Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to sickle cell disease ?
    ### Response:
    Mutations in the HBB gene cause sickle cell disease.  Hemoglobin consists of four protein subunits, typically, two subunits called alpha-globin and two subunits called beta-globin. The HBB gene provides instructions for making beta-globin. Various versions of beta-globin result from different mutations in the HBB gene.
    