M. Blaskovics, T. Giudici, N. Blau
1991
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Abstract
Primapterinuria is the recently discovered variant of hyperphenylalaninemia characterized by the excretion of 7-substituted pterins in the patients urine (1). Primapterinuria differs from the classical PKU and other variants of tetrahydrobiopterin deficiency because these patients do not need treatment with a lowphenylalanine diet or with neurotransmitter precursors L-DOPA and 5-hydroxytryptophan. The first patients were described by Dhondt et al. (2) and Blaskovics & Giudici (3). A loading test with tetrahydrobiopterin was the first indication that primapterin (7-biopterin) may derive from 6-biopterin (4). Tetrahydrobiopterin, dihydrobiopterin and sepiapterin given orally resulted in a significant increase in 6and 7-substituted biopterin, and the ratio remained the same (1.0 to 1.5) after loading (5). From in vitro experiments it is known that primapterin can be formed during the phenylalanine-4-hydroxylase reaction in a pterin-4a-carbinolamine dehydratase free system (6). To the present time all known enzymes involved in the biosynthesis or regeneration of tetrahydrobiopterin have been found to be normal in these patients and a pterin-4a-carbinolamine dehydratase deficiency has been proposed (Fig. 1).