Hereditary Coproporphyria (HCP)
This is an autosomal dominant form of hepatic Porphyria that is similar to AIP, except that some patients develop skin photosensitivity. The deficient enzyme is coproporphyrinogen oxidase. The diagnosis is established by finding excess coproporphyrin (especially coproporphyrin type III) in urine and stool. High urine coproporphyrin is nonspecific and can be due to many things, such as liver disease. Therefore, by itself, high coproporphyrins do not mean that a patient has HCP. When HCP causes high urine coproporphyrin, the stool coproporphyrin are also very high. Thus, the diagnosis of HCP is not established with coproporphyrins unless stool porphyrins (mostly coproporphrin lll) are measured and are high as well. DNA studies can also be done, keeping in mind that rarely with any porphyria, including HCP, a mutation can’t be found. ALA and PBG in the urine will be elevated. Other types of porphyrins show little or no increase. Urinary ALA and PBG are increased during acute attacks but may become normal on recovery. Reliable assays for the deficient enzyme are not generally available. If the enzyme is measured, red blood cells should not be used. The enzyme is found in mitochondria which are not present in red blood cells. Precautions and treatment for acute attacks are as described for AIP.
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