In surviving animals, photoreceptors failed to generate outer segments, but axonemes and rudimentary connecting cilia were present before photoreceptor degeneration.15,18 Although photoreceptor death and perinatal lethality in Ahi1-null mice was consistent with deficits in cilia function, the severity of these phenotypes limits their use for studying genetic interactions that modulate the degree of retinal degeneration. The gene discussed is AHI1; the disease is retinal degeneration.