Test ID: FECHS
Ferrochelatase (FECH) Gene, Full Gene Analysis

Confirmation of a diagnosis of erythropoietic protoporphyria (EPP) following positive biochemical genetic test results obtained through PEE/88886 Porphyrins Evaluation, Whole Blood

Carrier testing for individuals with a family history of EPP in the absence of known mutations in the family

• Molecular Genetics-Biochemical Disorders Patient Information Sheet
• Informed Consent for Genetic Testing

Polymerase Chain Reaction (PCR) Followed by DNA Sequence Analysis
(PCR is utilized pursuant to a license agreement with Roche Molecular Systems, Inc)

Forms:

1. Molecular Genetics-Biochemical Disorders Patient Information Sheet (Supply T527) in Special Instructions

2. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.

3. If not ordering electronically, submit a Molecular Genetics Request Form (Supply T245) with the specimen.

Specimen must arrive within 96 hours of collection.

Submit only 1 of the following specimens:

Preferred:

Blood

Container/Tube: Lavender top (EDTA) or yellow top (ACD)

Specimen Volume: 3 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send specimen in original tube.

Specimen Stability Information: Ambient (preferred)/Refrigerated

Acceptable:

Blood Spots

Container/Tube: Whatman Protein Saver 903 Paper

Specimen Volume: 5 blood spots

Collection Instructions:

1. Let blood dry on the filter paper at ambient temperature in a horizontal position for 3 hours.

2. Do not expose specimen to heat or direct sunlight.

3. Do not stack wet specimens.

4. Keep specimen dry.

Specimen Stability Information: Ambient (preferred)/Refrigerated

No specimen should be rejected. If specimen is not received at the appropriate temperature or in the wrong anticoagulant, include note to laboratory. If questions, contact laboratory.

Erythropoietic protoporphyria (EPP) is an inherited disorder of porphyrin metabolism whose clinical manifestations include painful photodermatosis without blisters and liver disease. The disorder results from decreased activity of the enzyme ferrochelatase (FECH). FECH is the last of 8 enzymes acting sequentially in the heme biosynthetic pathway and is encoded by the FECH gene located on chromosome 18.

The skin symptoms in EPP include immediate painful photosensitivity, usually beginning in early infancy upon sun exposure. Repeated photosensitivity episodes result in skin thickening and areas of hyperkeratosis. This is typically noted on areas where sun exposure is most common, such as the dorsa of the hands and on the face. A small number of patients with EPP develop liver complications. Hepatic disease in EPP may include cholelithiasis and chronic liver disease progressing to rapid acute liver failure.

Biochemically, EPP is characterized by elevated protoporphyrin levels in red blood cells, which fluorescence under Wood’s light due to the accumulation of free protoporphyrin IX. Protoporphyrin elevations may also be found in plasma and stool, but not in all patients. Urine protoporphyrin levels are usually normal unless there is liver involvement. Studies have also suggested that a reduction in activity of ferrochelatase to <50% of normal levels can induce clinical manifestations. The gold standard test for the diagnosis of EPP is biochemical analysis (#88886 Porphyrins Evaluation, Whole Blood), interpreted in the context of clinical features.

In most patients with EPP, a pathogenic FECH mutation that reduces enzyme activity by 50% can be identified on only 1 allele. Clinical expression of EPP typically requires a hypomorphic (low expression) FECH allele (IVS3-48T->C) in trans (on a different chromosome) with the mutation. IVS3-48T->C is a variant of the FECH gene associated with reduced gene expression. This variant is found in approximately 10% of the general Caucasian population. Autosomal recessive inheritance (2 pathogenic mutations in trans) is infrequent, accounting for <4% of EPP cases. In contrast to patients with 1 pathogenic mutation and the low-expression allele, missense mutations are far more common than null mutations.

It is uncertain whether protoporphyric liver failure is more common among individuals with a single null (splicing defect, nonsense, or frameshift) mutation than those with 2 pathogenic mutations as some literature has suggested. In any case, it is certain that all EPP patients should be monitored for hepatic disease and actively manage their photosensitivity.

An interpretive report will be provided.

An interpretive report will be provided.

A small percentage of individuals who are carriers or have a diagnosis of erythropoietic protoporphyria (EPP) disease may have mutations that are not identified by this method (eg, large genomic deletions, promoter mutations). The absence of a mutation(s), therefore, does not eliminate the possibility of positive carrier status or the diagnosis of EPP disease. For carrier testing, it is important to first document the presence of a ferrochelatase (FECH) gene mutation in an affected family member.

This test does not exclude the presence of mutations within other genes, such as ALAS2 (aminolevulinate, delta-, synthase 2), that are associated with EPP, X-linked or otherwise.

In some cases, DNA alterations of undetermined significance may be identified.

Rare polymorphisms exist that could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, additional testing should be considered.

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. 

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in our interpretation of results may occur if information given is inaccurate or incomplete.

1. Lecha M, Puy H, Deybach JC: Erythropoietic protoporphyria. Orphanet J Rare Dis 2009;4:19

2. Schneider-Yin X, Gouya L, Meier-Weinand A, et al: New insights into the pathogenesis of erythropoietic protoporphyria and their impact on patient care. Eur J Pediatr 2000;159:719-725

3. Rufenacht UB, Gouya L, Schneider-Yin X, et al: Systematic analysis of molecular defects in the ferrochelatase gene from patients with erythropoietic protoporphyria. Am J Hum Genet 1998;62:1341-1352

4. Whatley SD, Mason NG, Holme SA, et al: Molecular epidemiology of erythropoietic protoporphyria in the U.K.. Br J Dermatol 2010;162:642-646

Fluorescent DNA sequence analysis is used to test for the presence of mutations in all 11 coding exons of the ferrochelatase (FECH) gene. GenBank accession number; NM_ 000140.3. (Unpublished Mayo method)

Tuesday, 10am

81479-Unlisted molecular pathology procedure