Porphyrias

What is Porphyrias ?

Porphyrias is an umbrella term for metabolic disorders that affect the biosynthesis of heme (a component of hemoglobin) and cause excessive production and excretion of porphyrins or their precursors. Porphyrins, which are present in all protoplasm, playa role in energy storage and use. The classification of porphyrias depends on the site of excessive porphyrin production: They may be erythropoietic (erythroid cells in bone marrow), hepatic (in the liver), or erythrohepatic (in bone marrow and liver).

Causes of Porphyrias

Porphyrias are inherited as autosomal dominant traits, except for Gunther's disease, which is an autosomal recessive trait, and toxic-acquired porphyria, which usually results from lead ingestion or lead exposure. Enzymatic defects occurring in the heme synthetic pathway cause porphyrias.

Signs & Symptoms of Porphyrias

Porphyria Symptoms & Signs include:

• Skin swelling on exposure to sunlight
• Pain in the limbs
• Blister (bulla) formation on exposure to sunlight
• Muscle weakness or paralysis
• Vomiting
• Red urine
• Chest pain
• High blood pressure
• Rapid pulse
• Skin blisters Hair growth abnormalities
• Skin pigment changes

Diagnostic Tests

In acute intermittent porphyria, the Watson-Schwartz test result may be positive for porphobilinogen in the urine; the ion exchange chromatography test may identify aminolevulinic acid (ALA) in the urine.

In variegate porphyria. protoporphyrin and coproporphyrin may be positive in the stools. With hereditary coproporphyria, large amounts of coproporphyrin appear in the stools and, to a lesser extent, in the urine.

Porphyria cutanea tarda results in increased excretion of uroporphyrins; the amount of fecal porphyrins varies.

Treatment

Depending on the type of porphyria, treatment may include the administration of beta carotene to reduce photosensitivity, chlorpromazine I.V. to treat mild abdominal discomfort, meperidine to treat severe pain, levulose I.V. to increase carbohydrate intake, and hemin (an enzyme inhibitor derived from processed red blood cells) to suppress hepatic ALA and porphobilinogen. Splenectomy may be performed to treat hemolytic anemia. Patients with photosensitivity should avoid direct sunlight or use sunscreen preparations. A high carbohydrate level with restricted fluid intake decreases urinary excretion of the enzymes 5-ALA synthase and hydroxymethylbilane (also called HMB, porphobilinogen, deaminase, uroporphyrinogen I synthase), inhibiting the release of antidiuretic hormone.

Prevention Tips

Genetic counseling may be of benefit to prospective parents with a family history of any type of porphyria.