Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Fibrous dysplasia ?
    ### Response:
    What causes fibrous dysplasia? The cause of fibrous dysplasia has been linked to a gene mutation that occurs after conception, in the early stages of fetal development. The mutation involves a gene that affects the cells that produce bone. People with fibrous dysplasia carry this mutation in some, but not all cells of their body.
    