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Test ID: PPOXK    
PPOX Gene, Known Mutation

Useful For Suggests clinical disorders or settings where the test may be helpful

Predictive testing for variegate porphyria when a PPOX mutation has been identified in an affected family member

Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request

Documentation of the specific familial mutation must be provided with the specimen in order to perform this test.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Variegate porphyria (VP) is an autosomal dominant (AD) cutaneous porphyria that can present with/or without acute attacks that phenocopy acute intermittent porphyria (AIP). The most common clinical presentation of VP is increased photosensitivity, blistering, hyperpigmentation, and skin fragility in sun-exposed areas. The acute attacks of VP can include abdominal pain, vomiting, diarrhea, constipation, urinary retention, acute episodes of neuropathic symptoms, psychiatric symptoms, seizures, respiratory paralysis, tachycardia, and hypertension. Respiratory paralysis can progress to coma and death. Cutaneous manifestations include edema, sun-induced erythema, acute painful photodermatitis, and urticaria. In some cases patients present with isolated photosensitivity.

 

Variegate porphyria is caused by mutations in the PPOX gene. Mutations are typically inherited in an autosomal dominant fashion with incomplete penetrance, although homozygous mutations have been reported in association with a more severe clinical phenotype in early childhood.

 

Acute attacks may be prevented by avoiding both endogenous and exogenous triggers. These triggers include porphyrogenic drugs, hormonal contraceptives, fasting, alcohol, tobacco, and cannabis.

 

Fecal porphyrins analysis and quantitative urinary porphyrins analysis are helpful in distinguishing variegate porphyria from AIP and hereditary coproporhpyria.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Interpretation Provides information to assist in interpretation of the test results

An interpretive report will be provided.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

The identification of a disease-causing mutation in an affected family member is necessary before predictive testing for other family members can be offered. If a familial mutation has not been previously identified, order PPOXS / PPOX Gene, Full Gene Analysis.

 

Analysis is performed for the familial mutation provided only. This assay does not rule-out the presence of other mutations within this gene or within other genes that may be associated with porphyria.

 

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Any error in the diagnosis or in the pedigree provided to us, including false paternity, could lead to erroneous interpretation of results.

 

A previous bone marrow transplant from an allogenic donor will interfere with testing. Call Mayo Medical Laboratories for instructions for testing patients who have received a bone marrow transplant.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Siegesmund M, van Tuyll van Serooskerken AM, Poblete-Gutierrez P, Frank J: The acute hepatic porphyrias: current status and future challenges. Best Pract Res Clin Gastroenterol 2010 Oct;24(5):593-605

2. Anderson KE, Bloomer JR, Bonkovsky HL, et al: Recommendations for the diagnosis and treatment of the acute porphyrias. Ann Intern Med 2005 Mar 15;142(6):439-450

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test