We have previously shown that Tyro3 mouse mutants, Gas6 mouse mutants, and retina-specific Pros1 mouse mutants all have a normal number of PRs at this time (Prasad et al., 2006; Burstyn-Cohen et al., 2012); but that Gas6/Pros1 double mutants display PR death and retinal degeneration that fully phenocopies the degeneration of the Mertk mutants (Burstyn-Cohen et al., 2012). The gene discussed is MERTK; the disease is retinal degeneration.