RPGR and Abnormal retinal morphology: RPGR is another major cause of XLRP (Meindl et al., 1996, reviewed byAdams et al., 2007) and RPGRis anchored to the connecting cilium by another retinal disease gene productthe RPGR-interacting protein (RPGRIP), a structural component of the ciliaryaxoneme (Hong et al., 2001).Interestingly, Arl3 interacts with the phosphodiesterase delta (PDEδ),which is also an interacting partner of RPGR (Linari et al., 1999a, b).