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. Symptoms may include muscle stiffness in the trunk and limbs, and heightened sensitivity to noise, touch, and emotional distress, which can set off muscle spasms.
    