Phenylalanine metabolites, attention span and hyperactivity.

The metabolites of phenylalanine, phenylacetate, phenyllactate, phenylpyruvate and phenylethylamine, were measured in the urine of PKU patients. In general correlation was found between serum phenylalanine excretion of these metabolites. However, there were individual variations in the quantities and type of metabolites excreted that could not be explained by blood phenylalanine levels. In a PKU pregnancy large quantities of phenylalanine metabolites were found in urine despite a modest elevation of serum phenylalanine. Increase in the excretion of phenylalanine metabolites was found in patients who were considered to have good blood phenylalanine control. These preliminary studies indicate that the current practice of allowing a wide range of blood phenylalanine in the treatment of PKU may have to be reexamined. Since these metabolites are neurotoxic, they may afford a new parameter for the study of PKU not only regarding the prevention of mental retardation but also with regards to behavior and learning disabilities.