GNAQ (guanine nucleotide-binding protein G(q) subunit alpha) is a GTPase activated upon ligand binding of a G-protein coupled receptor. Hotspot mutations impair GTPase activity, resulting in constitutive pathway activation and are common in uveal melanoma. Simple variants in GNAQ are seen in about 1.5% of all tumors, including 4% of skin tumors and 27% of eye tumors, where it is diagnostic for uveal melanoma.