TLCD3B and retinal degeneration: However, despite rAAV8-CerS2 treatment having slightly better functional and morphological retention in the retina, the relative increase in the overall ceramide levels as well as that of TLCD3B profile ceramides were lower than those of rAAV8-CerS4-treated retinas (Fig. 6D), suggesting that the changes in the overall ceramide levels are not a major contributor to retinal degeneration in the context of TLCD3B loss of function.