TOPORS and retinitis pigmentosa: While RNF4 loss is embryonic lethal in mice (Hu et al, 2010), mutations in TOPORS are associated with a variant of retinitis pigmentosa (Chakarova et al, 2007) characterised by apoptotic rod cells, and with Joubert syndrome (Strong et al, 2023), a rare disease characterised by brain stem anomalies and in some cases retinal dystrophy.