Serum Phenylalanine and Tyrosine Levels in the Newborn Infant

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Abstract
PHENYLKETONURIA is a hereditary metabolic disease caused by a deficiency of the enzyme, phenylalanine hydroxylase. Data have been presented showing that the mental retardation in this condition can be effectively prevented if treatment with a diet low in phenylalanine content is started very early in infancy.1 During the past few years a number of reports2 3 4 5 have appeared on the testing of urine for phenylpyruvic acid as a means of screening for phenylketonuria among newborn infants. Although this test is relatively simple from the technical point of view the affected infant frequently does not show a positive test until four to . . .