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A Los Angeles investigator's study of families with erythropoietic protoporphyria (EP), an inherited photocutaneous disorder first described in 1961, suggests there are two sites for abnormal protoporphyrin formation; one is erythropoietic and the other probably hepatic. The two sites apparently can function independently of each other.
"The hepatic site appears to be the source of the increased plasma protoporphyrin which seems requisite for photosensitivity to occur," Allan G. Redeker, MD, Department of Medicine, University of Southern California Medical School, told the American College of Physicians. Redeker said that protoporphyrin has been found in the plasma of all his EP patients "and seems clearly to be the photosensitizing agent."
In one EP family, in which fraternal twin boys have the disease, the mother, who has never had a cutaneous lesion, does, however, have a large increase in her fecal protoporphyrin excretion. "This apparent evidence of a latent trait suggests a dissociation
EP Study Indicates Two Sites For Abnormal Protoporphyrin. JAMA. 1964;190(5):34. doi:10.1001/jama.1964.03070180090048