GUCY2D was the first gene to be associated with LCA/EOSRD and is one of the most common, accounting for approximately 10%–20% of cases.16GUCY2D is known to encode retinal guanylate cyclase-1 (RetGC1), expressed in photoreceptor outer segments, to a greater degree in cones than rods.23 24 RetGC1 is known to play an important role in photoreceptor recovery following phototransduction, thereby disease-causing variants in GUCY2D and subsequent RetGC1 deficiency result in the biochemical equivalent of chronic light exposure.16 Here, GUCY2D is linked to severe early-childhood-onset retinal dystrophy.