Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Opitz G/BBB syndrome ?
    ### Response:
    What causes Opitz G/BBB syndrome? The X-linked form of Opitz G/BBB syndrome is caused by mutations in the MID1 gene. The MID1 gene provides instructions for making a specific protein called midline-1. This protein helps regulate the function of microtubules, which are rigid, hollow fibers that make up the cell's structural framework (the cytoskeleton).
    