Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Kidney Disease ?
    ### Response:
    Kidney disease -- also known as chronic kidney disease (CKD) -- occurs when kidneys can no longer remove wastes and extra water from the blood or perform other functions as they should. According to the Centers for Disease Control and Prevention, more than 20 million Americans may have kidney disease.
    