NORD gratefully acknowledges Ashwani K Singal, MD, MSc, Division of Gastroenterology and Hepatology, University of Alabama at Birmingham, for assistance in the preparation of this report.
Hepatoerythropoietic porphyria (HEP) is an extremely rare genetic disorder characterized by deficiency of the enzyme, uroporphyrinogen decarboxylase. This deficiency is caused by mutations of both copies of a person’s UROD gene, which means that the disorder is inherited as an autosomal recessive trait. Most affected individuals have a profound deficiency of this enzyme and onset of the disorder is usually during infancy or early childhood. However, some individuals may have a mild form that can go undiagnosed until adulthood. The childhood form of HEP is often associated with painful, blistering skin lesions that develop on sun-exposed skin (photosensitivity). Affected areas of skin can scar and become discolored. There may be risk of bacterial infection. Abnormal, excessive hair (hypertrichosis) on affected skin is also common. Mild anemia and abnormal enlargement of the liver and/or spleen (hepatosplenomegaly) have also been reported. Mild cases of HEP may go unrecognized until adulthood and can be clinically indistinguishable from porphyria cutanea tarda (PCT), a related disorder that may be acquired or occur in individuals with a mutation of one UROD gene (autosomal dominant inheritance). Cutaneous photosensitivity is generally much more severe in HEP than in PCT. NORD has a separate report on porphyria cutanea tarda.Introduction
HEP belongs to a group of disorders known as the porphyrias. This group of at least seven disorders is characterized by abnormally high levels of porphyrins and porphyrin precursors due to deficiency of certain enzymes essential to the creation (synthesis) of heme, a part of hemoglobin and other hemoproteins. There are eight enzymes in the pathway for making heme and at least seven major forms of porphyria. The symptoms associated with the various forms of porphyria differ. It is important to note that people who have one type of porphyria do not develop any of the other types. Porphyrias are generally classified into two groups: the "hepatic" and "erythropoietic" types. Porphyrins and porphyrin precursors and related substances originate in excess amounts predominantly from the liver in the hepatic types and mostly from the bone marrow in the erythropoietic types. Porphyrias with skin manifestations are sometimes referred to as "cutaneous porphyrias". The term "acute porphyria" is used to describe porphyrias that can be associated with sudden attacks of pain and other neurological symptoms. HEP is a hepatic and cutaneous porphyria.
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