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Porphyria Educational Services

Vol. 2 No. 20 May 14, 2000

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.