Decreased CTBP2 immunoreactivity was evident by 6 months post fertilization, before other obvious signs of retinal degeneration such as photoreceptor outer segment loss were seen, and was correlated with an increase in size and number of disorganized photoreceptor ribbon synapses in the cone pedicles of aging frogs as observed with TEM in 8-month-old frogs (Fig. 8A; Fig. S4). The gene discussed is CTBP2; the disease is retinal degeneration.