Heme synthesis - note that some reactions occur in the cytoplasm and some in the mitochondrion (yellow)
Find information on thousands of medical conditions and prescription drugs.

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...

Home
Diseases
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Arthritis
Arthritis
Bubonic plague
Hypokalemia
Pachydermoperiostosis
Pachygyria
Pacman syndrome
Paget's disease of bone
Paget's disease of the...
Palmoplantar Keratoderma
Pancreas divisum
Pancreatic cancer
Panhypopituitarism
Panic disorder
Panniculitis
Panophobia
Panthophobia
Papilledema
Paraganglioma
Paramyotonia congenita
Paraphilia
Paraplegia
Parapsoriasis
Parasitophobia
Parkinson's disease
Parkinson's disease
Parkinsonism
Paroxysmal nocturnal...
Patau syndrome
Patent ductus arteriosus
Pathophobia
Patterson...
Pediculosis
Pelizaeus-Merzbacher disease
Pelvic inflammatory disease
Pelvic lipomatosis
Pemphigus
Pemphigus
Pemphigus
Pendred syndrome
Periarteritis nodosa
Perinatal infections
Periodontal disease
Peripartum cardiomyopathy
Peripheral neuropathy
Peritonitis
Periventricular leukomalacia
Pernicious anemia
Perniosis
Persistent sexual arousal...
Pertussis
Pes planus
Peutz-Jeghers syndrome
Peyronie disease
Pfeiffer syndrome
Pharmacophobia
Phenylketonuria
Pheochromocytoma
Photosensitive epilepsy
Pica (disorder)
Pickardt syndrome
Pili multigemini
Pilonidal cyst
Pinta
PIRA
Pityriasis lichenoides...
Pityriasis lichenoides et...
Pityriasis rubra pilaris
Placental abruption
Pleural effusion
Pleurisy
Pleuritis
Plummer-Vinson syndrome
Pneumoconiosis
Pneumocystis jiroveci...
Pneumocystosis
Pneumonia, eosinophilic
Pneumothorax
POEMS syndrome
Poland syndrome
Poliomyelitis
Polyarteritis nodosa
Polyarthritis
Polychondritis
Polycystic kidney disease
Polycystic ovarian syndrome
Polycythemia vera
Polydactyly
Polymyalgia rheumatica
Polymyositis
Polyostotic fibrous...
Pompe's disease
Popliteal pterygium syndrome
Porencephaly
Porphyria
Porphyria cutanea tarda
Portal hypertension
Portal vein thrombosis
Post Polio syndrome
Post-traumatic stress...
Postural hypotension
Potophobia
Poxviridae disease
Prader-Willi syndrome
Precocious puberty
Preeclampsia
Premature aging
Premenstrual dysphoric...
Presbycusis
Primary biliary cirrhosis
Primary ciliary dyskinesia
Primary hyperparathyroidism
Primary lateral sclerosis
Primary progressive aphasia
Primary pulmonary...
Primary sclerosing...
Prinzmetal's variant angina
Proconvertin deficiency,...
Proctitis
Progeria
Progressive external...
Progressive multifocal...
Progressive supranuclear...
Prostatitis
Protein S deficiency
Protein-energy malnutrition
Proteus syndrome
Prune belly syndrome
Pseudocholinesterase...
Pseudogout
Pseudohermaphroditism
Pseudohypoparathyroidism
Pseudomyxoma peritonei
Pseudotumor cerebri
Pseudovaginal...
Pseudoxanthoma elasticum
Psittacosis
Psoriasis
Psychogenic polydipsia
Psychophysiologic Disorders
Pterygium
Ptosis
Pubic lice
Puerperal fever
Pulmonary alveolar...
Pulmonary hypertension
Pulmonary sequestration
Pulmonary valve stenosis
Pulmonic stenosis
Pure red cell aplasia
Purpura
Purpura, Schoenlein-Henoch
Purpura, thrombotic...
Pyelonephritis
Pyoderma gangrenosum
Pyomyositis
Pyrexiophobia
Pyrophobia
Pyropoikilocytosis
Pyrosis
Pyruvate kinase deficiency
Uveitis
Q
R
S
T
U
V
W
X
Y
Z
Medicines

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.

Read more at Wikipedia.org


[List your site here Free!]


Niacin, heme synthesis and porphyria - Letters to the Editor
From Townsend Letter for Doctors and Patients, 6/1/03

Editor:

The prize winning paper by Jonathon E. Prousky, ND, FRSH and Dugald Seely, BSc, ND (candidate) in the February/March 2003 issue entitled "The Case Report on the Successful Use of Inositol Hexaniacinate for the Treatment of Achiorhydria: Its Possible Mechanism of Action Upon the Central Nervous System and Parietal Cell-Adenosine Triphosphate-Dependent K+/H+ Pump" was most interesting. I would like to suggest an additional reason for the effectiveness of the high doses of niacin (1000 mg three times daily) that were used initially to treat the 39 year-old, 'well-nourished' patient. In the article, "Vitamin B-3 and Schizophrenia" by A. Hoffer, MD, PhD, FRCP(C) in the April 2001 issue, Dr. Hoffer explained that high doses of niacin change liver enzyme function, and that small elevations in liver enzyme tests were often seen with niacin therapy, but were no cause to discontinue the treatment. This change in liver enzyme activity would probably stimulate the production of much higher quantities of heme.

Heme is required for the synthesis of the P450 enzymes that are collectively responsible for the oxidation (and therefore the neutralization) of foreign chemicals, including drugs, pesticides and carcinogens. The P450 enzymes are also needed for the metabolism of adrenal hormones, fat soluble vitamins, fatty acids and for the synthesis of eicosanoids (so this includes the pro staglandins). (1,2) The correct balance and availability of adrenal hormones and also of eicosanoids control the flow of nutrients (including oxygen) into the cells. (3) Perhaps even more important, heme is needed for the production of red blood cells. (2) The consequent increase in the oxygen, and nutrient-carrying capacity of the blood, as well as the cell's renewed ability to receive the required nutrients, along with niacin's effect on the central nervous system and the parietal cells, fully restored the production of stomach acid in the 39 year-old patient.

However, the transformation of chemicals by the P450 enzymes can result in either increased or decreased toxicity, depending on the nutritional status and the toxicity of the patient. For example, low protein diets are associated with lower rates of drug metabolism. On the other hand, diets that are very low in carbohydrates deplete the necessary cofactors of P450 enzymes. (1) People with severe deficiencies from low stomach acidity and stress or toxicity are especially vulnerable when the liver and its enzymes are overtaxed. (1,2)

Very high doses of niacin (3,000 mg or more daily) can cause liver damage, diabetes, an inflamed stomach, eye damage and elevated levels of uric acid which can cause gout. The inositol hexaniacinate form of niacin is not known to cause any side effects, but nutritionally knowledgeable doctors advise that neither form of niacin be taken in large amounts without a nutritionally-oriented doctor's counsel. (4)

In addition, high doses of niacin can cause an acute attack in someone with porphyria, simply because niacin stimulates the production of heme. (5) The latter is produced by the pophyrin enzymes. Mutations or defects in the eight precursors of porphyrin enzymes cause the various inherited or acquired errors of metabolism in porphyria patients. Because heme can be produced in every cell, anything that triggers the production of heme to a larger extent can initiate a highly damaging, and often extremely painful, free-radical chain reaction that affects many organs and systems throughout the porphyria patient's body. (2) Not only the patient, but also all of his or her physicians need to know what to avoid, it is sometimes difficult and it can be impossible to avoid a porphyria attack, but every effort must be made; an acute hepatic porphyria attack may cause paralysis or can even kill the patient. (6,7)

The body responds differently to the various mutations. Different porphyrias (or mutations that lead to the tendency for porphyrins to accumulate throughout the body) need different treatments. It is essential that patients who may have porphyria receive the proper testing and interpretation of the tests, as well as the correct treatment, in as timely a manner as possible. (7) For more information please contact the American Porphyria Foundation, P.O. Box 22712, Houston, Texas 77227 USA. Their website is www.enterprise.net/apf. The website password <HOUSTON> ensures ready access for physicians.

Judy Kitchen

3637 Serra Road

Malibu, California 90265 USA

Phone/Fax 310-456-6837

References

(1.) Guengerich, Peter K, Influence of nutrients and other dietary materials on cytechrome P-450 enzymes, Department of Biochemistry and center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232-0146 or American Journal of Clinical Nutrition 1996; 61 (supplement) 651S-8S.

(2.) Wilson, cynthia, chemical Intolerance: Hallmark Feature of MCS and Porphyria, Our Toxic Times, chemical Injury Information Network, MT, October 1996.

(3.) Murray, Michael T., ND, Encyclopedia of Nutritional Supplements; Prima Publishing, CA 1996.

(4.) Lininger, Schuyler W., Jr., DC, Gaby, Alan R., MD, Austin, Steve, ND, Drown, Donald J., ND, Wright, Jonathan V., MD, Duncan, Alice, DC, CCH, The Natural Pharmacy, Prima Publishing 1099.

(5.) Wilson, Cynthia, Porphyrinogenic Substances, Chemical Injury Information Network, MT. 406-5472255.

(6.) Ridley, Alan, The Neuropathy of Acute Intermittent Porphyria, Quarterly Journal of Medicine News Series XXXVIII, No. 151, July 1969.

(7.) Porphyria News, American Porphyria Foundation, Texas, Spring 2003.

COPYRIGHT 2003 The Townsend Letter Group
COPYRIGHT 2003 Gale Group

Return to Porphyria
Home Contact Resources Exchange Links ebay