For example, loss of DmNmnat in photoreceptors causes retinal degeneration2; loss-of-function mutations in human Nmnat1 cause Leber congenital amaurosis 9 (LCA9)3, 4, 5, 6, a childhood blindness disease that involves degeneration of the photoreceptors3, 5, 7; and loss of mouse Nmnat2 causes axonal degeneration8. This evidence concerns the gene NMNAT1 and Leber congenital amaurosis 9.