What else is it called?
- Porphyria variegate
- Porphyria, South African type
- Protoporphyrinogen oxidase deficiency
- PPOX deficiency
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What causes it?
VP is caused by mutations (changes) in the PPOX gene. This gene is responsible for making an enzyme called protoporphyrinogen oxidase. Mutations in the PPOX gene reduce the activity of that enzyme which allows a compound called porphyrin precursors to build up in the body.
These compounds are formed during normal production of heme protein, but reduced activity of protoporphyrinogen oxidase allows them to build up to toxic levels.
The acute attacks associated with this condition can be brought on by several different factors including certain medication, hormonal changes in the body, alcohol, dieting and other factors that have not been identified.
How common is it?
The condition is estimated to occur in 1 in 100,000 individuals in European populations. The disorder is most prevalent in South Africa in individuals of Dutch ancestry. This is due to a founder effect which is when a small isolated population of settlers expands over several generations and causes a high prevalence of a genetic trait.
Most individuals with VP in South Africa carry the same PPOX mutation and are ancestors of a Dutch settler from the late 1600s. The prevalence of VP in South Africa amongst Caucasians is estimated to be 1 to 3 in 1,000 individuals.
What are the signs and symptoms?
Symptoms of VP can vary from patient to patient. The most common symptoms are skin symptoms and neurological symptoms or both. Symptoms usually start in adulthood.
Skin symptoms are linked to sun sensitivity and individuals with VP may develop:
- Discoloration after sun exposure
Neurological symptoms are related to acute attacks. These attacks may occur after taking certain medications, hormonal changes, dieting or alcohol. For some individuals with VP the exact cause for an attack may be unknown. During an attack of VP symptoms include:
- Abdominal pain
- Muscle weakness
- Increased heart rate
- Increased blood pressure
Attacks can vary in length from a few days to weeks. Most symptoms go away quickly after an attack however, some symptoms such as muscle weakness can take months to get better.
Hepatocellular carcinoma (type of cancer that starts in the liver) has been reported as a rare complication of VP.
Individuals with VP are also at risk to develop kidney disease.
How is it diagnosed?
A diagnosis of VP starts with different tests including urine, stool and blood tests. The diagnosis is made by finding an excess of the compounds, coproporphyrin in the urine and both coproporphyrin and protoporphyrin in the stool.
Genetic testing of the PPOX gene can be used to confirm the diagnosis.
Can it be treated?
Hospitalization is often necessary to help manage the pain and other neurological symptoms during acute attacks. Medications are also given for pain nausea and vomiting, and close observation is necessary. Mild attacks can be managed by giving the patient large amounts of glucose of other carbohydrates. Please not that any dietary changes require a specialist dieticians’ advice and monitoring. More severe attacks can be treated with hemin which is an injection of the heme protein and will help stop the attack.
The prognosis for individuals with VP can vary based on the severity of symptoms. With early diagnosis and proper treatment, the condition is rarely life threatening and is unlikely to get worse with time. That being said, people with VP are at an increased risk for liver cancer and kidney disease.
Do my family need to be tested?
VP is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of VP is autosomal dominant. This means that one copy of the altered gene in each cell is enough to cause the disorder. A person affected by an autosomal dominant disorder such as VP has a 50% chance of passing the mutated gene to each child. There is also a 50% chance that the child will not inherit the mutated gene.
Genetic counselling can be requested to get a full explanation.