Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Refsum disease ?
    ### Response:
    Refsum disease is an inherited condition that causes vision loss, absence of the sense of smell (anosmia), and a variety of other signs and symptoms.  The vision loss associated with Refsum disease is caused by an eye disorder called retinitis pigmentosa. This disorder affects the retina, the light-sensitive layer at the back of the eye.
    