Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to phenylketonuria ?
    ### Response:
    Mutations in the PAH gene cause phenylketonuria.  The PAH gene provides instructions for making an enzyme called phenylalanine hydroxylase. This enzyme converts the amino acid phenylalanine to other important compounds in the body. If gene mutations reduce the activity of phenylalanine hydroxylase, phenylalanine from the diet is not processed effectively.
    