Journal of the American College of Nutrition, Vol. 18, No. 2, 99 (1999)
Published by the American College of Nutrition
Protein Status of Infants with Phenylketonuria Undergoing Therapy
Kurt Widhalm, MD
Department of Pediatrics and Clinical Chemistry
University of Vienna
Vienna, Austria
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INTRODUCTION
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The amount of protein intake in infants and children that ensures optimal growth has been a matter of intense discussion during the past 20 years. Moreover, in infants and children with distinct defects of the metabolic pathway of an essential amino acid (PKU, for example), the optimal supply of protein and essential amino acid is very important not only for normal growth, but also for the development of the central nervous system, which can be negatively influenced by unbalanced amino acid intake [1]. P.P. and S. Yannicelli together with several pediatricians from ten clinics from the US and Canada conducted an important study over six months in 35 infants with classical PKU diagnosed during the neonatal period who were fed PhenexTM-1, an amino acid modified medical food with iron. This formula supplied an overall mean of 84% of RDA (2.2 g protein/kg) and 51% of RDA (115 kcal/kg) for energy. The mean concentrations of all amino acids except cystine (low), glycine (high) and phenylalanine were in the reference ranges. Sometimes the intake of Arg, Met, Phe, Trp, Tyr and valine was positively correlated with the plasma amino acid concentration. At one or more times during the study aspartic and glutamic acid, Phe and Tyr were positively correlated with the interval from the last meal to the blood draw. Seventeen amino acids were negatively correlated with time from the last meal. Interestingly, low plasma Cys levels occurred despite the intake of Cys, and Met was more than two times the minimum intake. This could be due to methodology. The main new message is the fact, that only 6% of the samples had lower levels than the recommended 120 µmol/L, and 37% had a higher than the upper limit for treatment range of 360 µmol/L.
Technical details seem to play a major role in regard to high concentrations of amino acids in the PKU patient when daily fluctuations in plasma Phe is small [2]. On the other hand, it has been agreed that for optimal treatment phenylalanine concentrations should be maintained within a narrower range than previously recommended [3]. Still, Mac Donald et al. [4] reported large intrapatient variations in Phe concentrations according to the timing of ingestion and distribution throughout the day of patients’ protein substitute. In a recently published paper, the same group reported on very large fluctuations of phe levels in a 24-hour period, however, the greater the quantity of protein substitute taken between waking and 16.00, the larger was the decrease in daytime Phe [5]. Although we do not fully understand the mechanism controlling the stability of phenylalanine with respect to the time of protein substitute, the data of Acosta et al. [1] show that PKU infants fed with Phenex exhibit surprisingly stable levels within the arbitrarily recommended range for amino acids.
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REFERENCES
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INTRODUCTION
REFERENCES
