwarfism and phenylalanine metabolism. The biochemical and behavioral characteristics of Spr(-/-) mice share striking similarities with the symptoms observed in SPR-deficient patients. This Spr mutant strain of mice will be an invaluable resource to elucidate many important issues regarding SPR and BH(4) deficiencies.

Long-term outcome and neuroradiological findings of 31 patients with 6-pyruvoyltetrahydropterin synthase deficiency

Tetrahydrobiopterin (BH(4)) deficiency is an autosomal recessive disorder caused by enzyme defects in the biosynthesis or recycling of BH(4). Patients with BH(4) deficiency present with severe neurological signs and symptoms and require a different treatment from classical phenylketonuria. During the last 12 years, 31 cases of BH(4) deficiency were identified in our department. They were all classified as 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. They were diagnosed at the ages of 2.5-48 months and treated with BH(4), L-dopa and 5-hydroxytryptophan immediately after diagnosis. The average development quotients (DQ) at diagnosis and after treatment for more than 3 years were 53+/- 16, and 78+/- 15, respectively. A significant negative correlation was observed between the level of the DQ and the age at which treatment was commenced (r = -0.751, p = 0.002). Developmental profiles were uneven. Language, adaptability and at later age mathematics were particularly weak areas. Only two patients achieved a good performance in mathematics. Eleven patients who were treated with drugs from ages of 2.9-48 months had neuroradiological scanning. Computed tomography disclosed calcification in lentiform nuclei in one patient and magnetic resonance imaging disclosed delayed myelination and abnormal high intensity signal in cerebral white matter in all of them. Even though most of abnormalities were reversible, small patchy or spotted areas were still present on these regions after treatment for 10-46 months. In summary, our study supports the substantial efficacy of the current therapeutic approach in PTPS deficiency of normalizing amine neurotransmitters with three drugs as early as possible. For the first time, calcifications could be detected in patients with PTPS deficiency. Abnormalities in white matter on magnetic resonance imaging were not related to clinical manifestations and most were reversible.

Genetically rescued tetrahydrobiopterin-depleted mice survive with hyperphenylalaninemia and region-specific monoaminergic abnormalities

One of the possibly mutated genes in DOPA-responsive dystonia (DRD, Segawa's disease) is the gene encoding GTP cyclohydrolase I, which is the rate-limiting enzyme for tetrahydrobiopterin (BH4) biosynthesis. Based on our findings on 6-pyruvoyltetrahydropterin synthase (PTS) gene-disrupted (Pts(-/-)) mice, we suggested that the amount of tyrosine hydroxylase (TH) protein in dopaminergic nerve terminals is regulated by the intracellular concentration of BH4. In this present work, we rescued Pts(-/-) mice by transgenic introduction of human PTS cDNA under the control of the dopamine beta-hydroxylase promoter to examine regional differences in the sensitivity of dopaminergic neurons to BH4-insufficiency. The DPS-rescued (Pts(-/-), DPS) mice showed severe hyperphenylalaninemia. Human PTS was efficiently expressed in noradrenergic regions but only in a small number of dopaminergic neurons. Biopterin and dopamine contents, and TH activity in the striatum were poorly restored compared with those in the midbrain. TH-immunoreactivity in the lateral region of the striatum was far weaker than that in the medial region or in the nucleus accumbens. We concluded that dopaminergic nerve terminals projecting to the lateral region of the striatum are the most sensitive to BH4-insufficiency. Biochemical and pathological changes in DPS-rescued mice were similar to those in human malignant hyperphenylalaninemia and DRD.

Sepiapterin reductase deficiency: a congenital dopa-responsive motor and cognitive disorder

This study presents the clinical findings on seven children from Malta (population 385,000). All of them had early motor delay and a significant degree of cognitive impairment. Diurnal variation of the motor impairments was clear in six out of seven of the subjects and oculogyric crises occurred from an early stage also in six out of the seven. Five out of seven had clear evidence of dystonia but the early picture was dominated by hypotonia in five. Two had early Parkinsonian tremor and chorea was seen in four, although in two this was attributable to the use of L-dopa. Three had early bulbar involvement. In all, although minor motor problems persisted, the response to L-dopa was dramatic and there was a need to balance improvement in dystonia against aggravation of chorea. The majority were not able to walk until they were treated. Increased doses of L-dopa were required in hot weather, to which they were sensitive. Despite a good response of improved motor ability and abolition of oculogyric crises, there was no obvious change in cognitive function with learning remaining in the moderate impairment range. This report widens the phenotype of dopa-responsive motor disorders and the range of young children with primary motor delay (cerebral palsy) who need a clinical trial of L-dopa. All of the subjects had the same novel mutation in the tetrahydrobiopterin pathway involving sepiapterin reductase, and no abnormality in the gene encoding guanosine triphosphate cyclohydrolase 1. Clinically and molecularly the condition shows autosomal recessive inheritance.

Phenylalanine loading as a diagnostic test for DRD: interpreting the utility of the test

Phenylalanine loading has been proposed as a diagnostic test for autosomal dominant DRD (dopa-responsive dystonia), and recently, a phenylalanine/tyrosine (phe/tyr) ratio of 7.5 after 4 h was reported as diagnostic of DRD. To test the utility of this test in another sample with DRD, we administered an oral challenge of phenylalanine (100 mg/kg) to 11 individuals with DRD and one non-manifesting gene carrier. Only 6/12 had a 4 h phe/tyr ratio of greater than 7.5, suggesting that additional parameters must be set to avoid missing the diagnosis of DRD, including the need for the plasma phenylalanine to reach a minimum level 600 in order for the test to be valid. We propose that in cases where this minimum plasma phenylalanine level is not reached, plasma tetrahydrobiopterin should be measured or alternatively other symptomatic family members should be screened.

Dihydropteridine reductase deficiency in man: from biology to treatment

In 1975, dihydropteridine reductase (DHPR) deficiency was first recognized as a cause of tetrahydrobiopterin (BH(4)) deficiency, leading to hyperphenylalaninemia (HPA) and impaired biogenic amine deficiency. So far, more than 150 patients scattered worldwide have been reported and major progresses have been made in the understanding of physiopathology, screening, diagnosis, treatment, and molecular genetics of this inherited disease. Present knowledge on different aspects of DHPR deficiency, largely derived from authors' personal experience, is traced in this article.

Subtle brain dysfunction in treated 6-pyruvoyl-tetrahydropterin synthase deficiency: relationship to motor tasks and neurophysiological tests

6-Pyruvoyl-tetrahydropterin synthase (6PTPS) deficiency is a major cause of biopterin deficiency. 6PTPS patients usually have an elevated serum phenylalanine level, a deficiency of neurotransmitters (serotonin and dopamine), and neurological symptoms, if without treatment. We herein investigated the possibility of neurological dysfunction in early-treated patients. In the study, 12 early-treated 6PTPS patients were studied. Their auditory simple reaction time, movement rhythm variation (MRV), somatosensory evoked potentials to median nerve stimulation, and hand muscle responses to transcranial magnetic stimulation, were measured. MRV is a test of repetitive voluntary movements, and was used with and without auditory cues at 0.3 Hz. The 6PTPS patients had an increased motor threshold but normal motor and sensory central conduction times. They performed very well in simple reactions (6PTPS 208.4+/-16.7 ms, control 200.3+/-11.7 ms, p=0.18), but not in continuous tasks. The continuous performance tests showed that MRV had increased in the 6PTPS patients (with cues: 6PTPS 7.35+/-0.94, control 5.47+/-0.80, p<0.0001; without cues: 6PTPS 9.87+/-1.44, control 6.59+/-0.68, p<0.0001). Without cues, MRV had increased in both the 6PTPS and control groups, but more significantly in the 6PTPS patients (6PTPS 2.51+/-0.97, control 1.25+/-0.42; p=0.0001). Our findings indicate that early-treated 6PTPS patients have subtle neurological dysfunctions. They may not maintain movement rhythm as well as normal subjects, even with external cues. Hence, MRV is a good method to assess motor control.

Characterization of quinonoid-dihydropteridine reductase (QDPR) from the lower eukaryote Leishmania major

Biopterin is required for growth of the protozoan parasite Leishmania and is salvaged from the host through the activities of a novel biopterin transporter (BT1) and broad-spectrum pteridine reductase (PTR1). Here we characterize Leishmania major quinonoid-dihydropteridine reductase (LmQDPR), the key enzyme required for regeneration and maintenance of H(4)biopterin pools. LmQDPR shows good homology to metazoan quinonoid-dihydropteridine reductase and conservation of domains implicated in catalysis and regulation. Unlike other organisms, LmQDPR is encoded by a tandemly repeated array of 8-9 copies containing LmQDPR plus two other genes. QDPR mRNA and enzymatic activity were expressed at similar levels throughout the infectious cycle. The pH optima, kinetic properties, and substrate specificity of purified LmQDPR were found to be similar to that of other qDPRs, although it lacked significant activity for non-quinonoid pteridines. These and other data suggest that LmQDPR is unlikely to encode the dihydrobiopterin reductase activity (PTR2) described previously. Similarly LmQDPR is not inhibited by a series of antifolates showing anti-leishmanial activity beyond that attributable to dihydrofolate reductase or PTR1 inhibition. qDPR activity was found in crude lysates of Trypanosoma brucei and Trypanosoma cruzi, further emphasizing the importance of H(4)biopterin throughout this family of human parasites.

Treatment and outcome of Taiwanese patients with 6-pyruvoyltetrahydropterin synthase gene mutations

Ten cases of tetrahydrobiopterin (BH4) deficiency were identified in 1,337,490 newborns screened in a Chinese population in Taiwan. The high incidence of BH4 deficiency in the Taiwanese population may be explained by a founder effect, since all of the patients revealed 6-pyruvoyltetrahydropterin synthase gene mutations, and grouping N52S and P87S mutations together constituted 88.9% of the disease alleles. BH4 supplementation with restriction of high-protein foods gave control of plasma phenylalanine within normal range, and levodopa itself prevented seizure. However, the average intelligence quotient (IQ) score of these patients was only 76 +/- 14 (56-98). Statistically, the age of starting medication, including 5-hydroxytryptophan (5-HTP), was inversely correlated to IQ scores of these patients. We suggest the combination of BH4, levodopa and 5-HTP as the standard protocol to commence the treatment of BH4 deficiency as early as possible, although prenatal brain damage could have existed.

Catecholamines and serotonin are differently regulated by tetrahydrobiopterin. A study from 6-pyruvoyltetrahydropterin synthase knockout mice

(6R)-L-erythro-5,6,7,8-Tetrahydrobiopterin (BH4) is an essential cofactor for tyrosine hydroxylase (TH), tryptophan hydroxylase, phenylalanine hydroxylase, and nitric-oxide synthase. These enzymes synthesize neurotransmitters, e.g. catecholamines, serotonin, and nitric oxide (NO). We established mice unable to synthesize BH4 by disruption of the 6-pyruvoyltetrahydropterin synthase gene, the encoded protein of which catalyzes the second step of BH4 biosynthesis. Homozygous mice were born at the almost expected Mendelian ratio, but died within 48 h after birth. In the brain of homozygous mutant neonates, levels of biopterin, catecholamines, and serotonin were extremely low. The number of TH molecules was highly dependent on the intracellular concentration of BH4 at nerve terminals. Alteration of the TH protein level by modulation of the BH4 content is a novel regulatory mechanism. Our data showing that catecholaminergic, serotonergic, and NO systems were differently affected by BH4 starvation suggest the possible involvement of BH4 synthesis in the etiology of monoamine-based neurological and neuropsychiatric disorders.

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).