Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to tetrahydrobiopterin deficiency ?
    ### Response:
    Tetrahydrobiopterin deficiency can be caused by mutations in one of several genes, including GCH1, PCBD1, PTS, and QDPR. These genes provide instructions for making enzymes that help produce and recycle tetrahydrobiopterin in the body. Tetrahydrobiopterin normally helps process several amino acids, including phenylalanine.
    