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In 6 patients with classic phenylketonuria (PKU) the plasma and cerebrospinal fluid (CSF) concentrations of phenylalanine and tyrosine were measured fluorimetrically. The results of the PKU group were compared with data obtained from 17 children without abnormal CSF parameters and free of metabolic or central nervous disorders, in whom a diagnostic lumbal puncture has been performed. The PKU patients showed statistically significant differences in comparison with the controls: plasma and CSF phenylalanine contents were markedly higher (on the average 6.4 and 4.6 times, respectively) in PKU patients. Plasma tyrosine was 1.8 times lower, but CSF tyrosine was about 2.2 times higher in comparison to the controls. In general, the plasma CSF-ratio ( PLR ) of phenylalanine did not change in PKU and could be found in the same range as in the normal controls. In contrast to this, the PLR of tyrosine was found to be significantly lower in PKU patients. The results are discussed with respect to an altered function of the brain barrier systems for the amino acid transport in PKU, and that increased CSF tyrosine contents in PKU may rather reflect disturbances of the intracellular metabolism of the brain cells than changes of the amino acid transport through the brain barrier produced by hyperphenylalaninemia.

Plasma and cerebrospinal fluid concentrations of tyrosine and phenylalanine were measured fluorometrically in human term neonates appropriate for gestational age and in neonates small for gestational age with severe intra-uterine growth retardation of Type II. The intra-uterine retarded newborns showed significant differences of both plasma and cerebrospinal fluid tyrosine levels as compared with the non-retarded newborns: the mean plasma and cerebrospinal fluid tyrosine were determined to be 2.0 and 2.5 times, respectively, higher in the retarded group. The mean cerebrospinal fluid phenylalanine content was also increased in these newborns. The findings may reflect cellular disturbances of the tyrosine metabolization in the developing brain as it can also be found in experimental intra-uterine growth retarded animals.