The phenotype of Rab8-GEF-deficient Rabin8-F201A mutant that caused the substantial enlargement of RTCs in Xenopus rods resembles that of Rab8-T22N GTP-binding-deficient mutant rods, which featured massive accumulation of irregular fusion-incompetent RTCs at the ciliary base triggering rod cell death and retinal degeneration (Moritz et al., 2001). The gene discussed is RAB8A; the disease is retinal degeneration.