Scientists in the US have pinpointed the gene believed to be behind the vampire myth.
For centuries, cultures across the world have told tales of pale-skinned beings with a ravenous appetite for blood who avoid the sunlight.
The word 'vampire' itself first appeared in English in the early 1700s, and became widely known following the publication of Bram Stoker's 1897 novel Dracula.
Researchers at Boston Children's Hospital now say they've isolated the gene responsible for a blood disorder whose symptoms "may be responsible for vampire folklore".
Porphyrias is a group of eight related blood disorders. Though rare, the most common - erythropoietic protoporphyria (EPP) - causes people's skin to break out in painful blisters if they get too much sunlight.
"People with EPP are chronically anaemic, which makes them feel very tired and look very pale with increased photosensitivity because they can't come out in the daylight," says Dr Barry Paw of the Dana-Farber/Boston Children's Cancer and Blood Disorders Center.
"Even on a cloudy day, there's enough ultraviolet light to cause blistering and disfigurement of the exposed body parts, ears and nose."
EPP also prevents the body making enough of a substance called heme, which protects the skin from the sun's rays.
"Staying indoors during the day and receiving blood transfusions containing sufficient heme levels can help alleviate some of the disorder's symptoms," Dr Paw said.
"In ancient times, drinking animal blood and emerging only at night may have achieved a similar effect - adding further fuel to the legend of vampires."
The researchers found the gene responsible after examining a family from northern France. It opens the door to new treatments for the disorder.
"Although vampires aren't real, there is a real need for innovative therapies to improve the lives of people with porphyrias," says Paw.
The research was published in journal Proceedings of the National Academy of Sciences.