Thursday, April 11, 2019

What is Variegate Porphyria (VP)?

What is Variegate Porphyria (VP)?

VP is an inherited genetic condition with similar clinical signs and symptoms as AIP, but  is more rare than AIP. VP is especially common in South African individuals of Dutch ancestry, where it has been estimated that 3 in 1,000 of the Caucasian population is affected. In VP, the gene responsible is PPOX which produces the enzyme coproporphyinogen oxidase, and without this enzyme working properly porphyrins build up and can cause symptoms similar to those seen in AIP. However the acute attacks can be milder in people with VP when compared to AIP. Patients with VP have the same slightly increased risk of liver cancer that AIP patients have. Unlike AIP, people with VP can also have blistering on their skin in response to sun exposure and the primary affected areas are on the back of the hands and face. The occurrence of blistering skin lesions are much more common in VP than in HCP and are not easily treated. The only effective preventive measure is use of protective clothing and avoidance of prolonged sun exposure. As in AIP, about 80-90% of patients with VP mutations will not develop symptoms.

How is Variegate Porphyria diagnosed?

There are two types of testing; biochemical, meaning looking for “biomarkers” in the blood or urine, and genetic, meaning looking at the gene we know causes the disease directly from a blood sample.
Biochemical: To diagnose VP, measurement of porphobilinogen (PBG), aminolevulinic acid (ALA), and total porphyrins in the urine should be done. Also porphyrins in the blood should be measured. The level of PBG in the body can vary so the best time to take samples is during an acute attack (e.g. when someone is having abdominal pain, etc.). Slight elevations in porphyrins are not diagnostic of VP; the levels need to be very high.
Genetic: A blood sample is used to look at a person’s genes and by doing this it is possible to see if their genes have changes that can cause disease, called mutations. VP is caused by mutations in the PPOX gene. Genetic testing is recommended for patients even if they have a biochemical diagnosis of VP.
If a patient has a mutation, their immediate family members should be tested for that same mutation as well.  This includes their parents, their siblings, and any children they may have. This will allow all family members to receive appropriate care and counseling even though 80-90% of people with a mutation will not have symptoms of VP.

What are treatments for Variegate Porphyria?

The treatments and preventive measures are the same as in AIP. In addition patients with blistering from sun exposure will need to protect themselves from sunlight by using sun protective clothing and avoiding prolonged sun exposure.

How is Variegate Porphyria Inherited?

VP is an autosomal dominant condition. Autosomal means that the defect is not on the chromosomes that determine sex, and dominant means that you only need to inherit one mutated gene to manifest the disease. The gene that causes HCP is called PPOX.
Genes are inherited randomly, so a parent has an equal chance of passing on either copies of each gene. Since most VP patients have one mutated copy and one normal copy, this means that each of their children will have a 50% chance of inheriting the mutated copy and 50% chance of inheriting the working copy.

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