In a recent study of CCDKO (Ccl2−/−/Cx3cr1−/−) mice that were backcrossed to generate re-derived, closely related Ccl2−/−, Cx3cr1−/− and Ccl2−/−/Cx3cr1−/− mouse lines, we identified the rd8 mutation in the Crb1 gene as a dominant confounding factor that was responsible for the early onset retinal degeneration previously attributed to the combined deficiency of Ccl2 and Cx3cr1 in CCDKO mice (Luhmann et al., 2012; Tuo et al., 2007). This evidence concerns the gene CRB1 and retinal degeneration.