Protein substitute for children and adults with phenylketonuria.

Phenylketonuria is an inherited disease characterised by an absence or deficiency of the enzyme phenylalanine hydroxylase. The aim of treatment is to lower blood phenylalanine concentrations to prevent developmental delay. Current treatment is based on a low phenylalanine diet in combination with a protein substitute (mixtures of amino acids free from or low in phenylalanine). Guidance regarding the dosage and distribution of this protein substitute, over a 24-hour period, is unclear and there is variation in recommendation between treatment centres.