PEDIATRICS Vol. 33 No. 4 April 1964, pp. 512-525
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PHENYLALANINE HYDROXYLASE ACTIVITY IN NEWBORN INFANTS

I. Relation to the Appearance of Metabolites in Blood and Urine in Normal and Enzyme Deficient States

Richard J. Allen M.D., B.S.1, John C. Heffelfinger M.D.1, Ronald E. Masotti M.D.1, and Makepeace U Tsau Ph.D.1

1 The Pediatric-Neurology Unit, Department of Pediatrics, University of Michigan Medical Center, Ann Arbor, Michigan

One of the techniques that may be employed to expedite the diagnosis of phenylketonuria in the newborn infant is the phenylalanine load test. However, this is probably an impractical method for a routine examination but in the suspected sibling may permit rapid differentiation of an affected infant from one entirely normal. Also, carriers may simulate phenylketonuric infants so that the diagnosis must still rest on the appearance of abnormal metabolites in the urine.

Of 15 suspected infants, three proved to have typical phenylketonuria very early while four others demonstrated elevated phenylalanine levels in load tests in the newborn period and on serial follow-up, which might otherwise suggest the disease. Studies of these infants showed that they did not have phenylketonuria and that they were in all probability carriers. The carrier state which has been extensively studied in adults may therefore occur in the neonate and may be confused in the clinical diagnosis with the phenylketonuric infant. The proven phenylketonuric infants developed abnormal metabolites in the urine within the first few days of life so that the diagnosis could be corroborated by the simple ferric chloride test in addition to chromatographic methods which detected o-HPA and phenylalanine.

Also ten infants with phenylketonuria diagnosed at less than two months of age are included in this report. They consist of four infants who were "first cases" in the family and six infants diagnosed as the result of a known older sibling. Three infants were recognized by our study of 15 suspected newborns horn into 13 different families where phenylketonuria was known to be present. Positive urine ferric chloride tests appeared as early as two days of age and indicated that ferric chloride testing is useful in the newborn. If, however, the diagnosis is established by elevated serum phenylalanine levels the child should probably not be treated for phenylketonuria until other typical metabolites are identified.

Submitted on August 12, 1963
Accepted on October 18, 1963




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J. P. Brosco, L. M. Sanders, M. I. Seider, and A. C. Dunn
Adverse Medical Outcomes of Early Newborn Screening Programs for Phenylketonuria
Pediatrics, July 1, 2008; 122(1): 192 - 197.
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