Vampires!

Porphyrias are diseases that result from disordered enzymes in heme biosynthesis (making hemoglobin for red blood cells). Porphyria cutanea tarda is one of these diseases, and its most striking manifestation is a sensitivity to sunlight. When exposed to sun, patients with the disease will have blistering, scarring, changes in pigmentation, and hair growth. Other symptoms include necrosis of the gums and iron overload.

Thus, some have proposed that the origin of vampire legends are based on this disease. Vampires are sensitive to light. With necrosis and retraction of the gums, the canine teeth appear larger. Since those with porphyrias are anemic (due to inability to synthesize heme), they appear pale. Perhaps they can even restore their blood by getting it from other people. According to Wikipedia, porphyrias might have been more common in small Transylvanian villages than elsewhere because of inbreeding.

I guess legends have to come from somewhere, and this interested me a lot. Perhaps vampires are just fictional exaggerations of this very tragic disease. Obviously, I don't want to suggest any connection between vampires and those with porphyria other than in the origin of this tale.

(Image: Edward Munch, Vampire. There were many results when I google imaged vampire, but this one was most artistic.)