A disorder of porphyrin metabolism in which there is excessive accumulation of protoporphyrin in the body; specifically (more fully "erythropoietic protoporphyria") an inherited (autosomal dominant) disorder in which reduced activity of the mitochondrial enzyme ferrochelatase causes accumulation of protoporphyrin IX in erythrocytes, hepatocytes, and serum, leading to photosensitivity of the skin and, often, liver disease.