Porphyrias, a group of eight known blood disorders, affect the body's molecular machinery for making heme, which is a component of the oxygen-transporting protein, hemoglobin. When heme binds with iron, it gives blood its hallmark red color. The different genetic variations that affect heme production give rise to different clinical presentations of porphyria -- including one form that may be responsible for vampire folklore. Erythropoietic protoporphyria (EPP), the most common kind of porphyria to occur in childhood, causes people's skin to become very sensitive to light. Prolonged exposure to sunshine can cause painful, disfiguring blisters. "People with EPP are chronically anemic, which makes them feel very tired and look very pale with increased photosensitivity because they can't come out in the daylight," says Barry Paw MD, PhD, 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." Staying indoors during the day and receiving blood transfusions containing sufficient heme levels can help alleviate some of the disorder's symptoms. 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. Now, Dr. Paw and his team of international investigators report -- in a paper published online on September 5, 2017 in PNAS -- a newly discovered genetic mutation that triggers EPP.
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