Because of the high variability in mutant phenotypes, we occasionally observed severe retinal degeneration as early as 6 months (Fig. 4G), and those retinas had photoreceptor rosette formation, Müller glial activation (GFAP upregulation), and loss of RGCs, as seen in older mutant retinas (Fig. 3). This evidence concerns the gene GFAP and retinal degeneration.