Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0029713 (immaturity)
 4,335 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cause of hyperphenylalaninemia in sick preterm infants has yet to be determined; one reason may be reduced tolerance to phenylalanine as a consequence of immaturity of phenylalanine hydroxylase. Phenylalanine metabolism was studied in vivo in 23 ventilated preterm infants of gestational age 23 to 36 wk within the first 6 d of life using a continuous i.v. infusion of the stable isotope-labeled amino acids [2H5]phenylalanine, [2H4]tyrosine, and [2H2]tyrosine. Phenylalanine hydroxylation was calculated from two different methods. In the first method, used in all 23 infants receiving glucose and in seven of these infants who subsequently received parenteral nutrition, phenylalanine hydroxylation was calculated from the plasma enrichments of [2H5]phenylalanine and [2H4]tyrosine and from the molar ratio of tyrosine to phenylalanine in mammalian tissue protein. In this instance, the mean hydroxylation was 16.0 (SD 10.9) and 48.4 (SD 14.9) mumol/kg/h, which was 17.3% (SD 8.4%) and 33.2% (SD 9.8% of the total phenylalanine flux for infants receiving glucose and parenteral nutrition, respectively. Additionally, in six infants receiving glucose, hydroxylation was calculated from the measured phenylalanine (2H5), independent tyrosine (2H2) fluxes, and the plasma enrichments of (2H5) phenylalanine and its hydroxylation product [2H4]tyrosine. In this case, hydroxylation was 20.5 (SD 13.0) mumol/kg/h, which represented 22.3% (SD 9.8%) of the phenylalanine flux. In the same six infants, phenylalanine hydroxylation derived using the first method was 22.2 (SD 13.1) mumol/kg/h, 23.6% (SD 9.9%) of the total phenylalanine flux.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Phenylalanine kinetics in sick preterm neonates with respiratory distress syndrome. 789 79

To determine to what extent intravenous nutrition can reduce proteolysis in very immature and normal newborns, and to assess the capacity of preterm and normal newborns to convert phenylalanine to tyrosine, phenylalanine and leucine kinetics were measured under basal conditions and during parenteral nutrition in clinically stable, extremely premature (approximately 26 wk of gestation) infants and in normal term newborns. In response to parenteral nutrition, there was significantly less suppression (P < 0.001) of endogenous leucine and phenylalanine rate of appearance in extremely premature infants compared with term infants. Phenylalanine utilization for protein synthesis during parenteral nutrition increased significantly (P < 0.01) and by the same magnitude (approximately 15%) in both extremely premature and term infants. Phenylalanine was converted to tyrosine at substantial rates in both extremely premature and term infants; however, this conversion rate was significantly higher (P < 0.05) in extremely premature infants during both the basal and parenteral nutrition periods. These data provide clear evidence that there is no immaturity in the phenylalanine hydroxylation pathway. Furthermore, although parenteral nutrition appears to produce similar increases in protein synthesis in extremely premature and term infants, proteolysis is suppressed much less in extremely premature newborns. The factors responsible for this apparent resistance to suppression of proteolysis in the very immature newborn remain to be elucidated.
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PMID:Proteolysis and phenylalanine hydroxylation in response to parenteral nutrition in extremely premature and normal newborns. 860 31

Hyperphenylalaninemia in preterm neonates with heterozygosity for phenylketonuria has previously not been described. We report on a very low birth weight infant, born at a gestational age of 27+5 weeks with a birth weight of 1080 g. Due to a positive family history prenatal diagnosis for phenylketonuria was performed, revealing heterozygosity for classic phenylketonuria. Yet the girl showed hyperphenylalaninemia with a maximum serum phenylalanine concentration of 515 micromol/l on the eighth day of life. Phenylalanine-restrictive parenteral and enteral nutrition was kept from the eighth until the 41st day of life. At term serum phenylalanine concentrations had normalized. We hypothesize that heterozygosity for phenylketonuria may be a risk factor for hyperphenylalaninemia in preterm born infants. Prematurity and the resulting immaturity of liver function with the genetically determined reduced activity of phenylalanine hydroxylase might have caused hyperphenylalaninemia in this girl.
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PMID:Hyperphenylalaninemia in a premature infant with heterozygosity for phenylketonuria. 1534 30