Hyperphenylalaninemia due to a deficiency of biopterin--a variant form of phenylketonuria
1978
Kaufman, Seymour | Berlow, Stanley | Summer, George K. | Milstien, Sheldon | Schulman, Joseph D. | Orloff, Sheldon | Spielberg, Stephen | Pueschel, Siegfried
Extract: The components of the hepatic phenylalanine hydroxylating system in a child with phenylketonuria who showed substantial neurologic impairment despite early dietary control of elevated blood phenylalanine levels were studied. Phenylalanine hydroxylase, dihydropteridine reductase and dihydrofolate reductase activities were normal. In contrast the level of hydroxylation cofactor, tetrahydrobiopterin, in liver was only 10 percent of normal. Serum and urinary levels of biopterin-like compounds were also low, and the serum biopterin did not increase in response to a phenylalanine load as its does in normal and phenylketonuric subjects. The phenylalanine hydroxylase activity was 2.3 percent of the normal value. These results indicate that the child suffers from a deficiency of a functional phenylalanine hydroxylating system secondary to a defect in biosynthesis of biopterin.
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