Biomaterial Database

Phenylketonuria: tyrosine supplementation in phenylalanine-restricted diets. 2001

F J van Spronsen, and M van Rijn, and J Bekhof, and R Koch, and P G Smit

Department of Metabolic Diseases, Beatrix Children's Hospital, University Hospital of Groningen, The Netherlands. f.j.van.spronsen@bkk.azg.nl

Treatment of phenylketonuria (PKU) consists of restriction of natural protein and provision of a protein substitute that lacks phenylalanine but is enriched in tyrosine. Large and unexplained differences exist, however, in the tyrosine enrichment of the protein substitutes. Furthermore, some investigators advise providing extra free tyrosine in addition to the tyrosine-enriched protein substitute, especially in the treatment of maternal PKU. In this article, we discuss tyrosine concentrations in blood during low-phenylalanine, tyrosine-enriched diets and the implications of these blood tyrosine concentrations for supplementation with tyrosine. We conclude that the present method of tyrosine supplementation during the day is far from optimal because it does not prevent low blood tyrosine concentrations, especially after an overnight fast, and may result in largely increased blood tyrosine concentrations during the rest of the day. Both high tyrosine enrichment of protein substitutes and extra free tyrosine supplementation may not be as safe as considered at present, especially to the fetus of a woman with PKU. The development of dietary compounds that release tyrosine more slowly could be beneficial. We advocate decreasing the tyrosine content of protein substitutes to approximately 6% by wt (6 g/100 g protein equivalent) at most and not giving extra free tyrosine without knowing the diurnal variations in the blood tyrosine concentration and having biochemical evidence of a tyrosine deficiency. We further advocate that a better daily distribution of the protein substitute be achieved by improving the palatability of these products.

UI	MeSH Term	Description	Entries
D008431	Maternal-Fetal Exchange	Exchange of substances between the maternal blood and the fetal blood at the PLACENTA via PLACENTAL CIRCULATION. The placental barrier excludes microbial or viral transmission.	Transplacental Exposure,Exchange, Maternal-Fetal,Exposure, Transplacental,Maternal Fetal Exchange
D010649	Phenylalanine	An essential aromatic amino acid that is a precursor of MELANIN; DOPAMINE; noradrenalin (NOREPINEPHRINE), and THYROXINE.	Endorphenyl,L-Phenylalanine,Phenylalanine, L-Isomer,L-Isomer Phenylalanine,Phenylalanine, L Isomer
D010661	Phenylketonurias	A group of autosomal recessive disorders marked by a deficiency of the hepatic enzyme PHENYLALANINE HYDROXYLASE or less frequently by reduced activity of DIHYDROPTERIDINE REDUCTASE (i.e., atypical phenylketonuria). Classical phenylketonuria is caused by a severe deficiency of phenylalanine hydroxylase and presents in infancy with developmental delay; SEIZURES; skin HYPOPIGMENTATION; ECZEMA; and demyelination in the central nervous system. (From Adams et al., Principles of Neurology, 6th ed, p952).	Biopterin Deficiency,Dihydropteridine Reductase Deficiency Disease,Hyperphenylalaninemia, Non-Phenylketonuric,Phenylalanine Hydroxylase Deficiency Disease,BH4 Deficiency,DHPR Deficiency,Deficiency Disease, Dihydropteridine Reductase,Deficiency Disease, Phenylalanine Hydroxylase,Deficiency Disease, Phenylalanine Hydroxylase, Severe,Dihydropteridine Reductase Deficiency,Folling Disease,Folling's Disease,HPABH4C,Hyperphenylalaninaemia,Hyperphenylalaninemia Caused by a Defect in Biopterin Metabolism,Hyperphenylalaninemia, BH4-Deficient, C,Hyperphenylalaninemia, Tetrahydrobiopterin-Deficient, Due To DHPR Deficiency,Non-Phenylketonuric Hyperphenylalaninemia,Oligophrenia Phenylpyruvica,PAH Deficiency,PKU, Atypical,Phenylalanine Hydroxylase Deficiency,Phenylalanine Hydroxylase Deficiency Disease, Severe,Phenylketonuria,Phenylketonuria I,Phenylketonuria II,Phenylketonuria Type 2,Phenylketonuria, Atypical,Phenylketonuria, Classical,QDPR Deficiency,Quinoid Dihydropteridine Reductase Deficiency,Tetrahydrobiopterin Deficiency,Atypical PKU,Atypical Phenylketonuria,Biopterin Deficiencies,Classical Phenylketonuria,Deficiency, BH4,Deficiency, Biopterin,Deficiency, DHPR,Deficiency, Dihydropteridine Reductase,Deficiency, PAH,Deficiency, Phenylalanine Hydroxylase,Deficiency, QDPR,Deficiency, Tetrahydrobiopterin,Disease, Folling,Disease, Folling's,Hyperphenylalaninemia, Non Phenylketonuric,Non Phenylketonuric Hyperphenylalaninemia,Non-Phenylketonuric Hyperphenylalaninemias
D011247	Pregnancy	The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH.	Gestation,Pregnancies
D011248	Pregnancy Complications	Conditions or pathological processes associated with pregnancy. They can occur during or after pregnancy, and range from minor discomforts to serious diseases that require medical interventions. They include diseases in pregnant females, and pregnancies in females with diseases.	Adverse Birth Outcomes,Complications, Pregnancy,Adverse Birth Outcome,Birth Outcome, Adverse,Complication, Pregnancy,Outcome, Adverse Birth,Pregnancy Complication
D002940	Circadian Rhythm	The regular recurrence, in cycles of about 24 hours, of biological processes or activities, such as sensitivity to drugs or environmental and physiological stimuli.	Diurnal Rhythm,Nyctohemeral Rhythm,Twenty-Four Hour Rhythm,Nycthemeral Rhythm,Circadian Rhythms,Diurnal Rhythms,Nycthemeral Rhythms,Nyctohemeral Rhythms,Rhythm, Circadian,Rhythm, Diurnal,Rhythm, Nycthemeral,Rhythm, Nyctohemeral,Rhythm, Twenty-Four Hour,Rhythms, Circadian,Rhythms, Diurnal,Rhythms, Nycthemeral,Rhythms, Nyctohemeral,Rhythms, Twenty-Four Hour,Twenty Four Hour Rhythm,Twenty-Four Hour Rhythms
D004032	Diet	Regular course of eating and drinking adopted by a person or animal.	Diets
D004305	Dose-Response Relationship, Drug	The relationship between the dose of an administered drug and the response of the organism to the drug.	Dose Response Relationship, Drug,Dose-Response Relationships, Drug,Drug Dose-Response Relationship,Drug Dose-Response Relationships,Relationship, Drug Dose-Response,Relationships, Drug Dose-Response
D005260	Female		Females
D005527	Food, Fortified	Any food that has been supplemented with essential NUTRIENTS either in quantities that are greater than those normally present, or which are not found in the food typically. Fortified food also includes food enriched by adding various nutrients to compensate for those removed by refinement or processing. (Modified from Segen, Dictionary of Modern Medicine, 1992).	Enriched Food,Food, Supplemented,Enriched Foods,Food, Enriched,Foods, Enriched,Foods, Fortified,Foods, Supplemented,Fortified Food,Fortified Foods,Supplemented Food,Supplemented Foods