Mas-related G protein-coupled receptor member X1 (MRGX) is a sensory neuron-specific G protein-coupled receptor that is involved in the function of nociceptive neurons. This integral membrane protein may also regulate nociceptor development and/or the sensation or modulation of pain. There are four members (MRGX1-4) in the human MRGX familly. MRGX1 and MRGX2 receptors stimulate both G Alpha q- and G Alpha i -regulated pathways, while MRGX3 and MRGX4 receptors mainly activate G Alpha q-regulated pathways. G Alpha q proteins are involved in the calcium-signaling pathway downstream of the MRGX receptors. MRGX receptors are unique in that they are expressed in a subset of small dorsal root and trigeminal sensory neurons.