Randomized controlled trial of a protein substitute with prolonged release on the protein status of children with phenylketonuria

Objective: To examine whether a phenylalanine-free protein substitute with prolonged release may be beneficial to the protein status of children with phenylketonuria (PKU) compared to conventional substitutes. Methods: Sixty children with PKU, 7 to 16 years of age, were randomly allocated to receive either a prolonged-release (test) or the current conventional protein substitute for 30 days. Subjects were additionally sex and age matched with 60 subjects with mild hyperphenylalaninemia and 60 unaffected subjects. The protein status in children with PKU was assessed by albumin, transthyretin, and retinol-binding protein (RBP), and changes throughout the trial period were the primary outcome measures. Results: Children with PKU did not differ in anthropometry from children with mild hyperphenylalaninemia or unaffected children but they ingested lower amounts of proteins (p < 0.01). No differences occurred throughout the trial between or within children with PKU who received the test or conventional substitute for macronutrient intake. Albumin and RBP concentrations were within the age-specific reference range for all children. The rate of protein insufficiency (transthyretin concentration less than 20 mg/dL) did not differ statistically between children receiving test or conventional substitute (recruitment 51.8% vs 53.6%; end of the trial 44.4% vs 50.0%) but mean transthyretin recovered over 20 mg/dL in children who received the test substitute, increasing from 19.1 to 20.7 mg/dL (mean change, 1.6 mg/dL; 95% confidence interval 0.4 to 2.8 mg/dL). In children receiving conventional substitute mean transthyretin changed from 19.0 to 19.2 mg/dL (0.2; −0.2 to 0.6) mg/dL. Conclusions: Protein substitutes with prolonged release might be beneficial to protein status in children with phenylketonuria.