Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Usher syndrome ?
    ### Response:
    Usher syndrome is a condition characterized by hearing loss or deafness and progressive vision loss. The loss of vision is caused by an eye disease called retinitis pigmentosa (RP), which affects the layer of light-sensitive tissue at the back of the eye (the retina).
    