These include variants in the NAD+ or NADPH dependent retinal dehydrogenases like RDH12 that cause LCA13 (Schuster et al., 2007) and the GTP synthesis enzyme IMPDH1 that causes retinitis pigmentosa (Kennan et al., 2002; Bowne et al., 2002). This evidence concerns the gene RDH12 and retinitis pigmentosa.