Stiff-Person Syndrome: A condition characterized by persistent spasms (SPASM) involving multiple muscles, primarily in the lower limbs and trunk. The illness tends to occur in the fourth to sixth decade of life, presenting with intermittent spasms that become continuous. Minor sensory stimuli, such as noise and light touch, precipitate severe spasms. Spasms do not occur during sleep and only rarely involve cranial muscles. Respiration may become impaired in advanced cases. (Adams et al., Principles of Neurology, 6th ed, p1492; Neurology 1998 Jul;51(1):85-93)Glutamate Decarboxylase: A pyridoxal-phosphate protein that catalyzes the alpha-decarboxylation of L-glutamic acid to form gamma-aminobutyric acid and carbon dioxide. The enzyme is found in bacteria and in invertebrate and vertebrate nervous systems. It is the rate-limiting enzyme in determining GAMMA-AMINOBUTYRIC ACID levels in normal nervous tissues. The brain enzyme also acts on L-cysteate, L-cysteine sulfinate, and L-aspartate. EC 184.108.40.206.Syndrome: A characteristic symptom complex.