Hyperphenylalaninemia with defective transamination

Blood phenylalanine concentrations in a female neonate increased slowly to a level at which dietary phenylalanine restriction became necessary. At this point the patient's urinary aromatic acid excretion profile showed only minimal amounts of phenylpyruvic acid or related aromatic acids. Phenylalanine-tolerance tests, and a subsequent challenge with a normal diet for three days, revealed a progressive decline in the blood phenylalanine concentration at which transamination started to occur. This fits the classification of 'hyperphenylalaninemia with transamination defect'. Possible explanations for the defective metabolism are discussed in the light of the experimental findings.