The WIDESPREAD use of mass screening for blood phenylalanine among newborns has led to the recognition that in addition to phenylketonuria (PKU),1 there may exist several closely related clinical and biochemical abnormalities, which have been variously labeled "hyperphenylalaninemia associated with phenylalanine transaminase deficiency,"2 "persistent hyperphenylalaninemia,"3-5 "phenylalaninemia,"6 and "transient hyperphenylalaninemia."7,8 This report describes the results of phenylalanine to tolerance tests performed during a collaborative study on the causes for high phenylalanine levels, associated with normal serum tyrosine, in newborn infant screening programs.
Materials and Methods
Definition of Cases.—The present survey covers the family members of all infants with persistent blood phenylalanine levels of 6 mg/100 ml or higher and with blood tyrosine levels less than 5 mg/100 ml, seen during 1964 to 1966, and in a few instances, during the first quarter of 1967, from 11 centers located in seven states (California, Colorado, Illinois, New
Cunningham GC, Day RW, Berman JL, Hsia DY. Phenylalanine Tolerance Tests: In Families With Phenylketonuria and Hyperphenylalaninemia. Am J Dis Child. 1969;117(6):626–635. doi:10.1001/archpedi.1969.02100030628003
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