Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Glycogen storage disease type 4 ?
    ### Response:
    What causes glycogen storage disease type 4? Glycogen storage disease type 4 (GSD 4) is caused by mutations in the GBE1 gene. The GBE1 gene normally provides instructions for making the glycogen branching enzyme. This enzyme is necessary for making glycogen, a major source of stored energy in the body.
    