Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Dihydropteridine reductase deficiency ?
    ### Response:
    Dihydropteridine reductase deficiency (DHPR) is a severe form of hyperphenylalaninemia (high levels of the amino acid phenylalanine in the blood) due to impaired renewal of a substance known as tetrahydrobiopterin (BH4). Tetrahydrobiopterin normally helps process several amino acids, including phenylalanine, and it is also involved in the production of neurotransmitters.
    