VP is a deficiency of the enzyme protoporphyrinogen oxidase, due to a mutation, or change, in the PPOX gene in the heme biosynthesis pathway. The disorder is autosomal dominant. The enzyme deficiency alone is not sufficient to produce the symptoms of VP and other activating factors, such as drugs, hormones, and dietary changes, must be present. Sometimes activating factors cannot be identified. Most people who have a mutation in the gene for VP never develop symptoms; this is referred to as “latent” VP. Symptoms may develop after puberty, especially in women. Unlike AIP, symptoms may also include photosensitivity.
Acute attacks almost always start with severe pain in the abdomen but sometimes in the chest, back, or thighs, and are often accompanied by nausea, vomiting, and constipation. Heart rate and blood pressure are commonly increased. These symptoms and signs are all due to the effects of the disease on the nervous system. Confusion, convulsions, and muscular weakness due to impairment of the nerves controlling the muscles may lead to paralysis. An acute attack usually lasts for days or weeks. Recovery from severe paralysis is generally slow.
DNA analysis of the PPOX gene is performed by full gene sequencing of all exons (coding regions), 20-30 base pairs into the introns (including splice sites), and the promoter region. This methodology should identify >99% of mutations listed in the Human Gene Mutation Database as well as novel mutations.
Targeted mutation analysis, looking for the specific family's PPOX mutation, can also be performed. Documentation of the family's mutation must be provided.
Prenatal diagnosis is also available. Prior to ordering prenatal testing, please contact our laboratory at 212-241-7518 to discuss.
- Full DNA analysis: 20 ml of whole blood in EDTA (anticoagulant) tubes (lavender top) OR extracted DNA (50μl with concentration of 200ng/μl).
- Targeted mutation analysis: 20ml of whole blood in EDTA (anticoagulant) tubes (lavender top) OR extracted DNA (30μl with concentration of 200ng/μl) OR buccal cells (buccal brushes MUST be requested from laboratory).
Prenatal: Testing requires prior documentation of parental mutation.
- Chorionic Villi: 5-10 mg in conical tube with sterile saline OR transport media
- Amniotic Fluid: 10 ml in conical tube
- Cultured cells: two confluent T-25 flasks
Additionally, please send:
- 5-10 ml maternal blood in EDTA (lavender top) required to perform MCC studies on all prenatal samples and in case maternal confirmation studies are necessary
- 5-10 ml paternal blood in EDTA (lavender top) in case paternal confirmation studies are necessary
Shipping: Ship at room temperature.
Post-natal: 10-14 days
Prenatal: 3-5 days
Full gene sequencing: 81406, 81479, G0452
Targeted mutation analysis: 81403, 81479, G0452
Consent Form: Porphyria Genetic Testing Consent [PDF]
Requisition Form: Porphyria Testing Requisition [PDF]
Related Tests: Acute Porphyrias Panel (AIP, HCP & VP)