Hepatoerythropoietic Porphyria (HEP)

Pathophysiology and Genetics

Severe Loss of UROD Enzyme Activity

UROD catalyzes the four-step decarboxylation of uroporphyrinogen III to coproporphyrinogen III in the heme biosynthesis pathway.

• In HEP: The patient inherits a mutated UROD allele from each parent. Together they severely distort the enzyme, wiping out almost all of its function (activity falls below 10% and is sometimes undetectable).
• Backlog and diverted metabolism: With the pathway severely blocked at the UROD step, uroporphyrinogen I and III pile up to very high levels in the liver and reticulocytes.
• Zinc protoporphyrin (ZPP) accumulation: A hallmark that separates HEP from PCT is a very high level of zinc protoporphyrin in red cells. Faced with heme shortage, the body responds by having ferrochelatase insert zinc (Zn2+) into protoporphyrin IX.

Phototoxicity and Hemolytic Anemia

• Deposition in the skin: Water-soluble uroporphyrin travels from the liver and marrow into the bloodstream and settles in the basement membrane and superficial dermal capillaries.
• Activation in the Soret band (400–410 nm): On exposure to blue-violet visible light, uroporphyrin molecules absorb energy at their peak, enter an excited state and generate potent oxidants (singlet oxygen and other reactive oxygen species, ROS).
• Tissue necrosis and hemolysis: ROS damage endothelial cell membranes and type IV/VII collagen, and directly injure porphyrin-laden red cells as they pass through light-exposed superficial capillaries, causing normochromic hemolytic anemia.

Distinguishing Features: HEP vs. PCT Type II vs. CEP

To avoid confusing the porphyrias that cause severe skin disease, the table below sets out the key differences:

Characteristic Clinical Features of HEP

Unlike PCT, which starts in adulthood, HEP shows up very early, often within the first few months after birth or during the first 2–3 years of life.

Destructive Photocutaneous Lesions

• Red urine from birth: Parents often notice dark red, wine-colored or strong tea-colored diapers from very early on, because of uroporphyrin excretion.
• Widespread blisters and erosions: From the very first sun exposure, tense blisters form and rupture easily, leaving painful shallow ulcers on the face, backs of the hands, forearms and feet.
• Deforming scars and contractures: Repeated injury from early childhood leaves exposed skin heavily scarred:
  • Facial deformity: Loss of nasal cartilage, shrunken ears and lip retraction that exposes the teeth.
  • Finger contractures and mutilation: Thinning of the finger skin, stiff joints, claw-like deformity and loss of the distal finger segments (dactylolysis).
• Pigment changes and dense hair growth: Extensive hypertrichosis over the face, forehead, temples and limbs, with mottled patches of increased and decreased pigmentation.

Systemic and Blood Manifestations

• Chronic hemolytic anemia: Pallor and fatigue from peripheral destruction of porphyrin-laden red cells.
• Splenomegaly: The spleen works harder and enlarges as it constantly clears damaged red cells containing zinc protoporphyrin.
• Liver involvement: Long-term uroporphyrin buildup in the liver can lead to fibrosis and declining liver function over time.

Confirming the Diagnosis: Biochemical and Genetic Testing at Haute-Derma

A definitive diagnosis of HEP requires both specific porphyrin measurements and genetic testing.

Porphyrin Analysis of Biological Samples

• Red blood cells: The most important test. It shows a sharp rise in zinc protoporphyrin (ZPP), the biochemical key that rules out ordinary PCT.
• Urine: Uroporphyrin (particularly uroporphyrin I and III) is tens to hundreds of times above normal.
• Stool: Raised isocoproporphyrin and pentacarboxyporphyrin.

Enzyme Activity and Genetics

• UROD enzyme assay: UROD activity is measured in red cell lysate or fibroblasts and confirms activity below 10% of normal.
• UROD gene sequencing: Looks for deletions, nonsense mutations or frameshift mutations on both alleles of UROD.
• Family screening: Both parents of a child with HEP carry one mutated copy (heterozygous) and usually have no symptoms or only mild PCT type II.

Management and Treatment Strategy at Haute-Derma

Unlike PCT, which can respond well to phlebotomy or hydroxychloroquine, HEP does not respond to either, because UROD activity is almost entirely lost. Treatment focuses on symptom control, rigorous skin protection and hematologic support.

Controlling Phototoxicity and Protecting the Skin

• Strict avoidance of visible light:
  • Ordinary sunscreens do not help. Patients need dedicated light filters and a thick layer of mineral sunscreen containing iron oxide plus zinc oxide to block the Soret band (400–410 nm).
  • Window film that blocks UV and blue-violet visible light at home, at school and in the car.
  • UPF 50+ protective clothing, gloves, a wide-brimmed hat and sunglasses outdoors.
• Wound care and infection prevention:
  • Blisters are cleaned with a gentle antiseptic and covered with non-stick petrolatum gauze.
  • Topical or oral antibiotics are started at the first sign of secondary infection to prevent deep necrosis and loss of finger segments.

Managing Systemic Complications

• Hematologic support:
  • Regular monitoring of blood counts, iron, ferritin and hemoglobin.
  • Red cell transfusion for severe hemolytic anemia.
• Considering splenectomy: Indicated for prolonged, severe hemolysis with a markedly enlarged spleen causing significant drops in platelets or white cells.
• Protecting liver function: Strict avoidance of liver-toxic drugs and alcohol, and full vaccination against hepatitis A and B.

Emerging Therapies

• Gene therapy: Introducing a healthy UROD gene into blood-forming stem cells is the most promising research avenue for restoring UROD production at its source.
• Hematopoietic stem cell transplantation (HSCT): Has been considered experimentally in a few HEP patients with severe marrow involvement and hemolysis, to replace the mutated red cell line.