Sepiapterin Reductase Research Articles

Abstract 1210: Biopterin metabolism drives tumor progression

Abstract Previous studies demonstrate that nitric oxide synthases (NOS’s) can become uncoupled during inflammatory disease states. A hallmark of this uncoupling is superoxide production from NOS in lieu of nitric oxide (NO) resulting from a reduced tetrahydrobiopterin:dihydrobiopterin ratio (BH4:BH2 ratio). As BH4 is a necessary cofactor for NO production from NOS, when this ratio is reduced, NOS becomes a peroxynitrite synthase enhancing the pro-inflammatory/pro-survival tumor environment. Our lab demonstrated that NOS is uncoupled in a variety of tumor cells both in vitro and in vivo, as well as in paired human colorectal samples due to a reduced BH4:BH2 ratio and that recoupling NOS in via exogenous BH4 both in vitro and in vivo leads to decreased tumor cell proliferation. To examine the mechanism behind the reduced BH4:BH2 ratio we used the DSS/AOM model of colitis and colon tumorigenesis. Here we demonstrate that BH4:BH2 ratio is reduced in mouse colon tumors vs mouse normal colon tissue, 1.36±0.35 vs 7.1±0.6. We determined that this reduced ratio is due at least in part to direct oxidation of BH4 to BH2, as treatment of colon cells with an NADPH Oxidase inhibitor increased the BH4:BH2 two-fold; however, this is unable to account for the degree of uncoupling associated with tumor cells. Given that inflammation appears to drive NOS uncoupling, we extracted colons from DSS/AOM treated animals and preferentially harvested colonic epithelial cells and colonic tumor cells at different stages of inflammation to assess the molecular and biochemical changes in molecules important in the regulation and production of BH4. The molecules we focused on were: GTP cyclohydrolase-1 (GCH1, rate limiting enzyme in de novo BH4 synthesis), GTP cyclohydrolase 1 feedback regulatory protein (GCHFRP, regulates GCH1 expression), quinoiddihydropteridine reductase (QDPR, necessary for salvage pathway) and sepiapterin reductase (SR, necessary for both de novo synthesis and salvage of BH4). Transcript levels of these molecules in DSS treated epithelial cells showed that GCH1 and SR were upregulated but QDPR was significantly downregulated when compared with untreated cells, potentially leading to an increase in total BH4 but once oxidized to BH2, a decrease in the salvage back to BH4. Our current research investigates the protein levels as well biochemical activity of these molecules in DSS treated epithelial cells, as well as tumor cells compared with normal cells to further understand the molecular component of the decrease in BH4:BH2 ratio in tumors. Note: This abstract was not presented at the meeting. Citation Format: Christopher Rabender, Asim Alam, Mike Waters, Ross Mikkelsen. Biopterin metabolism drives tumor progression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1210. doi:10.1158/1538-7445.AM2015-1210

Valproic acid exposure leads to upregulation and increased promoter histone acetylation of sepiapterin reductase in a serotonergic cell line

Valproic acid (VPA) is a widely used antiepileptic drug and first-line treatment in bipolar disorder, although the mechanisms underlying its therapeutic effects are largely unknown. Recently, the recognition of VPA as an epigenetic drug offers new opportunities for understanding its therapeutic actions. In a rat serotonergic cell line (RN46A) we observed that VPA exposure has a strong upregulatory effect on the gene for sepiapterin reductase (SPR), a key enzyme involved in the tetrahydrobiopterin (BH4) synthetic pathway. BH4 is an essential cofactor in the biosynthesis of neurotransmitters like serotonin, dopamine and noradrenalin, and the BH4 pathway may thus be important in mood biology. Using real-time quantitative PCR we show that VPA, at therapeutically relevant doses, increases the expression of the Spr gene by about 8-fold in RN46A cells. In addition, Spr protein levels in VPA-exposed cells were elevated, as were the intracellular BH4 levels. HDAC inhibitors (HDACI) trichostatin A and sodium butyrate also upregulated Spr, but this was not observed using the VPA-analogue valpromide, which lacks HDAC inhibitory activity. Further examination of this effect revealed that exposure to VPA increased the acetylated histone mark H3K9/K14ac at the Spr promoter. The DNMT inhibitor 5′aza-dC also upregulated Spr by over 8-fold. However, DNA methylation status across the Spr promoter did not change in response to VPA. The BH4 pathway is fundamental to the regulation of neurotransmitters relevant to mood disorders, and this epigenetic effect of VPA at the Spr promoter may represent a novel mechanism through which VPA achieves its therapeutic action.

Urine sepiapterin excretion as a new diagnostic marker for sepiapterin reductase deficiency

Sepiapterin reductase deficiency (SRD) causes depletion of biogenic amines in the brain, early onset motor disorder, and intellectual disability. The diagnostic marker for this rare disease is increased sepiapterin and biopterin in CSF. Through a new analytic methodology we demonstrated accumulation of sepiapterin in urine of four SRD patients several times greater than that found in healthy controls and carriers, regardless of age or treatment. Our findings suggest a new interpretation of current theories of peripheral pterin metabolism and provide a new noninvasive diagnostic tool for children with early onset cryptogenetic developmental delay and/or movement disorder.

Dopa-responsive dystonia--clinical and genetic heterogeneity.

Dopa-responsive dystonia (DRD) encompasses a group of clinically and genetically heterogeneous disorders that typically manifest as limb-onset, diurnally fluctuating dystonia and exhibit a robust and sustained response to levodopa treatment. Autosomal dominant GTP cyclohydrolase 1 deficiency, also known as Segawa disease, is the most common and best-characterized condition that manifests as DRD, but a similar presentation can be seen with genetic abnormalities that lead to deficiencies in tyrosine hydroxylase, sepiapterin reductase or other enzymes that are involved in the biosynthesis of dopamine. In rare cases, DRD can result from conditions that do not affect the biosynthesis of dopamine; single case reports have shown that DRD can be a manifestation of hereditary spastic paraplegia type 11, spinocerebellar ataxia type 3 and ataxia telangiectasia. This heterogeneity of conditions that underlie DRD frequently leads to misdiagnosis, which delays the appropriate treatment with levodopa. Correct diagnosis at an early stage requires use of the appropriate diagnostic tests, which include a levodopa trial, genetic testing (including whole-exome sequencing), cerebrospinal fluid neurotransmitter analysis, the phenylalanine loading test, and enzyme activity measurements. The selection of tests for use depends on the clinical presentation and level of complexity. This Review presents the common and rarer causes of DRD and their clinical features, and considers the most appropriate approaches to ensure early diagnosis and treatment.

Effect of sulfasalazine on human neuroblastoma: analysis of sepiapterin reductase (SPR) as a new therapeutic target.

BackgroundNeuroblastoma (NB) is an aggressive childhood malignancy in children up to 5 years of age. High-stage tumors frequently relapse even after aggressive multimodal treatment, and then show therapy resistance, typically resulting in patient death. New molecular-targeted compounds that effectively suppress tumor growth and prevent relapse with more efficacy are urgently needed. We and others previously showed that polyamines (PA) like spermidine and spermine are essential for NB tumorigenesis and that DFMO, an inhibitor of the key PA synthesis gene product ODC, is effective both in vitro and in vivo, securing its evaluation in NB clinical trials. To find additional compounds interfering with PA biosynthesis, we tested sulfasalazine (SSZ), an FDA-approved salicylate-based anti-inflammatory and immune-modulatory drug, recently identified to inhibit sepiapterin reductase (SPR). We earlier presented evidence for a physical interaction between ODC and SPR and we showed that RNAi-mediated knockdown of SPR expression significantly reduced native ODC enzyme activity and impeded NB cell proliferation.MethodsHuman NB mRNA expression datasets in the public domain were analyzed using the R2 platform. Cell viability, isobologram, and combination index analyses as a result of SSZ treatment with our without DFMO were carried out in NB cell cultures. Molecular protein-ligand docking was achieved using the GRAMM algorithm. Statistical analyses were performed with the Kruskal-Wallis test, 2log Pearson test, and Student’s t test.ResultsIn this study, we show the clinical relevance of SPR in human NB tumors. We found that high SPR expression is significantly correlated to unfavorable NB characteristics like high age at diagnosis, MYCN amplification, and high INSS stage. SSZ inhibits the growth of NB cells in vitro, presumably due to the inhibition of SPR as predicted by computational docking of SSZ into SPR. Importantly, the combination of SSZ with DFMO produces synergistic antiproliferative effects in vitro.ConclusionsThe results suggest the use of SSZ in combination with DFMO for further experiments, and possible prioritization as a novel therapy for the treatment of NB patients.

Influence of the silencing sex-peptide receptor on Bactrocera dorsalis adults and offspring by feeding with ds-spr

RNA interference (RNAi) has been shown to control insect pests using plant dsRNA expression. A key question in potentially applying RNAi is the possible effects on insects after being fed with dsRNA produced by a transgenic plant. Sex peptide receptor (spr) is the key gene that regulates the suppression of female receptivity and induction of oviposition. In this study, the expression level of the spr gene was significantly down-regulated to 52% by feeding Bactrocera dorsalis adults with ds-spr. The RNAi effects of continuous feeding ds-spr to adults led to a highly mortality rate, decreased their egg production capacity and profoundly impacted the eclosion rate of their offspring. Our results demonstrate that RNAi through uninterrupted dsRNA feeding can be used as a strategy to control insect pests. Moreover, the research presented here provides a potential RNAi target gene for controlling B. dorsalis and a theoretical basis for universally applying RNAi in insect pest management.

Reduction of Neuropathic and Inflammatory Pain through Inhibition of the Tetrahydrobiopterin Pathway

Human genetic studies have revealed an association between GTP cyclohydrolase 1 polymorphisms, which decrease tetrahydrobiopterin (BH4) levels, and reduced pain in patients. We now show that excessive BH4 is produced in mice by both axotomized sensory neurons and macrophages infiltrating damaged nerves and inflamed tissue. Constitutive BH4 overproduction in sensory neurons increases pain sensitivity, whereas blocking BH4 production only in these cells reduces nerve injury-induced hypersensitivity without affecting nociceptive pain. To minimize risk of side effects, we targeted sepiapterin reductase (SPR), whose blockade allows minimal BH4 production through the BH4 salvage pathways. Using a structure-based design, we developed a potent SPR inhibitor and show that it reduces pain hypersensitivity effectively with a concomitant decrease in BH4 levels in target tissues, acting both on sensory neurons and macrophages, with no development of tolerance or adverse effects. Finally, we demonstrate that sepiapterin accumulation is a sensitive biomarker for SPR inhibition in vivo.

Functional analysis of sepiapterin reductase in Drosophila melanogaster

Abstract 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.

A comparative structural analysis of sepiapterin reductase from Drosophila by homology modeling

Abstract Sepiapterin reductase (SR) catalyzes the final steps of BH4 biosynthesis. Previously, a gene encoding SR has been cloned and characterized from a Drosophila cDNA library in vitro. The present study reports the identification of another SR gene in the Drosophila genome and the structural characteristics and differences of the two Drosophila SRs, using homology modeling analysis. Homology modeling of SRs for protein structure and function prediction showed that the two SRs have different surface electrostatic distributions and different shapes of the substrate (sepiapterin)-binding sites. These results provide valuable insight into the possibility of diverse functions of Drosophila SRs in vivo.

Inhibition of Sepiapterin Mediated Formation of Dihydrobiopterin and Chemical Redox Cycling by Sulfa Drugs

Sepiapterin reductase (SPR) catalyzes the reduction of sepiapterin to dihydrobiopterin (BH2), a precursor for tetrahydrobiopterin (BH4), a cofactor critical for nitric oxide biosynthesis and alkylglycerol and aromatic amino acid metabolism. SPR also mediates chemical redox cycling, catalyzing one electron reduction of redox active chemicals including quinones; rapid reaction of these radicals with molecular oxygen generates reactive oxygen species (ROS). Using recombinant human SPR, sulfonamide and sulfonylurea based sulfa drugs were found to be potent non‐competitive inibitors of both sepiapterin reduction and redox cycling. The most active inhibitors of sepiapterin reduction (IC50's = 31‐180 nM) were sulfasalazine, sulfathiazole, sulfapyridine, sulfamethoxazole and chlorpropamide. Higher concentrations of the sulfa drugs (IC50's = 0.37‐19.4 µM) were required to inhibit redox cycling. In PC12 cells, which generate catecholamine and monoamine neurotransmitters via BH4‐dependent amino acid hydroxylases, sulfa drugs inhibited both BH2/BH4 biosynthesis and redox cycling. This resulted in decreased production of dopamine and dopamine metabolites, 3, 4‐dihydroxyphenylacetic acid and homovanillic acid, and 5‐hydroxytryptamine. This was reversed by BH4. These data suggest that SPR and BH4‐dependent enzymes, are ‘off‐targets' for sulfa drugs, which may underlie their side effects. AR055073, ES005022.

Combined Sepiapterin Reductase and Methylmalonyl-CoA Epimerase Deficiency in a Second Patient: Cerebrospinal Fluid Polyunsaturated Fatty Acid Level and Follow-Up Under L-DOPA, 5-HTP and BH4 Trials.

Objective/context: We describe the second patient presenting the combination of two homoallelic homozygous nonsense mutations in two genes distant from 1.8Mb in the chromosome 2p13-3, the methylmalonyl-CoA epimerase gene (MCEE) and the sepiapterin reductase gene (SPR). The patient was born from consanguineous parents. He has presented a moderate but constant methylmalonic acid (MMA) excretion in urine associated with a mental retardation. The first homozygous mutation was identified in the MCEE gene (c.139C>T; p.Arg47*). Progressive dystonia and cataplexy narcolepsy led to diagnose the second homozygous mutation in the SPR gene: c.751A>T; p.Lys251*. Sepiapterin reductase deficiency (SRD) was characterized by a defect in tetrahydrobiopterin (BH4), the cofactor of several hydroxylases needed for the synthesis of neurotransmitters. A treatment with L-DOPA/carbidopa and 5-HTP dramatically improved the dystonic posture, the mood and the hypersomnia, proving that the pathogenesis was due to SRD. A supplementation with BH4 did not induce additional clinical benefit, although HVA and HIAA increased in CSF. The polyunsaturated fatty acids were measured in CSF as the markers of the neuronal stress. We have shown that DHA and its precursor EPA were high before and during the time course of the different treatments. The patient has inherited two copies of the two mutations from his consanguineous parents in the MCEE and SPR genes in the chromosome 2p13-3. DHA and EPA increased in CSF as a response to the neuronal stress induced by the defect in neurotransmitters or the altered metabolism of the odd-chain fatty acids and cholesterol.

Dopamine-Responsive Growth-Hormone Deficiency and Central Hypothyroidism in Sepiapterin Reductase Deficiency.

Sepiapterin reductase (SR) deficiency is a rare autosomal recessively inherited error of tetrahydrobiopterin (BH4) biosynthesis, resulting in disturbed dopaminergic and serotonergic neurotransmission. The clinical phenotype is characterized by dopa-responsive movement disorders including muscular hypotonia, dystonia, and parkinsonism. Due to the rarity of the disease, the phenotype of SR deficiency is far from being completely understood. Here, we report a 7-year-old boy, who was referred for diagnostic evaluation of combined psychomotor retardation, spastic tetraplegia, extrapyramidal symptoms, and short stature. Due to discrepancy between motor status and mental condition, analyses of biogenic amines and pterins in CSF were performed, leading to the diagnosis of SR deficiency. The diagnosis was confirmed by a novel homozygous mutation c.530G>C; p.(Arg177Pro) in exon 2 of the SPR gene. Because of persistent short stature, systematic endocrinological investigations were initiated. Insufficient growth-hormone release in a severe hypoglycemic episode after overnight fasting confirmed growth-hormone deficiency as a cause of short stature. In addition, central hypothyroidism was present. A general hypothalamic affection could be excluded. Since dopamine is known to regulate growth-hormone excretion, IGF-1, IGF-BP3, and peripheral thyroid hormone levels were monitored under L-dopa/carbidopa supplementation. Both growth-hormone-dependent factors and thyroid function normalized under treatment. This is the first report describing growth-hormone deficiency and central hypothyroidism in SR deficiency. It extends the phenotypic spectrum of the disease and identifies dopamine depletion as cause for the endocrinological disturbances.

Sulfa drugs inhibit sepiapterin reduction and chemical redox cycling by sepiapterin reductase.

Sepiapterin reductase (SPR) catalyzes the reduction of sepiapterin to dihydrobiopterin (BH2), the precursor for tetrahydrobiopterin (BH4), a cofactor critical for nitric oxide biosynthesis and alkylglycerol and aromatic amino acid metabolism. SPR also mediates chemical redox cycling, catalyzing one-electron reduction of redox-active chemicals, including quinones and bipyridinium herbicides (e.g., menadione, 9,10-phenanthrenequinone, and diquat); rapid reaction of the reduced radicals with molecular oxygen generates reactive oxygen species (ROS). Using recombinant human SPR, sulfonamide- and sulfonylurea-based sulfa drugs were found to be potent noncompetitive inhibitors of both sepiapterin reduction and redox cycling. The most potent inhibitors of sepiapterin reduction (IC50s = 31-180 nM) were sulfasalazine, sulfathiazole, sulfapyridine, sulfamethoxazole, and chlorpropamide. Higher concentrations of the sulfa drugs (IC50s = 0.37-19.4 μM) were required to inhibit redox cycling, presumably because of distinct mechanisms of sepiapterin reduction and redox cycling. In PC12 cells, which generate catecholamine and monoamine neurotransmitters via BH4-dependent amino acid hydroxylases, sulfa drugs inhibited both BH2/BH4 biosynthesis and redox cycling mediated by SPR. Inhibition of BH2/BH4 resulted in decreased production of dopamine and dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, and 5-hydroxytryptamine. Sulfathiazole (200 μM) markedly suppressed neurotransmitter production, an effect reversed by BH4. These data suggest that SPR and BH4-dependent enzymes, are "off-targets" of sulfa drugs, which may underlie their untoward effects. The ability of the sulfa drugs to inhibit redox cycling may ameliorate ROS-mediated toxicity generated by redox active drugs and chemicals, contributing to their anti-inflammatory activity.

Deficiencias de tetrahidrobiopterina (BH4): diagnóstico y tratamiento

Tetrahydrobiopterin (BH4) is an enzyme cofactor of phenylalanine hydroxylase, tyrosine hydroxylase and tryptophan hydroxylase. Three different enzymes affect BH4 synthesis: guanosine triphosphate cyclohydrolase I (GTP CH 1), 6-piruvoil tetrahydropterin synthase (PTPS), sepiapterin reductase (SR) and dihydropteridine reductase (DHPR) affects regeneration. BH4 deficiency causes defects in monoaminergic neurotransmitters synthesis and can be or not associated with hyperphenylalaninemia (HPA). Symptoms often begin in the first months of life with mental retardation, dystonic movements and posture, temperature control disorders, seizures, abnormal posture and tone, salivation and swallowing difficulties. Diagnosis is based on the following tests: pterins in urine, neurotransmitters and pterins in cerebrospinal fluid, reduced enzyme activity (in blood or fibroblasts) and mutational analysis. Treatment should be directed to normalize blood Phe levels and brain neurotransmitters with the administration of BH4 10 mg / kg / d, L-DOPA 10 mg/kg/day and 5-OH-tryptophan, 5 to 6 mg/kg/day. LDOPA should be given with carbidopa in order to inhibit the destruction of the L-dopa by the carboxylase. We describe 3 patients with BH4 deficiency treated at the Ramon y Cajal Hospital. All of them had a good neurological outcome with almost normal mental development.

Identification of Bacterial Factors Involved in Type 1 Fimbria Expression using an Escherichia coli K12 Proteome Chip

Type 1 fimbriae are filamentous structures on Escherichia coli. These structures are important adherence factors. Because binding to the host cells is the first step of infection, type 1 fimbria is an important virulence factor of pathogenic E. coli. Expression of type 1 fimbria is regulated by a phase variation in which each individual bacterium can alternate between fimbriated (phase-ON) and nonfimbriated (phase-OFF) states. The phase variation is regulated by the flipping of the 314-bp fimS fragment, which contains the promoter driving the expression of the genes required for the synthesis of type 1 fimbria. Thus, the bacterial proteins able to interact with fimS are likely to be involved in regulating the expression of type 1 fimbria. To identify novel type 1 fimbria-regulating factors, we used an E. coli K12 proteome chip to screen for the bacterial factors able to interact with a 602-bp DNA fragment containing fimS and its adjacent regions. The Spr protein was identified by the proteome chip-based screening and further confirmed to be able to interact with fimS by electrophoretic mobility shift assay. Deletion of spr in the neonatal meningitis E. coli strain RS218 significantly increased the ratio of the bacterial colonies that contained the type 1 fimbria phase-ON cells on agar plates. In addition, Spr interfered with the interactions of fimS with the site-specific recombinases, FimB and FimE, which are responsible for mediating the flipping of fimS. These results suggest that Spr is involved in the regulation of type 1 fimbria expression through direct interaction with the invertible element fimS. These findings facilitate our understanding of the regulation of type 1 fimbria.

‘That DAT’ gene that causes dystonia-parkinsonism: broadening the phenotype

Dopamine transporter (DAT) deficiency, a recessive disorder due to mutations in the encoding SLC63 gene, was first described by Kurian et al. (2009, 2011). The typical phenotype originally reported was infantile dystonia-parkinsonism with a characteristic metabolic profile in the CSF, namely a raised homovanillic acid: 5-hydroxyindoleacetic acid (HVA:5-HIAA) ratio, usually in excess of 4.0. Presynaptic DAT, expressed by dopaminergic neurons, is responsible for reuptake of extracellular dopamine in a Na+/Cl−dependent manner (Torres et al., 2003). In this issue of Brain, Ng et al. (2014) describe a new cohort of patients with dopamine transporter deficiency syndrome (DTDS) and evaluate the functional consequences of SLC6A3 mutations using in vitro heterologous expression. The clinical significance of this paper is the new phenotypic associations. In addition to the classical presenation—infantile-onset progressive parkinsonism-dystonia—Ng et al. (2014) report cases who presented atypically, later in childhood and with a milder disease course. The new cohort consisted of eight cases with a median age at diagnosis of 13 years; one patient was diagnosed at 34 years. All eight patients had either homozygous or compound heterozygous missense or splice site mutations in the SLC63 gene. Three of eight cases, from one kindred, had juvenile onset progressive parkinsonism-dystonia. Notably, all three brothers had a normal birth history and neonatal course, and achieved normal early developmental milestones in infancy. At 10–11 years of age, they all developed a tremor affecting the head, with progression of symptoms in their 20 s. Another case, despite having infantile onset, survived into his fourth decade. Ng et al. (2014) also present evidence for dysfunction of the DAT gene in the new cases. In vitro studies of mutant transporter showed several defects in dopamine transporter function, including absent or reduced dopamine uptake, reduced DAT cell surface expression, and reduced affinity for dopamine. Loss of post-translational dopamine transporter glycosylation and failure of amphetamine-mediated dopamine efflux were also detected. The degree of dysfunction was greater for mutations causing infantile-onset than for those causing juvenile-onset disease. For example, the A314V mutation associated with atypical DTDS exhibited the highest residual dopamine uptake capacity compared with the mutations causing infantile DTDS. This report expands the phenotypic spectrum of DTDS, which includes presentation in infancy (early onset, rapidly-progressive disease), and in childhood/adolescence (later onset, slower disease progression). Genotype–phenotype analysis in this cohort, consistent with several other enzymatic recessive disorders, suggests that the higher residual dopamine transporter activity contributed to postponing disease presentation or slowing down progression in these late-onset cases. What is the significance of this report for clinicians, in particular paediatric neurologists and movement disorders specialists? DTDS is probably under-recognized. To date, apart from the original report (Kurian et al., 2009, 2011), there has been only one other study describing similar early-onset cases (Henriksen et al., 2012), and overall there are only a handful of cases in the literature. This study highlights the need to consider DTDS in the differential diagnosis for both infantile- and juvenile-onset movement disorders presenting with tremor and dystonia-parkinsonism. Some of these cases may be masquerading as cerebral palsy or other conditions that present with juvenile dystonia and parkinsonism (Schneider and Bhatia, 2010). Given that some of the patients with DTDS have oculogyric crises, other disorders in the dopamine synthesis pathway such as tyrosine hydroxylase deficiency and sepiapterin reductase deficiency enter into the differential diagnosis. Moreover, because tremor was common, juvenile parkinsonism needs to be kept in mind, particularly due to parkin gene mutations. However, in this regard, the DAT SPECT scan is normal in DTDS, whereas most cases of degenerative juvenile parkinsonism, including those arising from parkin gene mutations, will have an abnormal DAT scan. Hence the combination of the CSF analysis, showing a raised HVA/HIAA ratio, and a normal DAT scan, should be a clear pointer for DTDS, which of course can be confirmed on genetic testing. Finally, it is interesting to note that the cases described by Ng et al. (2014) are not only from an Asian background, but also include Italian and mixed European ancestry, and it is likely that these conditions are present in all countries. The message for clinicians is, when faced with a patient with infantile or adolescent dystonia-parkinsonsim, even if presenting in adulthood, don’t forget to consider ‘that DAT’ gene.

Clinical and genetic studies in a family with a novel mutation in the sepiapterin reductase gene

Sepiapterin reductase deficiency is a rare, but treatable inherited disorder of tetrahydrobiopterin and neurotransmitter metabolism. This disorder is most probably underdiagnosed. To date, only 44 cases have been described in the literature. We present the clinical and genetic investigations in a family with a complex movement disorder. We examined two affected sisters and three healthy family members. The cerebrospinal fluid was analyzed for neurotransmitter and pterins, and the sepiapterin reductase gene (SPR) was sequenced. The sisters had a complex movement disorders with dystonia and diurnal fluctuations. Both had oculogyric crises, and the older sister also hypersomnia. Both sisters had raised prolactin levels twice above the reference level. One sister had a dramatic response to levodopa, the other responded, but developed dyskinesia despite low doses. Both patients improved dramatically over time with levodopa (2.3 and 1.5 mg/kg/day). Very low levels of homovanillic acid and 5-hydroxyindoleacetic acid and increased levels of sepiapterin and dihydrobiopterin were measured in the cerebrospinal fluid before treatment. DNA analyses revealed a novel homozygous mutation in exon 2 in the SPR gene, c.364A>G/p.(Tyr123Cys), located in a highly conserved region in the gene. Both parents and the healthy sister were carriers for the same mutation. A new homozygous mutation in the SPR gene was found in two sisters with dopa-responsive dystonia. This important and treatable neurotransmitter disorder must be considered in patients with a complex movement disorder with diurnal fluctuations with or without intellectual impairment. Patients with these symptoms should undergo levodopa trial, cerebrospinal fluid investigations, and genetic analyses.

Utility of the Biosynthetic Folate Pathway for Targets in Antimicrobial Discovery.

The need for new antimicrobials is great in face of a growing pool of resistant pathogenic organisms. This review will address the potential for antimicrobial therapy based on polypharmacological activities within the currently utilized bacterial biosynthetic folate pathway. The folate metabolic pathway leads to synthesis of required precursors for cellular function and contains a critical node, dihydrofolate reductase (DHFR), which is shared between prokaryotes and eukaryotes. The DHFR enzyme is currently targeted by methotrexate in anti-cancer therapies, by trimethoprim for antibacterial uses, and by pyrimethamine for anti-protozoal applications. An additional anti-folate target is dihyropteroate synthase (DHPS), which is unique to prokaryotes as they cannot acquire folate through dietary means. It has been demonstrated as a primary target for the longest standing antibiotic class, the sulfonamides, which act synergistically with DHFR inhibitors. Investigations have revealed most DHPS enzymes possess the ability to utilize sulfa drugs metabolically, producing alternate products that presumably inhibit downstream enzymes requiring the produced dihydropteroate. Recent work has established an off-target effect of sulfonamide antibiotics on a eukaryotic enzyme, sepiapterin reductase, causing alterations in neurotransmitter synthesis. Given that inhibitors of both DHFR and DHPS are designed to mimic their cognate substrate, which contain shared substructures, it is reasonable to expect such “off-target” effects. These inhibitors are also likely to interact with the enzymatic neighbors in the folate pathway that bind products of the DHFR or DHPS enzymes and/or substrates of similar substructure. Computational studies designed to assess polypharmacology reiterate these conclusions. This leads to hypotheses exploring the vast utility of multiple members of the folate pathway for modulating cellular metabolism, and includes an appealing capacity for prokaryotic-specific polypharmacology for antimicrobial applications.

LC-MS/MS Analysis of Cerebrospinal Fluid Metabolites in the Pterin Biosynthetic Pathway.

The analysis of (6R)-5,6,7,8-tetrahydrobiopterin (BH4) and neopterin in cerebrospinal fluid (CSF) is often used to identify defects in the pterin biosynthetic pathway affecting monoamine metabolism that can lead to pediatric neurotransmitter diseases. Low levels of BH4 and neopterin alone may not be sufficient to determine the defect, and further testing is often required. We have developed a sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method for determination of BH4, 7,8-dihydrobiopterin (BH2), neopterin, and sepiapterin in CSF, which provides a more comprehensive evaluation of the pterin pathway. The method utilizes labeled stable isotopes as internal standards and allows for a fast 10-minute analysis by LC/MS/MS over a linear working range of 3 to 200nmol/L. Total analytical imprecision is less than 14.4% for all pterin metabolites. Accuracy for BH4 and neopterin was determined by comparing data obtained by an alternative method using HPLC with EC and fluorescence detection. Excellent correlation was demonstrated for BH4 (r = 0.9646, 1/slope = 0.9397; n = 28; concentration range 3 to 63nmol/L) and neopterin (r = 0.9919, 1/slope = 0.9539; n = 13; concentration range 5 to 240nmol/L). CSF specimens from patients diagnosed with inborn errors of sepiapterin reductase (SR), 6-pyruvoyl-tetrahydropterin synthase (PTPS), dihydropteridine reductase (DHPR), and guanosine triphosphate cyclohydrolase (GTPCH) have been analyzed, and distinct pterin metabolite patterns were consistent with the initial diagnosis. This method differentiates patients with DHPR and SR deficiency from other pterin defects (GTPCH and PTPS) and will be useful for the diagnosis of specific defects in the pterin biosynthetic pathway.

Very early pattern of movement disorders in sepiapterin reductase deficiency

Sepiapterin reductase deficiency (SRD; Online Mendelian Inheritance in Man *182125) is a rare disorder of biogenic amines synthesis caused by mutations of the SPR gene on chromosome 2p14-p12.1 The most common presenting symptoms of SRD are developmental delay and axial hypotonia.2 The few patients observed during the very early stage of the disease suggested a peculiar pattern of neurologic impairment.3,4 With the aim of contributing to this topic, we report on a new case diagnosed and treated since the first months of life.