Heme synthesis - note that some reactions occur in the cytoplasm and some in the mitochondrion (yellow)
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Porphyria

The porphyrias are inherited or acquired disorders of certain enzymes in the heme biosynthetic pathway (also called porphyrin pathway). They are broadly classified as hepatic porphyrias or erythropoietic porphyrias, based on the site of the overproduction and mainly accumulation of the porphyrins (or their chemical precursors). more...

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Overview

In humans, porphyrins are the main precursors of heme, an essential constituent of hemoglobin, myoglobin, and cytochrome.

Deficiency in the enzymes of the porphyrin pathway leads to insufficient production of heme. This is, however, not the main problem; most enzymes—even when less functional—have enough residual activity to assist in heme biosynthesis. The largest problem in these deficiencies is the accumulation of porphyrins, the heme precursors, which are toxic to tissue in high concentrations. The chemical properties of these intermediates determine in which tissue they accumulate, whether they are photosensitive, and how the compound is excreted (in the urine or feces).

Subtypes

There are eight enzymes in the heme biosynthetic pathway: the first and the last three are in the mitochondria, while the other four are in the cytosol.

  1. δ-aminolevulinate (ALA) synthase
  2. δ-aminolevulinate (ALA) dehydratase
  3. hydroxymethylbilane (HMB) synthase
  4. uroporphyrinogen (URO) synthase
  5. uroporphyrinogen (URO) decarboxylase
  6. coproporphyrinogen (COPRO) oxidase
  7. protoporphyrinogen (PROTO) oxidase
  8. ferrochelastase

Hepatic porphyrias

The hepatic porphyrias include:

  • ALA dehydratase deficiency
  • acute intermittent porphyria (AIP): a deficiency in HMB synthase
  • hereditary coproporphyria (HCP): a deficiency in COPRO oxidase
  • variegate porphyria (VP): a deficiency in PROTO oxidase
  • porphyria cutanea tarda (PCT): a deficiency in URO decarboxylase

Erythropoietic porphyria

The erythropoietic porphyrias include:

  • X-linked sideroblastic anemia (XLSA): a deficiency in ALA synthase
  • congenital erythropoietic porphyria (CEP): a deficiency in URO synthase
  • erythropoietic protoporphyria (EPP): a deficiency in ferrochelatase

Porphyria variegata

Variegate porphyria (also porphyria variegata or mixed porphyria) results from a partial deficiency in PROTO oxidase, manifesting itself with skin lesions similar to those of porphyria cutanea tarda combined with acute neurologic attacks. It may first occur in the second decade of life; there is a cohort of sufferers living in South Africa descended from a single person from the Netherlands, Berrit Janisz, who emigrated in the 17th century.

Signs and symptoms

The hepatic porphyrias primarily affect the nervous system, resulting in abdominal pain, vomiting, acute neuropathy, seizures, and mental disturbances, including hallucinations, depression, anxiety, and paranoia. Cardiac arrhythmias and tachycardia (fast heart rate) may develop as the autonomic nervous system is affected. Pain can be severe and can, in some cases, be both acute and chronic in nature. Constipation is frequently present, as the nervous system of the gut is affected.

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Anaesthesia is also risky in patients with porphyria - Letter to the Editor
From British Medical Journal, 10/21/00 by Susan deC Baker

EDITOR--Thadani et al, in their review of the diagnosis and management of porphyria, comment on the risk of surgery but place insufficient emphasis on the potential hazards of anaesthesia for this group of patients.[1] For patients with porphyria, anaesthesia carries a significant risk of morbidity and mortality, although most can now have surgery with comparative safety as a result of modern techniques in anaesthesia and the development of pharmacological agents with shorter half lives.[2-5] Further improvements in anaesthesia safety depend on earlier detection of susceptible patients and the identification of potentially porphyrinogenic agents, neither of which may be readily achievable. Any patient with proved or suspected porphyria should be referred for early anaesthetic assessment if surgery is contemplated.

Susan deC Baker anaesthetic senior house officer HaHara@aol.com

Bruce Taylor consultant Department of Anaesthesia, Queen Alexandra Hospital, Portsmouth PO19 4SE

[1] Thadani 14, Deacon A, Peters T. Diagnosis and management of porphyria. BMJ 2000;320:1647-50. (17 June.)

[2] Harrison GG, Meissner PN, Hift RJ. Anaesthesia for the porphyric patient. Anaesthesia 1993;48:417-21.

[3] James MFM, Hift RJ. Porphyrias. Br J Anaesthesia 2000;85:143-53.

[4] Jensen NF, Fiddler DS, Striepe V. Anaesthetic considerations in porphyrias. Anaesth Analg 1995;80:591-9.

[5] Ashley EM. Anaesthesia for porphyria. Br J Hosp Med 1996;56:37-42.

COPYRIGHT 2000 British Medical Association
COPYRIGHT 2000 Gale Group

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