Erythropoietic protoporphyria is a type of porphyria. Porphyrias are caused by an abnormality in the heme production process. Heme is essential in enabling our blood cells to carry oxygen and in breaking down chemical compounds in the liver. Erythropoietic protoporphyria is caused by impaired activity of ferrocheletase, an important enzyme in heme production. This results in the build-up of protoporphyrin in the bone marrow, red blood cells, blood plasma, skin, and eventually liver. Build up of protoporphyrin can cause extreme sensitivity to sunlight, liver damage, abdominal pain, gallstones, and enlargement of the spleen. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.