PEDIATRICS Vol. 79 No. 3 March 1987, pp. 374-378
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Guanosine Triphosphate Cyclohydrolase I Deficiency: Early Diagnosis by Routine Urine Pteridine Screening

Edwin W. Naylor PhD1, David Ennis BS1, A. George F. Davidson MD1, Lawrence T. K. Wong MD1, Derek A. Applegarth PhD1, and Alois Niederwieser PhD1

1 From the Department of Medical Genetics, The Western Pennsylvania Hospital, and the University of Pittsburgh, Pittsburgh; the Biochemical Diseases Clinical Service and the Biochemical Diseases Laboratory, British Columbia Children’s Hospital, Vancouver, British Columbia, Canada; and the Department of Pediatrics, University of Zurich, Zurich

A deficiency of hepatic guanosine triphosphate cyclohydrolase I is reported in a 4-month-old infant in whom positive results on a Guthrie phenylketonuria test in the neonatal period were found. Because of the significantly elevated serum phenylalanine levels a diagnosis of classical phenylketonuria was made, and dietary therapy was started. Urinary pteridine screening for cofactor variants, however, revealed extremely low levels of both neopterin and biopterin. This suggested the possibility of guanosine triphosphate cyclohydrolase I deficiency and led to additional confirmatory assays. Repeat urine, serum, and CSF pteridine profiles, combined with tetrahydrobiopterin-loading studies and the assay of guanosine triphosphate cyclohydrolase I activity in a liver biopsy, confirmed the defect. It is significant to note that the diagnosis was made before the onset of major clinical symptoms. This case illustrates the need for routine cofactor variant screening of all infants in whom hyperphenylalaninemia is diagnosed in the neonatal period.

Key Words: guanosine triphosphat • cyclohydrolase I deficiency • hyperphenylalaninemia • routine urine pteridine screening

Submitted on February 18, 1986
Accepted on April 28, 1986




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