RHO and retinitis pigmentosa: Rod photoreceptors show abnormal neurite sprouting in humans with retinitis pigmentosa (Li et al., 1995; Milam and Li, 1996; Fariss et al., 2000), cats with rod/cone dysplasia (Chong et al., 1999), and pigs carrying a mutation in the rhodopsin gene (Li et al., 1998).