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!]


King George III should have sued
From Science News, 8/6/05 by Nathan Seppa

The madness of King George III of England might have been the fault of his doctors as much as of substandard royal genes. An analysis of preserved locks of the king's hair shows that his body harbored high amounts of arsenic, which could have exacerbated his inherited neurological problems.

George III, who reigned from 1760 to 1820, had bouts of madness that sometimes lasted months. Scientists have proposed that the sovereign was periodically deranged by an inherited disease called porphyria, which has cropped up occasionally since then in European royalty. The disease stems from defects of metabolism that cause toxic chemicals to accumulate, damaging the nervous system.

Absorption of certain metals by the body can obstruct some of these same metabolic processes.

In an effort to determine whether such obstruction was a factor in the king's mental health, researchers at the University of Kent in England looked for lead or other metals in samples of George's hair stored at the Science Museum in London. In the July 23 Lancet, they report finding an arsenic concentration of 17 parts per million (ppm). Normally, the concentration in hair is less than 1 ppm.

Royal records show that George's physicians frequently administered emetic tartar, a potion that contained antimony. Arsenic and antimony often coexist in nature. Given the doses of emetic tartar the king was getting, the researchers estimate that he could have been ingesting between 4 and 9 milligrams of arsenic per day. The records indicate that the treatments were sometimes administered against George's will.

"The [arsenic doses] are very high, but not high enough to cause acute poisoning," says study coauthor Martin J. Warren. However, he says, since arsenic affects the same metabolic pathway as porphyria, "arsenic may have precipitated his [porphyria] attacks or made them much more severe."

COPYRIGHT 2005 Science Service, Inc.
COPYRIGHT 2005 Gale Group

Return to Porphyria
Home Contact Resources Exchange Links ebay