Possible causes of increases in extracellular/plasma glutamate levels are also speculative at present, but may include increased release, e.g., via the above-mentioned upregulation of the Xc− system itself, or a downregulation of the glutamate importer GLAST (EAAT1), which can occur upon hyperglycemia as relevant to the present OSA group [61]. The gene discussed is SLC1A3; the disease is obstructive sleep apnea syndrome.