A) certain brain cells have many extra orexin/hypocretin receptors, so that the cell receives too many messages to sleep. B) the orexin/hypocretin receptor is missing, abnormal in structure, or unable to move to the surface of certain brain cells, blocking signals to stay awake. C) a gene is missing in chromosome 6 that encodes the protein narcoleptin. D) a viral infection activates genes that promote sleep. E) four key genes are overexpressed.