Stiff-person syndrome associated with cerebellar ataxia and high glutamic acid decarboxylase antibody titer.

Glutamic acid decarboxylase (GAD) is the main target of humoral autoimmunity in patients with insulin-dependent diabetes mellitus (IDDM) and stiff-person syndrome. We reviewed the case of a 46-year-old woman who had cerebellar ataxia before getting stiff-person syndrome and IDDM with high anti-GAD autoantibody titers. This was a rare case in which there were both the clinical symptoms of stiff-person syndrome and cerebellar ataxia. In western blot analysis her serum reacted with 65-kDa proteins from rat cerebellum, cerebral cortex, and spinal cord. Autoantibodies to GAD may cause functional impairment of gamma-aminobutyric acid (GABA) neurons in the spinal cord as well as in the cerebellum.