Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Stiff-Person Syndrome ?
    ### Response:
    Stiff-person syndrome (SPS) is a rare neurological disorder with features of an autoimmune disease. SPS is characterized by fluctuating muscle rigidity in the trunk and limbs and a heightened sensitivity to stimuli such as noise, touch, and emotional distress, which can set off muscle spasms.
    