Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Gardner syndrome ?
    ### Response:
    What causes Gardner syndrome? Gardner syndrome is caused by changes (mutations) in the APC gene, which is called a "tumor suppressor." Tumor suppressor genes encode proteins that are part of the system that controls cell growth and division. These proteins ensure that cells do not grow and divide too quickly or in an abnormal manner.
    