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Test ID: HMBSZ HMBS Gene, Full Gene Analysis

Useful For

Confirming a diagnosis of hydroxymethylbilane synthase deficiency/acute intermittent porphyria

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
CULFB Fibroblast Culture for Genetic Test Yes No

Testing Algorithm

If skin biopsy is received, fibroblast culture will be added and charged separately.

Method Name

Polymerase Chain Reaction (PCR) Amplification/DNA Sequencing

Reporting Name

HMBS Gene, Full Gene Analysis

Specimen Type

Varies


Specimen Required


Specimen preferred to arrive within 96 hours of collection.

 

Submit only 1 of the following specimens:

 

Preferred:

Specimen Type: Whole blood

Container/Tube:

Preferred: Lavender top (EDTA) or yellow top (ACD)

Acceptable: Any anticoagulant

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

 

Specimen Type: Cultured fibroblasts

Container/Tube: T-75 or T-25 flask

Specimen Volume: 1 Full T-75 or 2 full T-25 flasks

Specimen Stability Information: Ambient (preferred)/Refrigerated <24 hours

 

Specimen Type: Skin biopsy

Container/Tube: Sterile container with any standard cell culture media (eg, minimal essential media, RPMI 1640). The solution should be supplemented with 1% penicillin and streptomycin. Tubes can be supplied upon request (Eagle's minimum essential medium with 1% penicillin and streptomycin [T115]).

Specimen Volume: 4-mm punch

Specimen Stability Information: Refrigerated (preferred)/Ambient

 

Acceptable:

Specimen Type: Blood spot

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


Specimen Minimum Volume

Blood: 1 mL/Blood Spots: 3

Specimen Stability Information

Specimen Type Temperature Time
Varies Varies

Clinical Information

Hydroxymethylbilane synthase (HMBS) deficiency is an autosomal dominant disorder with incomplete penetrance that can present as acute intermittent porphyria (AIP). The most common clinical presentation of AIP is abdominal pain. Acute attacks can include 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. HMBS deficiency can also be without clinical or biochemical manifestations.

 

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

 

The measurement of porphobilinogen deaminase (PBG-D) enzyme activity in erythrocytes facilitates detection of AIP during latent periods, and also confirms a biochemical diagnosis during acute episodes. However, a normal result does not completely exclude a diagnosis of HMBS deficiency/AIP. The preferred diagnostic test is molecular genetic testing of the HMBS gene.

Reference Values

An interpretive report will be provided.

Interpretation

All detected alterations are evaluated according to American College of Medical Genetics recommendations.(1) Variants are classified based on known, predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or known significance.

Clinical Reference

1. Richards S, Aziz N, Bale S, et al: Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Genet Med 2015 May;17(5):405-424

2. Thunell S: Hydroxymethylbilane Synthase Deficiency. In GeneReviews. Edited by RA Pagon, TD Bird, CR Dolan, K Stephens. University of Washington, Seattle. 1993-2005 Sep27 (updated 2011 Sep 01)

3. 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

4. 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

Day(s) and Time(s) Performed

Performed weekly, Varies

Analytic Time

14 days

CPT Code Information

81479-Unlisted molecular pathology procedure

 

Fibroblast Culture for Genetic Test

88233-Tissue culture, skin or solid tissue biopsy (if appropriate)

88240-Cryopreservation (if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
HMBSZ HMBS Gene, Full Gene Analysis In Process

 

Result ID Test Result Name Result LOINC Value
52443 Result Summary 50397-9
52444 Result In Process
52445 Interpretation In Process
52446 Additional Information 48767-8
52447 Specimen 31208-2
52448 Source 31208-2
52449 Released By No LOINC Needed

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

Forms

1. Molecular Genetics: Biochemical Disorders Patient Information (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 (T576) is available in Special Instructions.

Mayo Medical Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

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