Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Rett Syndrome ?
    ### Response:
    Rett syndrome is a rare genetic disease that causes developmental and nervous system problems, mostly in girls. It's related to autism spectrum disorder. Babies with Rett syndrome seem to grow and develop normally at first. Between 3 months and 3 years of age, though, they stop developing and even lose some skills.
    