【英语时差8,16】什么是卟咻症？

（单词翻译）

 The vampire¹ is the stuff of the great horror stories. However, a recent textbook by geneticist John Jenkins suggests that Bram Stoker’s legend of the vampire, Dracula, may have had its basis in a very real disease that prevents some people from getting rid of old red blood cells. In healthy people, red blood cells live only a short time and then are broken down by the body, which uses the chemical components² of old cells to make new ones. But in a hereditary³ form of a disease known as “porphyria,” a missing enzyme⁴ prevents the body from breaking down hemoglobin in old red blood cells. What happens instead is that the hemoglobin is only partially⁵ broken down, the result being some very odd symptoms.