VP is a deficiency of the enzyme protoporphyrinogen oxidase, due to a mutation, or change, in the PPOX gene. 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 HCP never develop symptoms; this is referred to as “latent” HCP. 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.
Two 10 mL EDTA (lavendar top) tubes and one 10 mL ACD (yellow top) tube. Two to three confluent T-25 flasks of cultured cells and one control flask are required for prenatal samples.
Shipping: Send at room temperature.
Turnaround Time: 14 days
CPT Codes: 83891, 83898x4, 83904x8, 83912
Consent Form: Porphyria Genetic Testing Consent [PDF]
Requisition Form: Porphyria Genetic Testing Consent [PDF]
Related Tests: Acute Porphyrias Panel (AIP, HCP & VP)
Prior to ordering prenatal testing, please contact our laboratory at 212-241-7518 to discuss.