By genomic sequencing of affected and unaffected animals from all 6 lines, we found that the naturally occurring RD8 mutation, a single base pair deletion in exon 9 of the Crb1 gene, co-segregates 100% with the observed early-onset inferior retinal degeneration in the original CCDKO mouse line as well as in all three re-derived “affected” Ccl2−/−, Cx3cr1−/− and Ccl2−/−/Cx3cr1−/− “single” and “double” chemokine knockout mouse lines. Here, CCL2 is linked to retinal degeneration.