Table of Contents
Porphyria – The collective term for a group of eight inherited GENETIC DISORDERS of METABOLISM in which deficiencies of certain enzymes block the production of heme and allow the accumulation of porphyrins. Heme is an iron-containing pigment normally present in nearly all tissues in the body, notably as a component of HEMOGLOBIN in the BLOOD and of electron transport proteins called cytochromes.
The LIVER produces cytochromes, which are essential for metabolizing numerous drugs, hormones, NUTRIENTS, and other substances. Heme synthesis occurs in a sequence of eight steps, each occurring through the actions of a particular enzyme. Each of the eight forms of porphyria represents the absence of one of these enzymes.
Symptoms of Porphyria and Diagnostic Path
Symptoms vary with the type and may be neurologic (affect the NERVOUS SYSTEM), dermatologic (affect the SKIN), hepatic (involve the liver), or erythropoietic (involve the BONE MARROW and blood). Typically symptoms are episodic, occurring as attacks that last for days to weeks and sometimes longer. Symptoms vary widely in appearance, severity, and duration and may include
- eruptive skin rashes (bullae)
- severe ABDOMINAL PAIN
- NAUSEA, VOMITING, and DIARRHEA
- MUSCLE weakness and possibly PARALYSIS
- agitation and hallucinations
- tachycardia (rapid HEART RATE)
- URINARY RETENTION and URINARY INCONTINENCE
The diagnostic path includes blood and urine tests to measure the presence of key porphyric enzymes. In people who know they have porphyria, exposure to identified precipitating factors —which include numerous drugs, hormones, and nutrients—will bring on an attack. HYPERTENSION (high BLOOD PRESSURE) can develop during an attack and persist after symptoms subside.
|Porphyria||Deficient Enzyme||Inheritance Pattern|
|acute intermittent porphyria (AIP)||porphobilinogen deaminase (PBG-D)||autosomal dominant|
|ALAD-deficiency porphyria (ADP)||aminolevulinic acid dehydratase (ALAD)||autosomal recessive|
|congenital erythropoietic porphyria (CEP)||uroporphyrinogen III cosynthase||autosomal recessive|
|erythropoietic protoporphyria (EPP)||ferrochelatase||autosomal dominant|
|hepatoerythropoietic porphyria (HEP)||uroporphyrinogen decarboxylase||autosomal recessive|
|hereditary coproporphyria (HCP)||coproporphyrinogen oxidase||autosomal dominant|
|porphyria cutanea tarda (PCT)||uroporphyrinogen decarboxylase||autosomal dominant|
|variegate porphyria (VP)||protoporphyrinogen oxidase||autosomal dominant|
Porphyria Treatment Options and Outlook
Severe symptoms, particularly neurologic, require hospitalization and aggressive treatment that may include intravenous heme administration (the only form in which heme is available). Medications safe to take to relieve and control symptoms include narcotic pain relievers and phenothiazines to relieve nausea and vomiting or neuropsychiatric symptoms. It is crucial to stop any substances that may have precipitated the attack. Most symptoms subside within two to three weeks, and most people fully recover within six weeks. Some people experience extended muscle weakness. Attacks may occur without provocation. Many people who have porphyria seldom experience attacks, however.
Risk Factors and Preventive Measures
The porphyrias are inherited genetic disorders. The risk of porphyria depends on the inheritance pattern. There are no measures to prevent porphyria. People who have porphyria, or who have family members who have porphyria, might consider GENETIC TESTING and GENETIC COUNSELING. It is possible to be a CARRIER for the autosomal recessive forms of porphyria.