Inhibitory neurotransmission in the mammalian CNS is mainly mediated by the amino acids GABA and glycine. GABA receptors constitute major targets of widely used drugs such as barbiturates and benzodiazepines, whereas clinically applicable compounds that target GlyRs have yet to be identified. Glycine levels are highest in the brainstem and spinal cord where GlyRs are involved with the control of motor rhythm generation, the coordination of spinal responses and the processing of sensory signals. A disruption GlyR surface expression, or by reducing the ability of expressed GlyRs to conduct chloride ions, results in the rare neurological disorder, hyperekplexia. The disorder is characterized by an exaggerated response to unexpected stimuli which is followed by a temporary but complete muscular rigidity often resulting in an unprotected fall. Chronic injuries as a result of the falls are symptomatic of the disorder. A mutation in GLRA1 is responsible for some cases of stiff person syndrome.