G protein-coupled receptor for bile acids, which is specifically expressed in sensory neurons of dorsal root ganglion and is involved in itch perception (PubMed:31068464, PubMed:31500698, PubMed:34789874, PubMed:38718132, PubMed:39476841). Activated by bile acids, such as deoxycholate, chenodeoxycholate, taurocholate, taurodeoxycholate and taurodeoxycholate (PubMed:31068464, PubMed:31500698, PubMed:39476841). Has a preference for 3-sulfated bile acids, such as deoxycholate 3-sulfate, glycoursodeoxycholate 3-sulfate and tauroursodeoxycholate 3-sulfate, which are present at high level in cholestatic patients with itch symptoms (PubMed:39476841). Bile acid- binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of downstream effectors (PubMed:30768591, PubMed:31068464, PubMed:31500698, PubMed:34789874, PubMed:38718132, PubMed:39476841). MRGPRX4 is coupled to G(q)/G(11) G alpha proteins and activates phospholipase C-beta, releasing diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3) second messengers that modulate the activity of phosphatidylinositol 3-kinase and promote the release of Ca2+ ions from intracellular stores, respectively (PubMed:30768591, PubMed:31068464, PubMed:31500698, PubMed:34789874, PubMed:38718132, PubMed:39476841). {ECO:0000269|PubMed:30768591, ECO:0000269|PubMed:31068464, ECO:0000269|PubMed:31500698, ECO:0000269|PubMed:34789874, ECO:0000269|PubMed:38718132, ECO:0000269|PubMed:39476841}. This is the function of Ensembl gene identifier ENSG00000179817 (MRGPRX4, MAS related GPR family member X4).