Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to glycogen storage disease type IX ?
    ### Response:
    Mutations in the PHKA1, PHKA2, PHKB, or PHKG2 genes are known to cause GSD IX. These genes provide instructions for making pieces (subunits) of an enzyme called phosphorylase b kinase. The enzyme is made up of 16 subunits, four each of the alpha, beta, gamma, and delta subunits.
    