Proto-oncogene c-Mer (C-mer) is a cell entry factor for filovirus. C-mer is not e, Xenopus/Amphibian,pressed in normal B- and T-lymphocytes but is e, Xenopus/Amphibian,pressed in numerous neoplastic B- and T-cell lines. Defects in C-mer are a cause of retinitis pigmentosa (RP) that leads to degeneration of retinal photoreceptor cells. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well.