The exact cause of stiff person syndrome. Experts theorize the symptoms are triggered by an autoimmune reaction in which the immune system attacks a protein called glutamic acid decarboxylase (GAD), which helps make a substance called gamma-aminobutyric acid (GABA). GABA is a neurotransmitter that reduces or prevents certain nerve signals, and if GABA is unable to function properly, nerve cells can malfunction, too. As is the situation with someone who has SPS, the nervous system becomes overactive and overstimulated. This disruption of normal GABA function is thought to be what causes the symptoms of SPS, however it is not known what triggers this malfunction in the first place.
