Adequate phenylalanine intake for optimum growth and development in the treatment of phenylketonuria

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Abstract
Early diagnosed PKU patients were divided into two groups according to whether their plasma phenylalanine levels had been maintained at less than 2 or between 3 and 10 mg/100 ml during the period of rapid brain development in early infancy. The physical growth and mental development of both groups were compared with standard values from normal children and with growth and development of their own unaffected siblings. Infants whose plasma phenylalanine levels were below 2 mg/100 ml often did not maintain their original growth percentile standings and at 12 months of age ranked lower in percentile weight and height than their unaffected siblings. Patients whose plasma phenylalanine levels were between 3 and 10 mg/100 ml maintained growth percentile ratings similar to those of their unaffected siblings. Patients in the more restricted group scored significantly (P < 0.05) below their unaffected siblings on learning tests, whereas there was no difference (P > 0.05) between scores of patients in the less restricted group and those of their unaffected siblings. A highly significant difference (P < 0.005) was found between the developmental scores of the two patient groups. The results of this study demonstrate that the dietary phenylalanine required by PKU infants is the same as that minimum required by normal infants of the same age. It is recommended that the neonate with PKU receive an initial phenylalanine intake of 60 mg/kg body wt. From this, fine adjustments are made according to individual requirements for normal growth and in order to maintain plasma phenylalanine levels between 3 and 10 mg/100 ml, which the authors consider to be the safest range for optimum growth and development.