OTHER FORMS OF PORPHYRIA
The most commonly encountered porphyrias
are acute
intermittent porphyria (AIP),
porphyria
cutanea tarda (PCT), erythropoietic
protoporphyria (EPP) and
variegate
porphyria. Each of these
is described in detail on its own
pages.
 The
remaining porphyrias are much more
rarely encountered and are briefly
summarised here. As with all porphyrias,
they result from enzyme
defects in the haem
synthetic pathway as illustrated
on the right.
HEREDITARY COPROPORPHYRIA
This is an autosomal
dominant condition. In simple terms, this means
that only one parent need be affected for the children
to run the risk of showing the disease. In fact, each
child will have a 50% chance of inheriting that disease.
Both boys and girls stand an equal chance of inheriting
the disease.
Patients may develop photosensitivity
with typical skin disease and are also at risk of the
acute
attack. They must therefore observe drug
precautions.
The disease arises from a mutation
in the gene
for the enzyme
coproporphyrinogen oxidase.
This deficiency results in a characteristic
accumulation of coproporphyrin,
particularly in the stool, which
may be tested in making the diagnosis.
CONGENITAL ERYTHROPOIETIC
PORPHYRIA (CEP)
This is an autosomal
recessive condition. Both parents need to carry
a mutation
in the gene
for the enzyme
uroporphyrinogen cosynthase in order for the
disease to manifest. CEP is extremely rare. It presents
with skin disease, which is often severe and accompanied
by photomutilation.
In CEP, haem
synthesis within the bone marrow is affected,
and this may lead to some relatively minor abnormalities
in the blood including anaemia, haemolysis (breakdown
of red blood cells) and a slightly enlarged spleen.
It is diagnosed by showing an abnormal
accumulation of porphyrins
in the red blood cells and urine.
ALA DEHYDRATASE
(DOSS) PORPHYRIA
This excessively rare porphyria is
associated with acute attacks only. Skin disease is
not a feature. It is an autosomal
recessive condition. Both parents need to carry
a mutation
in the gene
for the enzyme
ALA dehydratase in order for the disease to manifest.
It is diagnosed by showing very high
levels of ALA
with a low or normal PBG
level in the urine.
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