Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to glycogen storage disease type VII ?
    ### Response:
    Mutations in the PFKM gene cause GSDVII. This gene provides instructions for making one piece (the PFKM subunit) of an enzyme called phosphofructokinase, which plays a role in the breakdown of glycogen. The phosphofructokinase enzyme is made up of four subunits and is found in a variety of tissues.
    