Initial data in Drosophila mutants showed that expression of ceramidase suppresses retinal degeneration in arrestin mutant flies, in parallel to a decrease in Cer levels; however, these mutants show enhanced degeneration of photoreceptors when they are raised with a Sph-enriched diet, suggesting that Sph is not involved in preventing degeneration (Acharya et al., 2003). This evidence concerns the gene CBLN1 and retinal degeneration.