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LETTER TO THE EDITOR

Sir, In their article, “Urinary Phenylalanine Excretion in Hyperphenylalaninaemic Children” (Acta Paediat Scand, 62: 333, 1973), F. Guttler & F. Rosleff present data which they state do not support our suggestion that hyperphenylalaninemic patients are protected by their increased urinary excretion of phenylalanine. They rightly point out that our suggestion was merely a hypothesis: indeed we hoped it would promote further research such as that performed by Guttler and Rosleff. However, I would contend that the hypothesis is not completely excluded by their study in which they gave a highly unphysiologic dose of phenylalanine. In addition, their phenylketonuric children were on low phenylalanine milk substitutes which both we and others (Clayton, B. E., Francis, D. E. M., Shepherd, J. & Wolff, 0. K.: Arch Dis Child, 45:640, 1970, and Clayton, B. E., Heeley, A. F. & Heely, M.: Brit J Nutr, 24:573, 1970) have shown to cause an amino aciduria; whereas the comparison we made was between phenylketonuric children on normal diet and hyperphenylalaninaemic children on normal diet. In the light of this it is of great interest to note that the hyperphenylaninaemic children of Guttler and Rosleff, before loading, show a higher phenyia1anine:creatinine ratio than the phenylketonuric children when the serum concentrations of phenylalanine in both groups were identical. Thus, while the article of Guttler & Rosleff does not confirm our hypothesis, it has not disproved it.