Porphyria is a genetic disorder. In one form, affected people lack enzymes of a metabolic pathway that forms heme, the iron-containing group in hemoglobin. Chemicals called porphyrins accumulate and cause terrible symptoms, especially if the person is exposed SPL/Science Source to sunlight. Sores and scars form on the skin (Figure 4.18). The gums shrink away from the teeth and the canine teeth may begin to look like fangs. Drinking alcohol or eating garlic makes symptoms worse. People with porphyria can avoid sunlight and aggravating substances. They also can get injections of heme from normal red blood cells. If you are familiar with vampire stories, which date from centuries ago, can you think of a reason why they may have arisen among people who knew nothing about the cause of porphyria?

Figure 4.18