Inborn errors of amino acid metabolism phenylketonuria pku 3

An infant was recently diagnosed with phenylketonuria (PKU) following a newborn screening. Which of the following enzymes is most likely deficient in this patient?

1: Tyrosinase
2: Dihydropteridine reductase (DHPR)
3: Tryptophan hydroxylase
4: Phenylalanine hydroxylase