Autoimmunity to GABAA-receptor-associated

Stiff-person syndrome (SPS) is an autoimmune neurological disorder characterized by autoantibodies to glutamic acid decarboxylase (GAD), the enzyme responsible for the synthesis of inhibitory neurotransmitter GABA. To search for biomarkers that distinguish SPS from other neurological disorders (OND), we used surface enhanced laser desorption/ionization-time of flight (SELDI-TOF) mass spectrometry to obtain pro-teomic profile of sera from 25 GAD-positive SPS patients and 25 controls. A significant decrease was found in the level of a protein corresponding to GABAA-receptor-associated protein (GABARAP), which is responsible for the stability and surface expression of the GABAA-receptor. Up to 70 % of the SPS sera examined, compared with 10 % of the controls, immunoprecipitated GABARAP protein. Antibodies raised against GABARAP immunostained neuronal cell bodies as well as axonal and dendritic processes, as visualized by confocal micro-scopy. In vitro experiments demonstrated that the IgG from GABARAP antibody-positive patients, but not control IgG, significantly inhibited the surface expression of GABAA-receptor.We conclude thatGABARAP is a new autoantigen in SPS. Because the patients ’ IgG inhibits the expression of GABAA-receptors, the circulating antibodies could impair GABAergic pathways and play a role in the clinical symptomatology of SPS patients