The GPCR superfamily is the largest gene family in the human genome containing approximately 800 genes. As the vertebrate superfamily can be phylogenetically grouped into five main families the GRAFS classification system has been proposed.
↑Fredriksson, R; Lagerström, MC; Lundin, LG; Schiöth, HB (June 2003). "The G-protein-coupled receptors in the human genome form five main families. Phylogenetic analysis, paralogon groups, and fingerprints". Molecular Pharmacology. 63 (6): 1256–72. doi:10.1124/mol.63.6.1256. PMID12761335.