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4月25日 雨
纯粹看到想要分享的文章。
记录下来。
The Myth of Vampires and Porphyria
It is always interesting to speculate on the origin of a folkloric tale, especially one that is as widespread as that of the blood sucking creature of the night known as the vampire. Many societies have tales of the undead who come back from the great beyond to torment the living, but our image of the vampire is generally based on Bela Lugosi’s portrayal of Bram Stoker’s sanguinary count. Dracula had a pale complexion, was sensitive to sunlight, feared garlic, and had to sustain himself by drinking human blood, preferably tapping the neck of pretty young things. In 1985, University of British Columbia’s Dr. David Dolphin, who was to become one of Canada’s top chemists, mused that perhaps the legend of the vampire could be traced to people suffering from porphyria.
The idea was not novel, in 1963 the Proceedings of the Royal Society of Medicine had already featured a paper entitled “On Porphyria and the Aetiology of Werewolves.” Dolphin described porphyria victims’ sensitivity to sunlight, and the possibility that receding gums can give the appearance of fangs. He also suggested that garlic contains a chemical that makes the condition worse, and that while porphyria now is treated by injection of blood products such as hematin that interfere with porphyrin synthesis, at one time victims may have attempted self-treatment by drinking blood. It all amounted to interesting, somewhat whimsical, speculation. But the press ignored the “ifs,” “buts” and “maybes,” and concluded that not only vampire, but also werewolf legends, were based on the afflictions of porphyria. After all, who doesn’t love a good vampire or werewolf story?
There is just one little problem with the vampire-porphyria hypothesis. It really doesn’t hold up to scientific scrutiny. Porphyria is real enough, but it has nothing to do with vampires. Actually, porphyria is not one disease, but a group of rare genetic blood disorders characterized by the buildup of molecules called porphyrins in the body. Porphyrins are precursors to hemoglobin, the oxygen carrying compound in red blood cells. In the porphyrias, due to enzyme irregularities, porphyrins are synthesized, but are not incorporated into hemoglobin and consequently build up in tissues, and in some cases even in teeth. Porphyrins readily absorb both visible and ultraviolet light and transfer the energy to oxygen molecules to form singlet oxygen, an extremely energetic form of oxygen. It is the action of this highly reactive species on tissues that causes the symptoms of porphyria. The term derives from the Greek for “purple pigment,” since victims often present with a purplish discoloration of the urine and feces due to the excretion of colored porphyrins. Buildup of porphyrins in the teeth can cause an eerie reddish fluorescence, perhaps giving the appearance of remnants of blood. Other symptoms include pain, blisters and skin degeneration due to photosensitivity, and occasionally increased hair growth on the forehead.
The type of porphyria that can cause serious gum and skin disfigurement, congenital erythropoetic porphyria, is extremely rare, with only some 200 cases ever having been diagnosed. Victims do not crave blood, and in any case, ingested blood would be of no help for treatment of the disease. And the garlic? Well those of you keep garlic around I’m sure will attest to the fact that you have never been visited by a vampire. But what about a porphyria link? That suggestion revolves around hemoglobin, the oxygen-carrying compound in blood. Allyl disulfide, one of many compounds found in garlic, activates an enzyme that destroys hemoglobin by removing iron from the molecule. Since porphyria victims already have poorly functioning red blood cells, the argument goes, in theory they should have a problem with garlic. While it is true that in porphyria there is a problem with hemoglobin synthesis, there is still no shortage of this compound in red blood cells. The problem in the porphyrias isn’t lack of hemoglobin, it is the accumulation of tissue damaging porphyrins. In any case, there is no evidence at all that real porphyria patients have anything to fear from garlic. They do, however, have something to fear from stories that add to the burden of their disease by associating them with vampires. Perhaps it is time to drive a wooden stake through the heart of any speculation that vampires are really victims of porphyria. |
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