NUTRITIONAL-VALUE OF ESSENTIAL AMINO-ACIDS IN THE TREATMENT OF ADULTSWITH PHENYLKETONURIA

Phenylketonuria (PKU; McKusick 261600) is an inherited metabolic disor der caused by a deficiency of phenylalanine hydroxylase. Hyperphenylal aninaemia results in progressive mental deterioration, unless treatmen t with dietary phenylalanine (phe) restriction starts before 6 weeks o f age (Scriver et al 1989). Since termination of the treatment leads t o a deterioration of the intellectual and neurophysiological functions , a 'diet for life' is recommended (Michals et al 1990). The recogniti on that phe and other large neutral amino acids (LNAA) share common re ceptor sites on a blood-brain barrier transport system (Oldendorf 1973 ) led to the hypothesis that the administration of those LNAA to PKU p atients may reduce the amount of phe reaching the brain and prevent so me of its toxic effects on the central nervous system. Short- and long -term trials conducted in animals and humans showed that motor and cog nitive functions improved with the addition of branched-chain amino ac ids to the low-phe diet (Berry et al 1990). However, little is known a bout the bioavailability and the nutritional value of this essential a mino 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.