What is Stiff-Person Syndrome, the disease Celine Dion has been diagnosed with?

Singer Celine Dion has revealed that she has been diagnosed with Stiff-Person Syndrome (SPS), which is a rare and progressive neurological disorder. Symptoms of SPS may include stiff muscles in the trunk (torso), arms, and legs; greater sensitivity to noise, touch, and emotional distress, which can set off muscle spasms. Many people suffering from SPS fall frequently.