Large neutral amino acid therapy and phenylketonuria: a promising approach to treatment.

[classical phenylketonuria]

Six subjects with classical phenylketonuria (PKU ) were treated with large neutral amino acid supplements (PreKUnil , Nilab , Dk ) at 0 .4 g /kg /day in equally divided doses three times each day on an increased natural protein diet . All six subjects had low or deficient blood concentrations of both tyrosine and tryptophan , which are precursors for dopamine and serotonin , respectively , at the beginning of the study and were increased substantially throughout the study . Blood phenylalanine concentrations remained essentially unchanged , while the brain phenylalanine concentrations gradually decreased toward the carrier range as seen in parents of children with PKU . Two subjects were diagnosed with clinical depression and were in counseling programs at initiation of the study . At the end of the study all patients reported increased energy and overall improvement in well-being .