P2RX7 and Huntington disease: The microglial and neuronal P2X7 receptor is an adenosine triphosphate–gated ion channel that has been found to be overexpressed in synaptic terminals in HD.110 Extracellular adenosine triphosphate, acting on this receptor, stimulates synaptic dysregulation and neuronal death through apoptotic and nonapoptotic mechanisms111; in HD model mice, a P2X7 antagonist reduced apoptotic neuronal death, weight loss, and motor deficits.110 P2X7 in both neurons and microglia is under investigation as a potential therapeutic target.