The Vampires in True Blood attribute the cause of their vampirness with a disease. This actually rings true. Porphyria is a rare disease that is apart of the Vampire Legends.
Vampire characteristics are similar to those of porphyrics and this may have led to the misconception in the early 1400-1600′s that porphyria sufferers were vampires. Vampire legends are in every country and porphyria is also found throughout the world. Porphyria comes from the Greek word meaning purple.
According to associated content porphyria is a group of disorders caused by the abnormal production of heme which is the base material responsible for making hemoglobin and chlorophyll. Most types of porphyria are inherited. A child needs to inherit the defective gene from only one parent to develop the disease. Heme is a substance found in all body tissues. Excessive porphyrin in the body causes photosensitivity which is oversensitivity to sunlight(explaing why vampires can’t go out in the sunglight). When porphyrins are exposed to light and oxygen, they generate a charged, unstable form of oxygen that can damage the skin. Nerve damage, pain and paralysis can occur in some porphyrias.
In addition, haemtodipsia is a documented medical disorder, which is a sexual thirst for blood and heeralopia or day blindness. Anemia (bloodlessness) was often in the early centuries mistaken for a vampire bite.