RPGR and retinitis pigmentosa: The study also rules out the possibility that other tubulin family members like TTLL6 or TTLL7 could glutamylate RPGR, compensating for the loss of TTLL5. Mutations in these two genes could also affect humans, causing blindness and photoreceptor degeneration, like retinitis pigmentosa or cone/cone-rod dystrophies (Sun et al., 2016).