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

Six subjects with classical phenylketonuria (PKU) were treated with large neutral amino acid supplements (PreKUnil, Nilab, Dk) at 0.4g/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.