RPGR and retinitis pigmentosa: Retinitis Pigmentosa (RP) is an irreversible hereditary retinopathy caused by deleterious mutations in TRNT1 (TRNA Nucleotidyl Transferase 1), RPGR (Retinitis Pigmentosa GTPase Regulator), USH2A (Usher Syndrome Type IIA; Usherin), PDE6B (Phosphodiesterase 6B), RP2 (retinitis pigmentosa 2 homolog), and other genes.