Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Glycogen storage disease type 13 ?
    ### Response:
    What causes glycogen storage disease type 13? Glycogen storage disease type 13 (GSD13) is caused by changes (mutations) in the ENO3 gene.  Glycogen is a substance that is stored in muscle tissue and is used as an important source of energy for the muscles during movement and exercise.
    