Because XLPP is so similar to EPP, it is sometimes regarded as a variant of EPP.
Erythropoietic protoporphyria, which comprises about 90% of EPP phenotypic presentations results from inherited deficiency of the enzyme ferrochelatase (FECH). The inheritance pattern is autosomal recessive; thus, clinical manifestations occur only in people with 2 defective FECH alleles, or more commonly, one defective and one low-expressing wild-type allele.
X-linked protoporphyria, which comprises the remaining 10% of cases, results from gain-of-function mutations that increase the activity of erythroid-specific delta-aminolevulinate synthase (ALAS 2) in the bone marrow; inheritance is X-linked. The phenotype of heterozygous females can vary from asymptomatic to that of affected males.
Prevalence of EPP phenotype is about 1/75,000. Protoporphyrin accumulates in bone marrow and red blood cells, enters the plasma, and is deposited in the skin or excreted by the liver into bile. About 10% of patients develop chronic liver disease; a few of these patients develop cirrhosis, which may progress to liver failure. A more common complication is pigment gallstones due to heavy protoporphyrin excretion.
Symptom severity in erythropoietic protoporphyria and X-linked protoporphyria varies greatly, even among patients within a single family. Most patients develop symptoms in early childhood. Brief exposure to sunlight can cause severe pain, burning, erythema, and edema of the exposed skin. Usually, an infant or young child cries for hours after even short exposure to sun. Sometimes skin swelling and erythema may be subtle or absent, and EPP and XLPP may go undiagnosed longer than any other of the porphyrias.
Crusting may develop around the lips and on the back of the hands after prolonged sun exposure. However, blistering and scarring, as are typical in porphyria cutanea tarda, hereditary coproporphyria, and congenital erythropoietic porphyria (see table Some Less Common Porphyrias), do not occur.
If skin protection is chronically neglected, rough, thickened, and leathery skin (lichenification) may develop, especially over the knuckles. Linear perioral furrows (carp mouth) may develop. Patients with XLPP tend to have more severe photosensitivity and liver disease than those with EPP.
If unrecognized, erythropoietic protoporphyria and X-linked protoporphyria may cause psychosocial problems because children inexplicably refuse to go outdoors. The fear or anticipation of pain may be so distressing that children become nervous, tense, aggressive, or even develop feelings of detachment from the surroundings or suicidal thoughts.
Erythropoietic protoporphyria or X-linked protoporphyria should be suspected in children and adults with painful cutaneous photosensitivity who experience no blisters or scarring. Gallstones in children should prompt testing for EPP and XLPP. Family history is usually negative.
The diagnosis is confirmed by finding increased red blood cell and plasma protoporphyrin levels. Red blood cell protoporphyrin should also be fractionated to determine the proportions of metal-free and zinc protoporphyrin. In EPP, the proportion of red blood cell protoporphyrin that is metal-free is almost always > 85%. The presence of > 15% zinc protoporphyrin suggests XLPP.
If measured, plasma coproporphyrin and urinary porphyrin levels are normal. Stool protoporphyrin may be elevated, but coproporphyrin level is normal.
Potential carriers among relatives can be identified by finding increased red blood cell protoporphyrin levels and by genetic testing if a mutation has been identified in the index case.
Avoidance of sun exposure through use of protective clothing and opaque sunscreens
Afamelanotide for prevention of phototoxic events and relief of symptoms
Symptomatic treatment for skin burning with cold compresses, nonsteroidal anti-inflammatory drugs (NSAIDs), and topical and/or oral corticosteroids
Sometimes oral beta-carotene for prevention
Management of hepatobiliary complications
Treatment for erythropoietic protoporphyria and X-linked protoporphyria is similar. Patients with erythropoietic protoporphyria or X-linked protoporphyria should avoid sun exposure; protective clothing, hats, and light-opaque titanium dioxide or zinc oxide containing sunscreens should be used.
Afamelanotide, a long-acting congener of melanocyte stimulating hormone, which can be administered once every 60 days as a subcutaneous implant, decreases photosensitivity, allows longer exposure to light, and improves quality of life (1).
Oral beta-carotene, an antioxidant, reduces photosensitivity. However, patient adherence with beta-carotene is often poor because it is not very effective in controlling symptoms and also causes orange skin pigmentation; thus it is often tried but usually not continued. Beta-carotene dose depends on patient’s age (see table Doses of Beta-Carotene in Erythropoietic Protoporphyria).
Acute skin symptoms can be alleviated by cold baths or wet towels, analgesics, and topical and/or oral corticosteroids. Symptoms can take up to a week to resolve. If these measures are ineffective (eg, patients have increasing photosensitivity, rising porphyrin levels, progressive jaundice), giving hematin and/or red blood cell hypertransfusion (ie, to above-normal hemoglobin levels) may reduce protoporphyrin overproduction. Administration of bile acids may facilitate biliary excretion of protoporphyrin. Oral cholestyramine or charcoal have been used to interrupt the enterohepatic circulation of protoporphyrin and increase fecal excretion.
Patients who develop decompensated end-stage liver disease require liver transplantation. As with acute intermittent porphyria, patients with EPP are not eligible for standardized Model for End-Stage Liver Disease (MELD)-exception points. However, liver transplantation does not correct the underlying metabolic defect and EPP hepatopathy often develops in the transplanted liver.
Hematopoietic stem cell transplantation is curative for EPP but is not routinely done because the risk typically outweighs the benefits. The strategy of hematopoietic stem cell transplantation after liver transplantation cures EPP and prevents recurrent EPP from damaging the allograft, but the optimal timing of this strategy has not been established. Patients should be protected from operating lights during liver transplantation or other prolonged surgery to avoid serious phototoxic injury to internal organs. Light sources should be covered with commercially available filters that block wavelengths ~380 to 420 nm. Endoscopy, laparoscopy, and brief (< 1.5 hour) abdominal surgery do not usually cause phototoxic damage.
Doses of Beta-Carotene in Erythropoietic Protoporphyria and X-Linked Protoporphyria
Regular physician-patient consultations that provide information, discussion, and opportunities for genetic counseling together with physical checkups are important. Liver function and red blood cell and plasma protoporphyrin levels should be checked annually. Patients with abnormal liver function test results should be evaluated by a hepatologist; a liver biopsy may be needed to stage the degree of fibrosis. Patients with known chronic liver disease should undergo screening ultrasonography every 6 months to check for hepatocellular carcinoma.
Vitamin D levels should be checked because deficiency is common (patients tend to avoid sun exposure); supplements are given if levels are low.
Erythropoietic protoporphyria (EPP) causes severe pain, burning, erythema, and edema of exposed skin even after only brief exposure to sunlight; symptoms are not brought on by drugs that trigger other porphyrias.
Cirrhosis develops in about 10% of patients, sometimes progressing to liver failure.
Measure red blood cell and plasma protoporphyrin levels.
Prevent symptoms by avoiding sun exposure and sometimes using drugs (eg, beta-carotene, afamelanotide).
Hematin and/or red blood cell hypertransfusion may reduce protoporphyrin overproduction.
X-linked protoporphyria (XLPP) is clinically similar to EPP, but photosensitivity and liver disease are more severe than in EPP.
A useful clue for XLPP is a high proportion of red blood cell protoporphyrin that is zinc protoporphyrin.
Management of XLPP is similar to that of EPP.
The following are some English-language resources that may be useful. Please note that The Manual is not responsible for the content of these resources.
American Porphyria Foundation: Aims to educate and support patients and families affected by porphyrias and to support research into treatment and prevention of porphyrias
American Porphyria Foundation: Safe/Unsafe Database: Provides an up-to-date list of drugs available in the United States to assist physicians in prescribing for patients with porphyrias
European Porphyria Network: Promotes clinical research about porphyrias
The Drug Database for Acute Porphyrias: Provides an up-to-date list of drugs available in Europe to assist physicians in prescribing for patients with porphyrias