Porphyria testing: PPOX, CPOX, UROD, HMBS, FECH

Diagnostic Use

Note that (aside from cascade family screening) genotyping is NOT the front line test for porphyria.
Urine PBG is the single most important test to exclude acute porphyria.
Investigation for porphyria requires a full set of samples - blood, urine and faeces protected from the light.

Genotyping for any of the porphyria types should only be considered after good clinical and biochemical phenotyping. It should be possible to target the single most likely affected gene.

If a mutation is identified in a case, cascade family screening of first degree family members should be considered after appropriate counselling and should be focused on the genetic variant that has been identified.

The porphyrias are a group of low penetrance, autosomal dominant disorders which generally present with excessive accumulation and excretion of protoporphyrin. The symptoms are variable but include: severe abdominal pain, chest, legs or back pain, constipation or diarrhea, nausea and vomiting, muscle pain, tingling, numbness, weakness or paralysis, red or brown urine, mental changes, such as anxiety, confusion, hallucinations, disorientation or paranoia, breathing problems, urination problems, heart palpitations, hypertension, seizures.

Approximately 75% of affected individuals remain asymptomatic but are at risk if exposed to certain drugs, alcohol or other factors.

Department

Genetics - Molecular Pathology

Delphic Registration Code

MOLP

Constituent Tests

• Genomic DNA Extraction

Turnaround Time

4 weeks

Test Code

7312

Specimen Type

• Whole Blood

Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

4.0

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

1.0

Minimum Sample Volume (ml)

0.5

Pre-testing Requirements

Biochemical investigations should be performed before genetic porphyria analysis is requested.

Additional Specimen Information

This test requires nucleated cells. Please do not centrifuge or freeze the blood samples.
If storing blood tube prior to delivery please refrigerate at 4 degrees (transport still at ambient temperature).

Aliquot Instructions

Sample Type

• Whole Blood

Transport to Lab

Ambient (8 - 24 degrees Celsius)

Additional Referral/Aliquot Information

Please do not centrifuge or freeze the blood samples.
If storing blood tube prior to delivery please refrigerate at 4 degrees (transport still at ambient temperature).

Interpretation

Genotyping for any of the porphyria types should be guided by good clinical and biochemical phenotyping. It should be possible to identify the single most likely affected gene.

Where a mutation is identified, many of the porphyrias have low penetrance and may not necessarily manifest clinically. Avoidance of porphyrinogenic drugs or other agents may be appropriate.

Where a mutation is identified, cascade family screening of close family members should be considered after genetic counselling.

Test Method

Coding regions of the 5 most common genes implicated in the hereditary porphyrias are analysed by DNA sequencing: PPOX, CPOX, UROD, HMBS, FECH.

The decision as to which genes are analysed will be guided by the clinical biochemistry results (e.g. fecal porphyrins, appropriate plasma fluorescent peaks) and the requesting physician.

The precise cost of porphyria gene testing depends on the number of exons in the genes that are analysed.

Non-Funded Test Cost

$1980.66 (Exclusive of GST)

Billing Code

4584

Additional Costing Information

The precise cost of porphyria gene testing depends on the number of exons in the genes that are analysed.

Genomic DNA must be extracted from the specimen prior to testing. This incurs an additional charge (see GDNA). Laboratories may prefer to submit DNA for testing. Please provide a minimum of 5 micrograms of DNA at 20 nanograms/microlitre.

Contact Information

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