GUCY2EP and Abnormal retinal morphology: Of the 75 genes associated with retinitis pigmentosa, 12 were differentially expressed during spaceflight (Sag, BC027072/Pcare, Guca1b, Rbp3, Ahi1, Guca1a, Prpf8, Rp1, Gucy2e, Cacna2d4, Pde6b, Dhdds), the most of any of the four retinal diseases examined.