Other examples of the SUMO regulatory roles in vision are illustrated by the fact that mutations in the dual Ubiquitin/SUMO E3 ligase TOPORS gene cause retinitis pigmentosa in human (Chakarova et al., 2007) (RetNet, http://www.sph.uth.tmc.edu/RetNet/); and the SUMO ligases HDAC4 and TLS have been also involved in photoreceptor survival or apoptosis (Chen and Cepko, 2009; Chen et al., 2011). The gene discussed is TOPORS; the disease is retinitis pigmentosa.