Hereditary coproporphyria

Hereditary coproporphyria (HCP) is a form of hepatic porphyria associated with a deficiency of the enzyme coproporphyrinogen III oxidase.

Hereditary coproporphyria (HCP) is an autosomal recessive genetic disease that causes purple urine, photosensitivity, and attacks of abdominal pain. Symptoms vary from mild to severe and can be regulated with diet and triggered with drug use.

Symptoms
Symptoms include reddish-purple urine, acute neurological problems (typically episodic confusion and sensory changes), and attacks of acute abdominal/nerve pain. Around 30% suffer photosensitive skin eruptions with nail involvement; these can lead to permanent scarring.

Triggers vary, but infections, hormonal changes, dieting, and the use of alcohol and certain drugs such as barbiturates and birth control pills have all been implicated.

Function
The coproporphinogen oxidase gene is an enzyme expressed in erythrocytes that converts coproporphyrinogen III to protoporphyrinogen IX. Heme is made from porphyrin and when a mutation occurs, heme production is interrupted. This leads to an overabundance of porphyrin in the body, which then exits through urine/feces.

Pathophysiology
Hereditary coproporphyria is the result of a point mutation in the coproporphinogen oxidase (CPO) gene. Documented changes in the DNA sequence that cause HCP include missense, nonsense, deletion and splicing of single nucleotides. Documented changes in the protein sequence have been a replacement of ser208 to phe(s208f) and arg328 to cys(r328c). Aside from varying intensity of symptoms there are no other known mutations, and it is not known at this time if mutations in other genes can trigger this same disease. At this time it is not known if there are any specific groups of people that are especially susceptible to this disease, as patients have been documented all over the world.

Molecular Biology
The CPO gene is located in chromosome 3 on the q12 locus. The gene is 14,000 bases in length, has 6 introns, and 7 exons. Once the introns are spliced out the actual coded mRNA is only 2675 bases in length. The protein contains 323 amino acids.

Heredity
HCP is an autosomal disease, meaning it is carried in one of the autosomes, or non-sex chromosomes. There have been documented cases of both heterozygous and homozygous inheritance, with similar symptoms in each patient.

Treatment
While there is no cure for this condition, there are preventative measures people can take to regulate symptoms. A diet high in carbohydrates, as well as avoidance of aggravating factors (such as alcohol and drug use) can prevent attacks.