NUTRITIONAL-VALUE OF ESSENTIAL AMINO-ACIDS IN THE TREATMENT OF ADULTS WITH PHENYLKETONURIA

Phenylketonuria (PKU; McKusick 261600) is an inherited metabolic disorder caused by a deficiency of phenylalanine hydroxylase. Hyperphenylalaninaemia results in progressive mental deterioration, unless treatment with dietary phenylalanine (phe) restriction starts before 6 weeks of age (Scriver et al 1989). Since termination of the treatment leads to a deterioration of the intellectual and neurophysiological functions, a 'diet for life' is recommended (Michals et al 1990). The recognition that phe and other large neutral amino acids (LNAA) share common receptor sites on a blood-brain barrier transport system (Oldendorf 1973) led to the hypothesis that the administration of those LNAA to PKU patients may reduce the amount of phe reaching the brain and prevent some of its toxic effects on the central nervous system. Short- and long-term trials conducted in animals and humans showed that motor and cognitive functions improved with the addition of branched-chain amino acids to the low-phe diet (Berry et al 1990). However, little is known about the bioavailability and the nutritional value of this essential amino acids mixture. To determine whether adult PKU patients who refuse to continue taking their classical amino acids mixture may replace it by LNAA, a nitrogen (N) balance was conducted in four PKU patients.