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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Dobson's Complaint: The Story of the Chester Porphyria - Review
From British Medical Journal, 1/30/99 by Helen Crimlisk

Dobson's Complaint: The Story of the Chester Porphyria Ed Giles R Youngs

Royal College of Physicians, 18.50 [pounds sterling], pp 200 ISBN 1 86016 047 6

Rating: ***

There are many aspects of medical disorders that fascinate doctors: the application of the latest scientific techniques, complex biochemical mechanisms, the detective work involved in teasing out a complex history, the personal strengths that emerge when tragedy strikes, and the thrill of finding a new disorder. This book covers all these features and more about one of the rarer variants of porphyria--Chester porphyria, which results from a combination of the deficits found in the commoner acute intermittent porphyria and variegate porphyria. Although concentrating on this variant, the book also provides an overview of the porphyrias in general.

Giles Youngs, a physician in Chester, tells the story of the painstaking work of himself and his past juniors (who have contributed to many aspects of the research in this book). They traced back members of the 300 strong Cheshire kindred affected by this condition to the marriage of a Dee salmon fisherman in 1888. Youngs is brutally honest about how he was initially shamed by one of the family--who clearly knew more than he did about the nature of the curse responsible for wiping out large swathes of her family--into starting his mammoth task, which clearly became a labour of love as time progressed. He pays due debt to the doctors who preceded him, in particular to Dr Zorka Bekerus, who in 1965 was the first to recognise the uniqueness of this variant of porphyria.

The monograph is comprehensive in its coverage of all the aspects of this disorder. Individual chapters stand alone--indeed, several are transcripts of previously published work--and this inevitably leads to a degree of repetition and some contradiction. Nevertheless, the advantage of this arrangement is that the book can easily be browsed and used as a reference for the genetics and biochemistry of this disorder as well as the clinical features. These include neurological and psychiatric disturbances, hyponatraemia, and the hypertension and renal failure that have been responsible for so much of the mortality in the Chester kindred.

Youngs has traced the death certificates and case notes of long dead members of the families, identifying with the benefit of hind-sight the errors made by previous generations of doctors. He avoids, however, any sense of triumphalism and never loses sight of the personal tragedy that obviously still haunts the family.

My only criticism is that no room was found for the family's voice. As with porphyria kindreds elsewhere, morbidity and mortality have been reduced by better diagnostic techniques, avoidance of precipitants (especially barbiturates and other drugs), and treatment of accompanying hypertension. However, family members continue to live with the burden of a rare genetic disorder, one described as the "little imitator" because of the multitude of symptoms, which often led sufferers to be misdiagnosed as "hysterics" With this background, they must have a fascinating perspective, which would have complemented this enthralling book.

Helen Crimlisk, trainee in child psychiatry, University of Marburg, Germany

COPYRIGHT 1999 British Medical Association
COPYRIGHT 2000 Gale Group

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