Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to xeroderma pigmentosum ?
    ### Response:
    Xeroderma pigmentosum is caused by mutations in genes that are involved in repairing damaged DNA. DNA can be damaged by UV rays from the sun and by toxic chemicals such as those found in cigarette smoke. Normal cells are usually able to fix DNA damage before it causes problems.
    