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Tetrahydrobiopterin loading test in hyperphenylalaninemia.
Pediatr Res. 1991 Nov; 30(5):435-8.PR

Abstract

Some cases of primary hyperphenylalaninemia are not caused by the lack of phenylalanine hydroxylase, but by the lack of its cofactor tetrahydrobiopterin. These patients are not clinically responsive to a phenylalanine-restricted diet, but need specific substitution therapy. Thus, it became necessary to examine all newborns screened as positive with the Guthrie test for tetrahydrobiopterin deficiency. Methods based on urinary pterin or on specific enzyme activity measurements are limited in their availability, and the simplest method, based on the lowering of serum phenylalanine after loading with cofactor, was discouraged by the finding that some dihydropteridine reductase-deficient patients were unresponsive. The preliminary observation that this limitation could be overcome by increasing the dose of the administered cofactor prompted us to reevaluate the potential of the tetrahydrobiopterin loading test in hyperphenylalaninemia. Fifteen patients, eight with ultimate diagnosis of phenylketonuria, three with 6-pyruvoyl tetrahydropterin synthase-, and four with dihydropteridine reductase-deficiency, have been examined by administering synthetic tetrahydrobiopterin both orally, at doses of 7.5 and 20 mg/kg, and i.v., at a dose of 2 mg/kg. All the tetrahydrobiopterin-deficient patients, unlike those with phenylketonuria, responded to the oral dose of 20 mg/kg cofactor by lowering their serum phenylalanine concentration markedly below baseline to an extent easily detectable by Guthrie cards. This method allows for a simple screening method when enzyme or pterin studies are not available.

Authors+Show Affiliations

Institute of Pediatric Clinic, University of Torino, Italy.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

1754298

Citation

Ponzone, A, et al. "Tetrahydrobiopterin Loading Test in Hyperphenylalaninemia." Pediatric Research, vol. 30, no. 5, 1991, pp. 435-8.
Ponzone A, Guardamagna O, Ferraris S, et al. Tetrahydrobiopterin loading test in hyperphenylalaninemia. Pediatr Res. 1991;30(5):435-8.
Ponzone, A., Guardamagna, O., Ferraris, S., Ferrero, G. B., Dianzani, I., & Cotton, R. G. (1991). Tetrahydrobiopterin loading test in hyperphenylalaninemia. Pediatric Research, 30(5), 435-8.
Ponzone A, et al. Tetrahydrobiopterin Loading Test in Hyperphenylalaninemia. Pediatr Res. 1991;30(5):435-8. PubMed PMID: 1754298.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Tetrahydrobiopterin loading test in hyperphenylalaninemia. AU - Ponzone,A, AU - Guardamagna,O, AU - Ferraris,S, AU - Ferrero,G B, AU - Dianzani,I, AU - Cotton,R G, PY - 1991/11/1/pubmed PY - 1991/11/1/medline PY - 1991/11/1/entrez SP - 435 EP - 8 JF - Pediatric research JO - Pediatr Res VL - 30 IS - 5 N2 - Some cases of primary hyperphenylalaninemia are not caused by the lack of phenylalanine hydroxylase, but by the lack of its cofactor tetrahydrobiopterin. These patients are not clinically responsive to a phenylalanine-restricted diet, but need specific substitution therapy. Thus, it became necessary to examine all newborns screened as positive with the Guthrie test for tetrahydrobiopterin deficiency. Methods based on urinary pterin or on specific enzyme activity measurements are limited in their availability, and the simplest method, based on the lowering of serum phenylalanine after loading with cofactor, was discouraged by the finding that some dihydropteridine reductase-deficient patients were unresponsive. The preliminary observation that this limitation could be overcome by increasing the dose of the administered cofactor prompted us to reevaluate the potential of the tetrahydrobiopterin loading test in hyperphenylalaninemia. Fifteen patients, eight with ultimate diagnosis of phenylketonuria, three with 6-pyruvoyl tetrahydropterin synthase-, and four with dihydropteridine reductase-deficiency, have been examined by administering synthetic tetrahydrobiopterin both orally, at doses of 7.5 and 20 mg/kg, and i.v., at a dose of 2 mg/kg. All the tetrahydrobiopterin-deficient patients, unlike those with phenylketonuria, responded to the oral dose of 20 mg/kg cofactor by lowering their serum phenylalanine concentration markedly below baseline to an extent easily detectable by Guthrie cards. This method allows for a simple screening method when enzyme or pterin studies are not available. SN - 0031-3998 UR - https://wwww.unboundmedicine.com/medline/citation/1754298/Tetrahydrobiopterin_loading_test_in_hyperphenylalaninemia_ L2 - https://doi.org/10.1203/00006450-199111000-00008 DB - PRIME DP - Unbound Medicine ER -