Constitutive signaling, increased retinal oxygen, and altered retinoic acid concentrations are responsible, in part or in combinations, for retinal degenerations resulting from vitamin A deficiency, constant light exposure, Leber congenital amaurosis, congenital night blindness, RPB4 deficiency, and retinitis pigmentosa. This evidence concerns the gene POLR2D and hyperinsulinemic hypoglycemia, familial, 4.