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Abstract
BACKGROUND Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap. However, the diet is very restrictive and unpalatable and can be difficult to follow. A deficiency of the amino acid tyrosine has been suggested as a cause of some of the neuropsychological problems exhibited in phenylketonuria. Therefore, this review aims to assess the efficacy of tyrosine supplementation for phenylketonuria. This is an update of previously published versions of this review. OBJECTIVES To assess the effects of tyrosine supplementation alongside or instead of a phenylalanine-restricted diet for people with phenylketonuria, who commenced on diet at diagnosis and either continued on the diet or relaxed the diet later in life. To assess the evidence that tyrosine supplementation alongside, or instead of a phenylalanine-restricted diet improves intelligence, neuropsychological performance, growth and nutritional status, mortality rate and quality of life. SEARCH METHODS We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register which is comprised of references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings. Additional studies were identified from handsearches of the Journal of Inherited Metabolic Disease (from inception in 1978 to 1998). The manufacturers of prescribable dietary products used in the treatment of phenylketonuria were also contacted for further references. Date of the most recent search of the Group's Inborn Errors of Metabolism Trials Register: 07 December 2020. SELECTION CRITERIA All randomised or quasi-randomised trials investigating the use of tyrosine supplementation versus placebo in people with phenylketonuria in addition to, or instead of, a phenylalanine-restricted diet. People treated for maternal phenylketonuria were excluded. DATA COLLECTION AND ANALYSIS Two authors independently assessed the trial eligibility, methodological quality and extracted the data. MAIN RESULTS Six trials were found, of which three trials reporting the results of a total of 56 participants, were suitable for inclusion in the review. The blood tyrosine concentrations were significantly higher in the participants receiving tyrosine supplements than those in the placebo group, mean difference 23.46 (95% confidence interval 12.87 to 34.05). No significant differences were found between any of the other outcomes measured. The trials were assessed as having a low to moderate risk of bias across several domains. AUTHORS' CONCLUSIONS From the available evidence no recommendations can be made about whether tyrosine supplementation should be introduced into routine clinical practice. Further randomised controlled studies are required to provide more evidence. However, given this is not an active area of research, we have no plans to update this review in the future.
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Affiliation(s)
- Tracey Remmington
- Department of Women's and Children's Health, University of Liverpool, Liverpool, UK
| | - Sherie Smith
- Division of Child Health, Obstetrics & Gynaecology (COG), School of Medicine, University of Nottingham, Nottingham, UK
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Montoya Parra GA, Singh RH, Cetinyurek-Yavuz A, Kuhn M, MacDonald A. Status of nutrients important in brain function in phenylketonuria: a systematic review and meta-analysis. Orphanet J Rare Dis 2018; 13:101. [PMID: 29941009 PMCID: PMC6020171 DOI: 10.1186/s13023-018-0839-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 06/05/2018] [Indexed: 01/08/2023] Open
Abstract
Background Despite early and ongoing dietary management with a phe-restricted diet, suboptimal neuropsychological function has been observed in PKU. The restrictive nature of the PKU diet may expose patients to sub-optimal nutritional intake and deficiencies which may impact normal brain function. A systematic review of the published literature was carried out, where possible with meta-analysis, to compare the status of nutrients (Nutrients: DHA, EPA phospholipids, selenium, vitamins B6, B12, E, C, A, D, folic acid, choline, uridine, calcium, magnesium, zinc, iron, iodine and cholesterol) known to be important for brain development and functioning between individuals with PKU and healthy controls. Results Of 1534 publications identified, 65 studies met the entry criteria. Significantly lower levels of DHA, EPA and cholesterol were found for PKU patients compared to healthy controls. No significant differences in zinc, vitamins B12, E and D, calcium, iron and magnesium were found between PKU patients and controls. Because of considerable heterogeneity, the meta-analyses findings for folate and selenium were not reported. Due to an insufficient number of publications (< 4) no meta-analysis was undertaken for vitamins A, C and B6, choline, uridine, iodine and phospholipids. Conclusions The current data show that PKU patients have lower availability of DHA, EPA and cholesterol. Compliance with the phe-restricted diet including the micronutrient fortified protein substitute (PS) is essential to ensure adequate micronutrient status. Given the complexity of the diet, patients’ micronutrient and fatty acid status should be continuously monitored, with a particular focus on patients who are non-compliant or poorly compliant with their PS. Given their key role in brain function, assessment of the status of nutrients where limited data was found (e.g. choline, iodine) should be undertaken. Standardised reporting of studies in PKU would strengthen the output of meta-analysis and so better inform best practice for this rare condition. Electronic supplementary material The online version of this article (10.1186/s13023-018-0839-x) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Gina A Montoya Parra
- Danone Nutricia Research, Nutricia Advanced Medical Nutrition, Utrecht, The Netherlands.
| | - Rani H Singh
- Metabolic Genetics and Nutrition Program, Emory University, Atlanta, GA, USA
| | | | - Mirjam Kuhn
- Danone Nutricia Research, Nutricia Advanced Medical Nutrition, Utrecht, The Netherlands
| | - Anita MacDonald
- Department of Metabolic Diseases, Birmingham Children's Hospital, Birmingham, UK
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Preissler T, Bristot IJ, Costa BML, Fernandes EK, Rieger E, Bortoluzzi VT, de Franceschi ID, Dutra-Filho CS, Moreira JCF, Wannmacher CMD. Phenylalanine induces oxidative stress and decreases the viability of rat astrocytes: possible relevance for the pathophysiology of neurodegeneration in phenylketonuria. Metab Brain Dis 2016; 31:529-37. [PMID: 26573865 DOI: 10.1007/s11011-015-9763-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 11/09/2015] [Indexed: 01/05/2023]
Abstract
The aim of this study was to investigate the effects of phenylalanine on oxidative stress and some metabolic parameters in astrocyte cultures from newborn Wistar rats. Astrocytes were cultured under four conditions: control (0.4 mM phenylalanine concentration in the Dulbecco's Modified Eagle Medium (DMEM) solution), Phe addition to achieve 0.5, 1.0 or 1.5 mM final phenylalanine concentrations. After 72 h the astrocytes were separated for the biochemical measurements. Overall measure of mitochondrial function by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and cell viability measured by lactate dehydrogenase (LDH) assays indicated that phenylalanine induced cell damage at the three concentrations tested. The alteration on the various parameters of oxidative stress indicated that phenylalanine was able to induce free radicals production. Therefore, our results strongly suggest that Phe at concentrations usually found in PKU induces oxidative stress and consequently cell death in astrocytes cultures. Considering the importance of the astrocytes for brain function, it is possible that these astrocytes alterations may contribute to the brain damage found in PKU patients.
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Affiliation(s)
- Thales Preissler
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - Ivi Juliana Bristot
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - Bruna May Lopes Costa
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - Elissa Kerli Fernandes
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - Elenara Rieger
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - Vanessa Trindade Bortoluzzi
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - Itiane Diehl de Franceschi
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - Carlos Severo Dutra-Filho
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - José Claudio Fonseca Moreira
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil
| | - Clovis Milton Duval Wannmacher
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo, CEP, Porto Alegre, RS, 90035-003, Brazil.
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Singh RH, Cunningham AC, Mofidi S, Douglas TD, Frazier DM, Hook DG, Jeffers L, McCune H, Moseley KD, Ogata B, Pendyal S, Skrabal J, Splett PL, Stembridge A, Wessel A, Rohr F. Updated, web-based nutrition management guideline for PKU: An evidence and consensus based approach. Mol Genet Metab 2016; 118:72-83. [PMID: 27211276 DOI: 10.1016/j.ymgme.2016.04.008] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Revised: 04/15/2016] [Accepted: 04/15/2016] [Indexed: 10/21/2022]
Abstract
BACKGROUND In 2014, recommendations for the nutrition management of phenylalanine hydroxylase deficiency were published as a companion to the concurrently published American College of Medical Genetics and Genomics guideline for the medical treatment of phenylketonuria (PKU). These were developed primarily from a summary of findings from the PKU scientific review conference sponsored by the National Institutes of Health and Agency for Healthcare Research & Quality along with additional systematic literature review. Since that time, the Genetic Metabolic Dietitians International and the Southeast Regional Newborn Screening and Genetics Collaborative have partnered to create a web-based technology platform for the update and development of nutrition management guidelines for inherited metabolic disorders. OBJECTIVE The purpose of this PKU guideline is to establish harmonization in treatment and monitoring, to guide the integration of nutrition therapy in the medical management of PKU, and to improve outcomes (nutritional, cognitive, and developmental) for individuals with PKU in all life stages while reducing associated medical, educational, and social costs. METHODS Six research questions critical to PKU nutrition management were formulated to support guideline development: Review, critical appraisal, and abstraction of peer-reviewed studies and unpublished practice literature, along with expert Delphi survey feedback, nominal group process, and external review from metabolic physicians and dietitians were utilized for development of recommendations relevant to each question. Recommendations address nutrient intake, including updated protein requirements, optimal blood phenylalanine concentrations, nutrition interventions, monitoring parameters specific to life stages, adjunct therapies, and pregnancy and lactation. Recommendations were graded using a rigorous system derived from the Academy of Nutrition and Dietetics. RESULTS AND CONCLUSION These guidelines, updated utilizing a thorough and systematic approach to literature analysis and national consensus process, are now easily accessible to the global community via the newly developed digital platform. For additional details on specific topics, readers are encouraged to review materials on the online portal: https://GMDI.org/.
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Affiliation(s)
- Rani H Singh
- Department of Human Genetics, Emory University School of Medicine, 2165 North Decatur Road, Decatur, Atlanta, GA 30033, USA; Nutrition Health Sciences Program, Graduate Division of Biological and Biomedical Sciences, Emory University School of Arts and Sciences, Atlanta, GA, USA.
| | - Amy C Cunningham
- Hayward Genetics Center, Tulane University School of Medicine, 1430 Tulane Ave, New Orleans, LA 70112, USA.
| | - Shideh Mofidi
- Inherited Metabolic Disease Center, Maria Fareri Childrens Hospital, Westchester Medical Center, New York Medical College, Valhalla, New York, USA.
| | - Teresa D Douglas
- Department of Human Genetics, Emory University School of Medicine, 2165 North Decatur Road, Decatur, Atlanta, GA 30033, USA.
| | - Dianne M Frazier
- Division of Genetics and Metabolism, University of North Carolina School of Medicine, 1100 Manning Drive, Chapel Hill, NC 27599, USA.
| | | | - Laura Jeffers
- Cleveland Clinic, Center for Human Nutrition, 9500 Euclid Ave, Cleveland, OH 44195, USA.
| | - Helen McCune
- Pediatric Genetics and Metabolism, University of Florida, 1600 SW Archer Rd, Gainesville, FL 32607, USA.
| | - Kathryn D Moseley
- Genetics Division, USC/Keck School of Medicine, 1801 Marengo St. Rm. 1G-24, Los Angeles, CA 90033, USA.
| | - Beth Ogata
- University of Washington, Department of Pediatrics, UW-CHDD, Box 357920, Seattle, WA 98195, USA.
| | - Surekha Pendyal
- Division of Genetics and Metabolism, University of North Carolina School of Medicine, 1100 Manning Drive, Chapel Hill, NC 27599, USA.
| | - Jill Skrabal
- Department of Medical Genetics, University of Nebraska Medical Center/Children's Hospital and Medical Center, 981200 Nebraska Medical Center, Omaha, NE. 68198-1200, USA.
| | - Patricia L Splett
- Evaluation Consultant Splett & Associates, LLC, 399 Badger Blvd W., Stanchfield, MN 55080, USA.
| | - Adrya Stembridge
- Department of Human Genetics, Emory University School of Medicine, 2165 North Decatur Road, Decatur, Atlanta, GA 30033, USA.
| | - Ann Wessel
- Division of Genetics and Genomics, Boston Children's Hospital, 300 Longwood Ave, Boston, MA 02115, USA.
| | - Frances Rohr
- Division of Genetics and Genomics, Boston Children's Hospital, 300 Longwood Ave, Boston, MA 02115, USA.
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Abstract
BACKGROUND Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap. However, the diet is very restrictive and unpalatable and can be difficult to follow. A deficiency of the amino acid tyrosine has been suggested as a cause of some of the neuropsychological problems exhibited in phenylketonuria. Therefore, this review aims to assess the efficacy of tyrosine supplementation for phenylketonuria. OBJECTIVES To assess the effects of tyrosine supplementation alongside or instead of a phenylalanine-restricted diet for people with phenylketonuria, who commenced on diet at diagnosis and either continued on the diet or relaxed the diet later in life. To assess the evidence that tyrosine supplementation alongside, or instead of a phenylalanine-restricted diet improves intelligence, neuropsychological performance, growth and nutritional status, mortality rate and quality of life. SEARCH METHODS We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register which is comprised of references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings. Additional studies were identified from handsearches of the Journal of Inherited Metabolic Disease (from inception in 1978 to 1998). The manufacturers of prescribable dietary products used in the treatment of phenylketonuria were also contacted for further references.Date of the most recent search of the Group's Inborn Errors of Metabolism Trials Register: 28 June 2012. SELECTION CRITERIA All randomised or quasi-randomised trials investigating the use of tyrosine supplementation versus placebo in people with phenylketonuria in addition to, or instead of, a phenylalanine-restricted diet. People treated for maternal phenylketonuria were excluded. DATA COLLECTION AND ANALYSIS Two authors independently assessed the trial eligibility, methodological quality and extracted the data. MAIN RESULTS Six trials were found, of which three trials reporting the results of a total of 56 participants, were suitable for inclusion in the review. The blood tyrosine concentrations were significantly higher in the participants receiving tyrosine supplements than those in the placebo group, mean difference 23.46 (95% confidence interval 12.87 to 34.05). No significant differences were found between any of the other outcomes measured. AUTHORS' CONCLUSIONS From the available evidence no recommendations can be made about whether tyrosine supplementation should be introduced into routine clinical practice. Further randomised controlled studies are required to provide more evidence.
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Affiliation(s)
- Diana Webster
- Nutrition and Dietetic Department, Bristol Royal Hospital for Children, Bristol, UK.
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Nasser M, Javaheri H, Fedorowicz Z, Noorani Z. Carnitine supplementation for inborn errors of metabolism. Cochrane Database Syst Rev 2012; 2012:CD006659. [PMID: 22336821 PMCID: PMC7390060 DOI: 10.1002/14651858.cd006659.pub3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND Inborn errors of metabolism are genetic conditions which can lead to abnormalities in the synthesis and metabolism of proteins, carbohydrates, or fats. It has been proposed that in some instances carnitine supplementation should be provided to infants with a suspected metabolic disease as an interim measure, particularly whilst awaiting test results. Carnitine supplementation is used in the treatment of primary carnitine deficiency, and also where the deficiency is a secondary complication of several inborn errors of metabolism, such as organic acidaemias and fatty acid oxidation defects in children and adults. OBJECTIVES To assess the effectiveness and safety of carnitine supplementation in the treatment of inborn errors of metabolism. SEARCH METHODS We searched the Cystic Fibrosis and Genetic Disorders Group's Inborn Errors of Metabolism Trials Register, the Cochrane Central Register of Controlled Trials (The Cochrane Library 2007, Issue 4) and MEDLINE via Ovid (1950 to July week 4 2007), LILACS (15/05/2008) and Iranmedex (15/05/2008) and also the reference lists of retrieved articles.Date of most recent search of the Group's Inborn Errors of Metabolism Register: 27 October 2011. SELECTION CRITERIA Randomised controlled trials and quasi-randomised controlled trials comparing carnitine supplementation (in different dose, frequency, or duration) versus placebo in children and adults diagnosed with an inborn error of metabolism. DATA COLLECTION AND ANALYSIS Two authors independently screened and assessed the eligibility of the identified trials. MAIN RESULTS No trials were included in the review. AUTHORS' CONCLUSIONS There are no published or ongoing randomised controlled clinical trials relevant to this review question. Therefore, in the absence of any high level evidence, clinicians should base their decisions on clinical experience and in conjunction with preferences of the individual where appropriate. This does not mean that carnitine is ineffective or should not be used in any inborn error of metabolism. However, given the lack of evidence both on the effectiveness and safety of carnitine and on the necessary dose and frequency to be prescribed, the current prescribing practice should continue to be observed and monitored with care until further evidence is available. Methodologically sound trials, reported according to the Consolidated Standards of Reporting Trials (CONSORT) statement, are required. It should be considered whether placebo-controlled trials in potentially lethal diseases, e.g. carnitine transporter disorder or glutaric aciduria type I, are ethical.
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Affiliation(s)
- Mona Nasser
- Peninsula Dental School, University of Plymouth, Plymouth,
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Abstract
Phenylalanine hydroxylase deficiency is an autosomal recessive disorder that results in intolerance to the dietary intake of the essential amino acid phenylalanine. It occurs in approximately 1:15,000 individuals. Deficiency of this enzyme produces a spectrum of disorders including classic phenylketonuria, mild phenylketonuria, and mild hyperphenylalaninemia. Classic phenylketonuria is caused by a complete or near-complete deficiency of phenylalanine hydroxylase activity and without dietary restriction of phenylalanine most children will develop profound and irreversible intellectual disability. Mild phenylketonuria and mild hyperphenylalaninemia are associated with lower risk of impaired cognitive development in the absence of treatment. Phenylalanine hydroxylase deficiency can be diagnosed by newborn screening based on detection of the presence of hyperphenylalaninemia using the Guthrie microbial inhibition assay or other assays on a blood spot obtained from a heel prick. Since the introduction of newborn screening, the major neurologic consequences of hyperphenylalaninemia have been largely eradicated. Affected individuals can lead normal lives. However, recent data suggest that homeostasis is not fully restored with current therapy. Treated individuals have a higher incidence of neuropsychological problems. The mainstay of treatment for hyperphenylalaninemia involves a low-protein diet and use of a phenylalanine-free medical formula. This treatment must commence as soon as possible after birth and should continue for life. Regular monitoring of plasma phenylalanine and tyrosine concentrations is necessary. Targets of plasma phenylalanine of 120-360 μmol/L (2-6 mg/dL) in the first decade of life are essential for optimal outcome. Phenylalanine targets in adolescence and adulthood are less clear. A significant proportion of patients with phenylketonuria may benefit from adjuvant therapy with 6R-tetrahydrobiopterin stereoisomer. Special consideration must be given to adult women with hyperphenylalaninemia because of the teratogenic effects of phenylalanine. Women with phenylalanine hydroxylase deficiency considering pregnancy should follow special guidelines and assure adequate energy intake with the proper proportion of protein, fat, and carbohydrates to minimize risks to the developing fetus. Molecular genetic testing of the phenylalanine hydroxylase gene is available for genetic counseling purposes to determine carrier status of at-risk relatives and for prenatal testing.
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