Intrinsic differences between the neural stem/progenitor cells used in these studies and adherently cultivated NS cells which represent a pure population of symmetrically dividing tripotent neural stem cells [38–40], or the time point of NS cell transplantation prior to the onset of retinal degeneration in the nclf mutant [17] may account for these apparently discrepant observations. This evidence concerns the gene CLN6 and retinal degeneration.