Growth, nutrient intake and plasma phenylalanine and tyrosine concentrations of infants treated with phenex TM-1 amino acid modified medical food with iron

Abstract

The objective of this study was to evaluate the effects of a new medical food (Phenex-1) on growth, nutrient intake and plasma phenylalanine (PHE) and tyrosine (TYR) concentrations of infants and toddlers with phenylketonuria (PKU). Ten full-term infants (5F, 5M) with classical PKU were placed on Phenex-1 as their primary protein source at a mean age of 11.8 days (range 7–20 days). Two infants received human milk and eight received proprietary infant formula as the source of PHE. Anthropometric measures were obtained by standard techniques, nutrient intakes were calculated using Amino Acid Analyzer© software, and plasma amino acids were analyzed by ion exchange chromatography. When compared to NCHS growth curves, mean head circumference and weight of subjects at birth were at the 75th percentile and greater than the 75th percentile at six months of age. Mean length was at the 75th percentile at birth and at six months of age. During the first three months of study mean PHE intake was 47 mg/kg (range 34–67 mg/kg) and mean TYR intake was 154 mg/kg (range 119–291 mg/kg). During the second three months of study mean PHE intake was 36 mg/kg (range 27–61 mg/kg) and mean TYR intake was 214 mg/kg (range 181–257 mg/kg). Mean protein intake during the study was consistently above RDAs; mean energy intake, except at month one, was below RDAs and the lowest mean value was 87% of RDA at 3 months of age. Mean plasma PHE (35 samples) during the course of the study was 258 μmol/L (range 6–1054 μmol/L) (NL 19–76 μmol/L). Twenty-three percent of samples were in the normal range; forty percent were < 121 μmol/L, 66% were < 303 μmol/L and 89% of samples were < 619 μmol/L. Mean plasma TYR was 47 μmol/L (range 16–98 μmol/L) (NL 25–148 μmol/L). Ninety-one percent of the 35 plasma TYR concentrations were in the normal range. Despite energy intakes that were below RDAs and plasma PHE that was < 121 μmol/L in 40% of the samples, Phenex-1 supported excellent growth and normal plasma TYR concentrations.