Dihydrobiopterin is used in management of which amino acid defect?

Ans. (c) PhenylalanineRef: Lippincott's Biochemistry, pg. 268Phenylketonuria (PKU), caused by a deficiency of phenylalanine hydroxylase and is the most common clinically encountered inborn error of amino acid metabolism (prevalence 1:11,000). Hyperphenylalaninemia may also be caused by deficiencies in the enzymes that synthesize or reduce the coenzyme tetrahydrobiopterin (BH4 ). It is important to distinguish among the various forms of hyperphenylalaninemia, because their clinical management is different. For example, a small fraction of PKU is a result of a deficiency in either dihydropteridine (BH2 ) reductase or BH2 synthetase. These mutations prevent synthesis of BH4 , and indirectly raise phenylalanine concentrations, because phenylalanine hydroxylase requires BH4 as a coenzyme. BH4 is also required for tyrosine hydroxylase and tryptophan hydroxylase, which catalyze reactions leading to the synthesis of neurotransmitters, such as serotonin and catecholamines.