Currently, three loci associated with X-linked congenital nystagmus have been mapped on the X-chromosome, where NYSTAGMUS 1 (NYS1) is located at Xq26–q27 (OMIM #310700), NYS5 at Xp11.4–p11.3 (OMIM %300589), and NYS6 at Xp22.3–p22.2 (OMIM #300814).The G-protein coupled receptor 143 (GPR143) and the FERM domain–containing 7 (FRMD7) genes are two disease-causing genes identified from the regions of Xp22.3–p22.2 and Xq26-q27 respectively. The gene discussed is GPR143; the disease is congenital nystagmus.