Erythropoietic protoporphyria (EPP) is a human genetic/metabolic disorder in which accumulation of the compound protoporphyrin causes skin sensitivity to sunlight. Some individuals with the disorder also have mild anemia, and a few have hepatobiliary disease. Iron is joined to protoporphyrin to form heme in the mitochondria of cells, under control of the enzyme ferrochelatase. Defects in this process cause the accumulation of protoporphyrin, leading to the biochemical and clinical features of EPP. Abnormalities in the ferrochelatase gene are the major cause of the defect, but do not satisfactorily explain the severity of the phenotype in all subjects. Mitoferrin-1 transports iron to ferrochelatase in the mitochondria of cells for heme formation, and also transports iron for the formation of a compound that keeps ferrochelatase active and stable. Thus, a deficiency of this iron transporter could reduce ferrochelatase activity and contribute to the phenotype in EPP.