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Opladen T, López-Laso E, Cortès-Saladelafont E, Pearson TS, Sivri HS, Yildiz Y, Assmann B, Kurian MA, Leuzzi V, Heales S, Pope S, Porta F, García-Cazorla A, Honzík T, Pons R, Regal L, Goez H, Artuch R, Hoffmann GF, Horvath G, Thöny B, Scholl-Bürgi S, Burlina A, Verbeek MM, Mastrangelo M, Friedman J, Wassenberg T, Jeltsch K, Kulhánek J, Kuseyri Hübschmann O. Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH 4) deficiencies. Orphanet J Rare Dis 2020; 15:126. [PMID: 32456656 PMCID: PMC7251883 DOI: 10.1186/s13023-020-01379-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 04/07/2020] [Indexed: 12/21/2022] Open
Abstract
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.
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Affiliation(s)
- Thomas Opladen
- Division of Child Neurology and Metabolic Disorders, University Children's Hospital, Heidelberg, Germany.
| | - Eduardo López-Laso
- Pediatric Neurology Unit, Department of Pediatrics, University Hospital Reina Sofía, IMIBIC and CIBERER, Córdoba, Spain
| | - Elisenda Cortès-Saladelafont
- Inborn errors of metabolism Unit, Institut de Recerca Sant Joan de Déu and CIBERER-ISCIII, Barcelona, Spain
- Unit of Pediatric Neurology and Metabolic Disorders, Department of Pediatrics, Hospital Germans Trias i Pujol, and Faculty of Medicine, Universitat Autònoma de Barcelona, Badalona, Spain
| | - Toni S Pearson
- Department of Neurology, Washington University School of Medicine, St. Louis, USA
| | - H Serap Sivri
- Department of Pediatrics, Section of Metabolism, Hacettepe University, Faculty of Medicine, 06100, Ankara, Turkey
| | - Yilmaz Yildiz
- Department of Pediatrics, Section of Metabolism, Hacettepe University, Faculty of Medicine, 06100, Ankara, Turkey
| | - Birgit Assmann
- Division of Child Neurology and Metabolic Disorders, University Children's Hospital, Heidelberg, Germany
| | - Manju A Kurian
- Developmental Neurosciences, UCL Great Ormond Street-Institute of Child Health, London, UK
- Department of Neurology, Great Ormond Street Hospital, London, UK
| | - Vincenzo Leuzzi
- Unit of Child Neurology and Psychiatry, Department of Human Neuroscience, Sapienza University of Rome, Rome, Italy
| | - Simon Heales
- Neurometabolic Unit, National Hospital, Queen Square, London, UK
| | - Simon Pope
- Neurometabolic Unit, National Hospital, Queen Square, London, UK
| | - Francesco Porta
- Department of Pediatrics, AOU Città della Salute e della Scienza, Torino, Italy
| | - Angeles García-Cazorla
- Inborn errors of metabolism Unit, Institut de Recerca Sant Joan de Déu and CIBERER-ISCIII, Barcelona, Spain
| | - Tomáš Honzík
- Department of Paediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic
| | - Roser Pons
- First Department of Pediatrics of the University of Athens, Aghia Sofia Hospital, Athens, Greece
| | - Luc Regal
- Department of Pediatric, Pediatric Neurology and Metabolism Unit, UZ Brussel, Brussels, Belgium
| | - Helly Goez
- Department of Pediatrics, University of Alberta Glenrose Rehabilitation Hospital, Edmonton, Canada
| | - Rafael Artuch
- Clinical biochemistry department, Institut de Recerca Sant Joan de Déu, CIBERER and MetabERN Hospital Sant Joan de Déu, Barcelona, Spain
| | - Georg F Hoffmann
- Division of Child Neurology and Metabolic Disorders, University Children's Hospital, Heidelberg, Germany
| | - Gabriella Horvath
- Department of Pediatrics, Division of Biochemical Genetics, BC Children's Hospital, University of British Columbia, Vancouver, BC, Canada
| | - Beat Thöny
- Division of Metabolism, University Children's Hospital Zurich, Zürich, Switzerland
| | - Sabine Scholl-Bürgi
- Clinic for Pediatrics I, Medical University of Innsbruck, Anichstr 35, Innsbruck, Austria
| | - Alberto Burlina
- U.O.C. Malattie Metaboliche Ereditarie, Dipartimento della Salute della Donna e del Bambino, Azienda Ospedaliera Universitaria di Padova - Campus Biomedico Pietro d'Abano, Padova, Italy
| | - Marcel M Verbeek
- Departments of Neurology and Laboratory Medicine, Alzheimer Centre, Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands
| | - Mario Mastrangelo
- Unit of Child Neurology and Psychiatry, Department of Human Neuroscience, Sapienza University of Rome, Rome, Italy
| | - Jennifer Friedman
- UCSD Departments of Neuroscience and Pediatrics, Rady Children's Hospital Division of Neurology; Rady Children's Institute for Genomic Medicine, San Diego, USA
| | - Tessa Wassenberg
- Department of Pediatric, Pediatric Neurology and Metabolism Unit, UZ Brussel, Brussels, Belgium
| | - Kathrin Jeltsch
- Division of Child Neurology and Metabolic Disorders, University Children's Hospital, Heidelberg, Germany
| | - Jan Kulhánek
- Department of Paediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic.
| | - Oya Kuseyri Hübschmann
- Division of Child Neurology and Metabolic Disorders, University Children's Hospital, Heidelberg, Germany
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Ferreira CR, van Karnebeek CDM, Vockley J, Blau N. A proposed nosology of inborn errors of metabolism. Genet Med 2018; 21:102-106. [PMID: 29884839 PMCID: PMC6286709 DOI: 10.1038/s41436-018-0022-8] [Citation(s) in RCA: 130] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Revised: 01/29/2018] [Accepted: 03/20/2018] [Indexed: 01/13/2023] Open
Abstract
Purpose We propose a nosology for inborn errors of metabolism that builds on their recent redefinition. Methods We established a strict definition of criteria in order to develop a self-consistent schema for inclusion of a disorder into the nosology. Results We identified 1,015 well-characterized inborn errors of metabolism described in the literature. In addition, there are 111 less well-characterized conditions that may be inborn errors but do not meet strict criteria for inclusion in the current nosology. Conclusion We provide a master list of all currently recognized inborn errors of metabolism grouped according to their pathophysiological basis, with the hope of setting a standard against which new errors should be defined, as well as to promote awareness and foster collaboration in the area. With the rapid advances in the field of genetics in recent years, it is likely that this nosology will need to be updated in the near future, a process that will benefit from broader input and collaboration of experts in the field in order to improve future versions of the proposed classification.
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Affiliation(s)
- Carlos R Ferreira
- National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, USA. .,Division of Genetics and Metabolism, Children's National Health System, Washington, DC, USA.
| | - Clara D M van Karnebeek
- Departments of Pediatrics and Clinical Genetics, Academic Medical Centre, Amsterdam, The Netherlands.,Department of Pediatrics, Centre for Molecular Medicine and Therapeutics, University of British Columbia, Vancouver, BC, Canada
| | - Jerry Vockley
- Department of Pediatrics, University of Pittsburgh School of Medicine, Department of Human Genetics, Graduate School of Public Health, Pittsburgh, Pennsylvania, USA
| | - Nenad Blau
- Dietmar-Hopp Metabolic Center, University Children's Hospital, Heidelberg, Germany
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Abstract
Dopa-responsive dystonia (DRD) has a classic presentation of childhood or adolescent-onset dystonia, mild parkinsonism, marked diurnal fluctuations, improvement with sleep or rest, and a dramatic and sustained response to low doses of L-dopa without motor fluctuations or dyskinesias. However, there have been many papers on patients with a wide range of features, which report them as DRD mainly because they had dystonic syndromes with L-dopa responsiveness. Many mutations in the dopaminergic system have been found as molecular genetic defects. Therefore, the clinical and genetic spectra of DRD are unclear, which lead to difficulties in diagnostic work-ups and planning treatments. We propose the concept of DRD and DRD-plus to clarify the confusion in this area and to help understand the pathophysiology and clinical features, which will help in guiding diagnostic investigations and planning treatments. We critically reviewed the literature on atypical cases and discussed the limitations of the gene study.
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Affiliation(s)
- Woong-Woo Lee
- Movement Disorder Center, CRI, Seoul National University Hospital, Seoul, Korea
- Department of Neurology, College of Medicine, Seoul National University, Seoul, Korea
| | - Beom Seok Jeon
- Movement Disorder Center, CRI, Seoul National University Hospital, Seoul, Korea
- Department of Neurology, College of Medicine, Seoul National University, Seoul, Korea
- Department of Neurology, Seoul National University Hospital, Seoul, Korea
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Abstract
Background. The diagnosis of autosomal dominant GTP-cyclohydrolase deficiency relies on the examination of the GCH1 gene and/or pterins and neurotransmitters in CSF. The aim of the study was to assess the diagnostic value, if any, of pterins in urine and blood phenylalanine (Phe) and tyrosine (Tyr) under oral Phe loading test. Methods. We report on two new pedigrees with four symptomatic and four asymptomatic carriers whose pattern of urinary pterins and blood Phe/Tyr ratio under oral Phe loading pointed to GTP-cyclohydrolase deficiency. The study was then extended to 3 further patients and 90 controls. The diagnostic specificity and sensitivity of these metabolic markers were analysed by backwards logistic analysis. Results. Two genetic alterations segregated alternatively in Family 1 (c.631-632 del AT and c.671A > G), while exon 1 deletion was transmitted along three generations in Family 2. Neopterin and biopterin concentrations in urine clustered differently in controls under and over the age of 15. Therefore patients and controls were sub grouped according to this age. Neopterin was significantly reduced in GCH1 mutated subjects younger than 15, and both neopterin and biopterin in those older than 15. Moreover, the Phe/Tyr ratios at the second and third hour were both significantly higher in patients than in controls. Backwards logistic regression demonstrated the high diagnostic sensitivity and specificity of combined values of neopterin concentration and Phe/Tyr ratio at the second hour. Conclusions. Pterins in urine and Phe loading test are non-invasive and reliable tools for the biochemical diagnosis of GTP-cyclohydrolase deficiency.
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Albanese A, Asmus F, Bhatia KP, Elia AE, Elibol B, Filippini G, Gasser T, Krauss JK, Nardocci N, Newton A, Valls-Solé J. EFNS guidelines on diagnosis and treatment of primary dystonias. Eur J Neurol 2011; 18:5-18. [PMID: 20482602 DOI: 10.1111/j.1468-1331.2010.03042.x] [Citation(s) in RCA: 258] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
OBJECTIVES to provide a revised version of earlier guidelines published in 2006. BACKGROUND primary dystonias are chronic and often disabling conditions with a widespread spectrum mainly in young people. DIAGNOSIS primary dystonias are classified as pure dystonia, dystonia plus or paroxysmal dystonia syndromes. Assessment should be performed using a validated rating scale for dystonia. Genetic testing may be performed after establishing the clinical diagnosis. DYT1 testing is recommended for patients with primary dystonia with limb onset before age 30, and in those with an affected relative with early-onset dystonia. DYT6 testing is recommended in early-onset or familial cases with cranio-cervical dystonia or after exclusion of DYT1. Individuals with early-onset myoclonus should be tested for mutations in the DYT11 gene. If direct sequencing of the DYT11 gene is negative, additional gene dosage is required to improve the proportion of mutations detected. A levodopa trial is warranted in every patient with early-onset primary dystonia without an alternative diagnosis. In patients with idiopathic dystonia, neurophysiological tests can help with describing the pathophysiological mechanisms underlying the disorder. TREATMENT botulinum toxin (BoNT) type A is the first-line treatment for primary cranial (excluding oromandibular) or cervical dystonia; it is also effective on writing dystonia. BoNT/B is not inferior to BoNT/A in cervical dystonia. Pallidal deep brain stimulation (DBS) is considered a good option, particularly for primary generalized or cervical dystonia, after medication or BoNT have failed. DBS is less effective in secondary dystonia. This treatment requires a specialized expertise and a multidisciplinary team.
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Affiliation(s)
- A Albanese
- Istituto Neurologico Carlo Besta, Milan, Italy Università Cattolica del Sacro Cuore, Milan, Italy.
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Albanese A, Barnes MP, Bhatia KP, Fernandez-Alvarez E, Filippini G, Gasser T, Krauss JK, Newton A, Rektor I, Savoiardo M, Valls-Solè J. A systematic review on the diagnosis and treatment of primary (idiopathic) dystonia and dystonia plus syndromes: report of an EFNS/MDS-ES Task Force. Eur J Neurol 2006; 13:433-44. [PMID: 16722965 DOI: 10.1111/j.1468-1331.2006.01537.x] [Citation(s) in RCA: 219] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
To review the literature on primary dystonia and dystonia plus and to provide evidence-based recommendations. Primary dystonia and dystonia plus are chronic and often disabling conditions with a widespread spectrum mainly in young people. Computerized MEDLINE and EMBASE literature reviews (1966-1967 February 2005) were conducted. The Cochrane Library was searched for relevant citations. Diagnosis and classification of dystonia are highly relevant for providing appropriate management and prognostic information, and genetic counselling. Expert observation is suggested. DYT-1 gene testing in conjunction with genetic counselling is recommended for patients with primary dystonia with onset before age 30 years and in those with an affected relative with early onset. Positive genetic testing for dystonia (e.g. DYT-1) is not sufficient to make diagnosis of dystonia. Individuals with myoclonus should be tested for the epsilon-sarcoglycan gene (DYT-11). A levodopa trial is warranted in every patient with early onset dystonia without an alternative diagnosis. Brain imaging is not routinely required when there is a confident diagnosis of primary dystonia in adult patients, whereas it is necessary in the paediatric population. Botulinum toxin (BoNT) type A (or type B if there is resistance to type A) can be regarded as first line treatment for primary cranial (excluding oromandibular) or cervical dystonia and can be effective in writing dystonia. Actual evidence is lacking on direct comparison of the clinical efficacy and safety of BoNT-A vs. BoNT-B. Pallidal deep brain stimulation (DBS) is considered a good option, particularly for generalized or cervical dystonia, after medication or BoNT have failed to provide adequate improvement. Selective peripheral denervation is a safe procedure that is indicated exclusively in cervical dystonia. Intrathecal baclofen can be indicated in patients where secondary dystonia is combined with spasticity. The absolute and comparative efficacy and tolerability of drugs in dystonia, including anticholinergic and antidopaminergic drugs, is poorly documented and no evidence-based recommendations can be made to guide prescribing.
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Affiliation(s)
- A Albanese
- Istituto Nazionale Neurologico Carlo Besta, Milan, Italy.
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7
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López-Laso E, Ormazabal A, Camino R, Gascón FJ, Ochoa JJ, Mateos ME, Muñoz MJ, Pérez-Navero JL, Lao JI, Vilaseca MA, Artuch R. Oral phenylalanine loading test for the diagnosis of dominant guanosine triphosphate cyclohydrolase 1 deficiency. Clin Biochem 2006; 39:893-7. [PMID: 16624273 DOI: 10.1016/j.clinbiochem.2006.03.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2006] [Revised: 03/03/2006] [Accepted: 03/09/2006] [Indexed: 11/24/2022]
Abstract
OBJECTIVES To evaluate the usefulness of Phe loading test in patients for the diagnosis of guanosine triphosphate cyclohydrolase 1 deficiency (GTPCH). DESIGN AND METHODS We studied one family composed of 13 members harbouring the Q89X mutation in the GTPCH gene, a non-related pediatric patient with GTPCH deficiency and 8 pediatric controls. 100 mg/kg of L-phenylalanine was orally administered, and blood spot samples were taken at baselines 1, 2, 4 and 6 h post-load. RESULTS Two out of 7 pediatric patients showed a phenylalanine/tyrosine ratio higher than the previously reported cut-off value of 5.25 at 4 h, while 6 of the 7 adult patients showed a higher value. The only adult patient with a phenylalanine/tyrosine ratio below 5.25 at 4 h was asymptomatic. CONCLUSIONS A cut-off value of 5.25 seems reliable for interpreting Phe loading test in adult patients with GTPCH deficiency, although a lower value should be established for pediatric patients.
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Affiliation(s)
- Eduardo López-Laso
- Department of Paediatrics, Hospital Universitario Reina Sofía, Córdoba, Spain
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8
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Saunders-Pullman R, Blau N, Hyland K, Zschocke J, Nygaard T, Raymond D, Shanker V, Mohrmann K, Arnold L, Tabbal S, deLeon D, Ford B, Brin M, Chouinard S, Ozelius L, Klein C, Bressman SB. Phenylalanine loading as a diagnostic test for DRD: interpreting the utility of the test. Mol Genet Metab 2004; 83:207-12. [PMID: 15542391 DOI: 10.1016/j.ymgme.2004.07.010] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/27/2004] [Revised: 07/15/2004] [Accepted: 07/19/2004] [Indexed: 11/28/2022]
Abstract
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.
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9
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Abstract
The pediatric neurotransmitter disorders represent a challenging group of rare neurometabolic disorders classified on the basis of alterations in neurotransmitter metabolic pathways. The disorders are currently classified into disturbances of monoamine and gamma-aminobutyric acid (GABA) metabolism, although disorders of other neurotransmitters, such as glutamate and melatonin, may well be recognized in future investigations. This review summarizes the clinical and laboratory features of selected pediatric neurotransmitter disorders that have been partially delineated. Of the monoamine group, these are Segawa disease or guanosine triphosphate-cyclohydrolase I deficiency, aromatic L-amino acid decarboxylase deficiency, and tyrosine hydroxylase deficiency. Of the GABA disorders, these are pyridoxine-dependent epilepsy, GABA transaminase deficiency, and succinic semialdehyde dehydrogenase deficiency. As proper collection, handling, and interpretation of cerebrospinal fluid is required for assessment of most of these disorders, we end by summarizing important considerations for obtaining cerebrospinal fluid samples.
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Affiliation(s)
- Phillip L Pearl
- Department of Neurology, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010-2970, USA.
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Hyland K, Gunasekara RS, Munk-Martin TL, Arnold LA, Engle T. The hph-1 mouse: a model for dominantly inherited GTP-cyclohydrolase deficiency. Ann Neurol 2003; 54 Suppl 6:S46-8. [PMID: 12891653 DOI: 10.1002/ana.10695] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Dominantly inherited guanosine triphosphate (GTP)-cyclohydrolase deficiency, otherwise known as Segawa's disease or dopa-responsive dystonia, has a wide spectrum of phenotypic expression ranging from asymptomatic to very severe. Penetrance is more frequent in women as compared with men, and there is a variable occurrence of diurnal variation in symptom intensity. Biochemical characterization of the disease has demonstrated lower cerebrospinal fluid levels of tetrahydrobiopterin (BH4), neopterin, and homovanillic acid and low levels of tyrosine hydroxylase protein in the striatum. To investigate the pathophysiology, we have begun to characterize biogenic amine and BH4 metabolism in the GTP cyclohydrolase deficient hph-1 mouse. The data show low brain levels of BH4, catecholamines, serotonin, and their metabolites together with low levels of tyrosine hydroxylase protein within the striatum. The hph-1 mouse therefore provides a good model system in which to study the human disease.
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Affiliation(s)
- Keith Hyland
- Institute of Metabolic Disease, Baylor University Medical Center, Dallas, TX 75226, USA.
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Abstract
The investigation of infants and children with suspected pediatric neurotransmitter diseases affecting serotonin and catecholamine metabolism is complicated because the measurement of metabolites in peripheral fluids is generally uninformative. Disorders that affect catecholamine (dopamine and norepinephrine) and serotonin neurotransmission, and that do not present with hyperphenylalaninemia, require that a lumbar puncture be performed and that specific metabolites be assessed in the collected cerebrospinal fluid. This review will discuss the disorders affecting catecholamine and serotonin biosynthesis, sample collection and handling, diagnostic methods and expected profiles, problems with diagnosis, and as yet to be described conditions that might be detected using current diagnostic methodologies.
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Affiliation(s)
- Keith Hyland
- Institute of Metabolic Disease, Dallas, TX 75229, USA.
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Blau N, Bonafé L, Thöny B. Tetrahydrobiopterin deficiencies without hyperphenylalaninemia: diagnosis and genetics of dopa-responsive dystonia and sepiapterin reductase deficiency. Mol Genet Metab 2001; 74:172-85. [PMID: 11592814 DOI: 10.1006/mgme.2001.3213] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
DOPA responsive dystonia (DRD) and sepiapterin reductase (SR) deficiency are inherited disorders of tetrahydrobiopterin (BH4) metabolism characterized by the signs and symptoms related to monoamine neurotransmitter deficiency. In contrast to classical forms of BH4 deficiency DRD and SR deficiency present without hyperphenylalaninemia and thus cannot be detected by the neonatal screening for phenylketonuria (PKU). While DRD is mostly caused by autosomal dominant mutations in the GTP cyclohydrolase I gene (GCH1), SR deficiency is an autosomal recessive disease. The most important biochemical investigations for the diagnosis of these neurological diseases includes CSF investigations for neurotransmitter metabolites and pterins as well as neopterin and biopterin production in cytokine-stimulated fibroblasts. Discovery of SR deficiency opened new insights into alternative pathways of the cofactor BH4 via carbonyl, aldose, and dihydrofolate reductases. As a consequence of the low dihydrofolate reductase activity in the brain, dihydrobiopterin intermediate accumulates and inhibits tyrosine and tryptophan hydroxylases and uncouples nitric oxide synthase (nNOS), leading to neurotransmitter deficiency and possibly also to neuronal cell death.
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Affiliation(s)
- N Blau
- Division of Clinical Chemistry and Biochemistry, University Children's Hospital, Steinwiesstrasse 75, Zurich, 8032, Switzerland.
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