What is porphyria?
Porphyria is a term that refers to a group of disorders—the
porphyrias—that affect the nervous system or skin, or both. Each
type of porphyria is due to the deficiency of one of the enzymes
needed to make a substance in the body called heme. Enzymes are
proteins that help chemical reactions happen in the body. Making
heme involves a series of eight different enzymes, each acting in
turn.
Heme is a red pigment composed of iron linked to a chemical called
protoporphyrin. Heme has important functions in the body. The
largest amounts of heme are in the blood and bone marrow in the
form of hemoglobin within red blood cells. Hemoglobin gives blood
its red color and carries oxygen from the lungs to all parts of
the body. In the liver, heme is a component of proteins that have
many functions, including breaking down hormones, drugs, and other
chemicals and generating high-energy compounds that keep liver
cells alive and functioning normally.
The body makes heme mainly in the bone marrow and the liver. The
process of making heme is called the heme biosynthetic pathway.
Each step of the process is controlled by one of eight enzymes. If
any one of the enzymes is deficient, the process is disrupted. As
a result, porphyrin or its precursors chemicals formed at earlier
steps of the process may build up in body tissues and cause
illness.
What
are the types of porphyria?
The table below lists each type of porphyria and the deficient
enzyme responsible for the disorder. Porphyrias are often
classified as acute or cutaneous. Acute types of porphyria affect
the nervous system, whereas cutaneous types mainly affect the
skin. Two forms of porphyria hereditary coproporphyria and
variegate porphyria may be either acute or cutaneous, or both.
Type of Porphyria
Deficient Enzyme
Acute Porphyrias
ALAD porphyria
delta-aminolevulinic acid dehydratase
acute intermittent porphyria
porphobilinogen deaminase
hereditary coproporphyria
coproporphyrinogen oxidase
variegate porphyria
protoporphyrinogen oxidase
Cutaneous Porphyrias
congenital erythropoietic porphyria
uroporphyrinogen III cosynthase
porphyria cutanea tarda
uroporphyrinogen decarboxylase (~50% deficiency)
hepatoerythropoietic porphyria
uroporphyrinogen decarboxylase (~90% deficiency)
hereditary coproporphyria
coproporphyrinogen oxidase
variegate porphyria
protoporphyrinogen oxidase
erythropoietic protoporphyria
ferrochelatase
The most common type of
porphyria overall is porphyria cutanea tarda. In the United
States, acute intermittent porphyria is the most common acute
porphyria.
What causes porphyria?
Most porphyrias are inherited disorders, meaning they are caused
by abnormalities in genes passed from parents to children.
Scientists have identified the genes for all eight enzymes in the
heme pathway. Some forms of porphyria result from inheriting an
abnormal gene from one parent. Other forms are due to inheriting
two abnormal genes one from each parent. The risk that members of
an affected family will have the disease or transmit it to their
children depends on the type of porphyria.
One type of porphyria porphyria cutanea tarda is most often an
acquired disorder. It occurs when factors other than genes cause
an enzyme deficiency in the liver.
Porphyria can be triggered by
drugs such as barbiturates, tranquilizers, birth control pills,
and sedatives
chemicals
fasting
smoking
drinking alcohol, especially heavy drinking
infections
excess iron in the body
emotional and physical stress
menstrual hormones
exposure to the sun
What are the
symptoms of porphyria?
People with cutaneous forms of
porphyria develop blisters, itching, and swelling of their skin
when it is exposed to sunlight. Symptoms of acute forms of
porphyria include pain in the abdomen, chest, limbs, or back;
numbness, tingling, paralysis, or cramping; vomiting;
constipation; and personality changes or mental disorders. Acute
attacks of porphyria can develop over hours or days and last for
days or weeks.
Symptoms can vary widely in
severity. Some people with gene mutations that can cause porphyria
have no signs or symptoms of the disorder. These people are said
to have latent porphyria.
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