GNAT1 and inherited retinal dystrophy: However, two recent clinical reports have implicated the novel type of homozygous GNAT1 mutations into a progressive retinal dystrophy.27,28 In Gnat1−/− mice, a few rows of photoreceptor nuclei are lost within the first weeks of a mouse's life for an yet undetermined reason, but thereafter the condition is stationary.15 Using heterozygous and homozygous Gnat1 knock-out mice, we found that the defective rod phototransduction increases the retina's susceptibility to the damaging effects of light.