Porphyria Educational Services
PORPHYRIA EDUCATIONAL SERVICES BULLETIN
Vol. 2 No. 20 May 14, 2000
FOCUS: HEREDITARY COPROPORPHYRIA [HCP]
In the hepatic acute porphyrias there are three main types, with
the most prevalent being AIP. There are also two similar acute
porphyrias which have cutaneous manifestations in addition to the
neurological manifestions, these being VP and HCP.
In this bulletin we will explore HCP, which is a relative
newcomer to the acute hepatic porphyrias. Isolated just a little
over a decade ago, HCP is now well known. It is very similar to
VP in many resoects.
HCP is an autosomal dominant disorder resulting from a deficiency
of coproporphyrinogen oxidase.
Hereditary coproporphyria (HCP) is similar to acute intermittent
porphyria, although it is less common as aforementioned. It i is
often milder, and occasionally is associated with
photosensitivity. A few homozygous
cases have been identified.
Similar to other porphyrias, HCP is genetically heterogeneous at
the level of the coproporphyrinogen oxidase gene . This enzyme
catalyzes the two-step decarboxylation of coproporphyrinogen III
to protoporphyrinogen IX. An intermediate product is a
tricarboxyl porphyrinogen termed harderoporphyrinogen.
In a biochemical variant of HCP, called harderoporphyria, a
mutation causes a structural alteration in the enzyme that
reduces substrate affinity, and harderoporphyrin as well as
coproporphyrin accumulates.
Symptomology of HCP demonstrate in acute attacks of abdominal and
neurologic symptoms. These symptoms are precipitated by the same
factors that are important in acute intermittent porphyria,
including certain drugs (eg, barbiturates, sulfonamides) and
steroids (especially progesterone) as well as other chemical
toxins.
In HCP photosensitivity sometimes occurs but less commonly than
in variegate porphyria.
The diagnosis of HCP is based on finding increased amounts of ALA,
PBG, and coproporphyrin in urine and excess coproporphyrin in
feces. [A predominant or exclusive presence of fecal
coproporphyrin is more suggestive of HCP than of variegate
porphyria, in which fecal coproporphyrin and protoporphyrin
concentrations are usually about equal.]
Urinary ALA, PBG, and uroporphyrin may be increased during acute
attacks. These normalize between attacks more commonly than in
acute intermittent porphyria.
Coproporphyrinogen oxidase deficiency can be demonstrated in
cells other than erythrocytes, but this is not recommended for
routine diagnosis.
The reatment of HCP acute attacks is the same as that for acute
intermittent porphyria.