Another tubulin-modifying enzyme, TTLL5, a tubulin polyglutamylase, is also associated with cone-rod dystrophy type 9 (CORD9) and RP (Sergouniotis et al., 2014; Astuti et al., 2016; Bedoni et al., 2016) although it is thought that this is due to defective glutamylation of RPGR (Sun et al., 2016). This evidence concerns the gene RPGR and retinitis pigmentosa 1.