ABSTRACT
Stiff person syndrome (SPS) is a rare central nervous system disorder characterized by fluctuating muscle rigidity of truncal and proximal limb muscles with superimposed spasms1-4. Continuous contraction of agonist and antagonist muscles caused by involuntary motor unit firing at rest are the hallmark clinical and electrophysiological signs of the disease2. The cause of SPS is unknown, but an autoimmune pathogenesis is suspected based on:
(1) The presence of antibodies against glutamic acid decarboxylase (GAD65), the ratelimiting enzyme for the synthesis of γ-aminobutyric acid (GABA)2,5-7;
(2) The observation that these antibodies are produced intrathecally and may be pathogenic because they inhibit the activity of the inhibitory neurotransmitter GABA, resulting in low GABA levels in the brain and cerebrospinal fluid (CSF)8-10;
(3) Association with other autoimmune disorders, autoantibodies and alleles in the DR and DQ phenotypes 1, 2.
