Protein Status of Infants with Phenylketonuria Undergoing Nutrition Management

Objectives: The objectives of this study were to determine if Phenex-1, amino-acid modified medical food with iron maintained normal indices of protein status in infants with phenylketonuria (PKU) and to investigate factors that influence plasma amino acid concentrations.

Methods: A study was conducted for six months in 35 infants with classical PKU diagnosed in the neonatal period. Diet diaries and plasma amino acid concentrations were obtained monthly. Blood for analysis of plasma albumin, blood urea nitrogen (BUN), retinol binding protein (RBP) and transthyretin was obtained at one, three and six months of study.

Results: Mean (±SEM) total daily intake of medical food and nutrients was 79 ± 4 g; 17.3 ± 0.6 g protein, 660 ± 18 kcal, 255 ± 10 mg phenylalanine (Phe), and 1423 ± 56 mg tyrosine (Tyr). Mean concentrations of plasma amino acids, except cystine (during entire study), glycine (first month) and Phe were in the normal range. Mean concentrations of plasma Phe were in the treatment range (120 to 360 μmol/L). Plasma concentrations of arginine, methionine, Phe, tryptophan, Tyr, and valine were positively correlated with intakes at various months of study. Concentrations of aspartic and glutamic acids, Phe, and Tyr were positively correlated and 17 amino acids were negatively correlated with the interval between feeding and blood draw. At six months of study, concentration of plasma albumin was 4.1 ± 0.1 g/dL, RBP was 3.74 ± 0.2 mg/dL, transthyretin was 17.9 ± 0.9 mg/dL, and urea nitrogen was 11.9 ± 0.5 mg/dL.

Conclusion: During study, all mean plasma indices of protein status were in normal reference ranges. Phenex-1 supports normal mean plasma amino acid, albumin, RBP, transthyretin, and BUN concentrations when fed in adequate amounts.