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Test ID: 2B6Q Cytochrome P450 2B6 Genotype, Varies


Ordering Guidance


Testing is available as the single gene assay (this test) and as a part of a psychotropic pharmacogenomics panel.

 

If genotype testing for psychotropic medications is desired, order PSYQP / Psychotropic Pharmacogenomics Gene Panel, Varies.



Specimen Required


Submit only 1 of the following specimens:

 

Specimen Type: Whole blood

Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send specimen in original tube.

Specimen Stability Information: Ambient (preferred) 9 days/Refrigerated 30 days

 

Specimen Type: Saliva

Patient Preparation: Patient should not eat, drink, smoke, or chew gum 30 minutes prior to collection.

Supplies: Saliva Swab Collection Kit (T786)

Specimen Volume: 1 Swab

Collection Instructions: Collect and send specimen per kit instructions.

Specimen Stability Information: Ambient 30 days

 

Specimen Type: Extracted DNA

Container/Tube: 2 mL screw top tube

Specimen Volume: 100 mcL (microliters)

Collection Instructions:

1. The preferred volume is 100 mcL at a concentration of 50 ng/mcL.

2. Include concentration and volume on tube.

Specimen Stability Information: Frozen (preferred) 1 year/Ambient/Refrigerated


Forms

1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available in Special Instructions:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.

Useful For

Aiding in determining therapeutic strategies for drugs that are metabolized by cytochrome P450 (CYP) 2B6

 

Providing information relevant to bupropion, efavirenz, ketamine, methadone, and nevirapine, as well as other medications metabolized by CYP2B6

 

Determining the genotype if genotype-phenotype discord is encountered clinically after testing with a less comprehensive genotyping method has occurred

 

Identifying genotype when required for drug trials and research protocols

Method Name

Real Time-Polymerase Chain Reaction (RT-PCR) with Allelic Discrimination Analysis

Reporting Name

CYP2B6 Genotype, V

Specimen Type

Varies

Specimen Minimum Volume

Blood: 1 mL
Saliva: 1 swab

Specimen Stability Information

Specimen Type Temperature Time Special Container
Varies Varies

Clinical Information

The cytochrome P450 (CYP) family of enzymes is a group of oxidative/dealkylating enzymes localized in the microsomes of many tissues including the intestines and liver. CYP2B6 is wholly or partially responsible for the metabolism of several commonly prescribed drugs.

 

The CYP2B6 gene is highly variable with over 38 named alleles. The gene can have multiple sequence variations. Alleles thought to have an impact upon CYP2B6 enzyme function at the time that this test was developed are included in this test (See Table 1). Individuals without a detectable gene alteration will be reported as CYP2B6*1/*1, but it is possible that these individuals harbor unknown variants that may impact metabolism. In addition, some individuals have genes that are hybrids of CYP2B6 and the CYP2B7 pseudogene. The frequency of these hybrids is unknown, and this assay does not test for these hybrids.

 

Phenotyping is derived from the Pharmacogene Variation Consortium website(1), an exhaustive review of the CYP2B6 literature, the Clinical Pharmacogenetics Implementation Consortium website(2), and published guidelines.(3) CYP2B6 genotype results are used to predict metabolizer phenotypes. A CYP2B6 phenotype is predicted based upon the number of functional, partially functional, and nonfunctional alleles present in a sample. In rare instances where alleles with unknown function are present in a homozygous or compound heterozygous state, an unknown phenotype occurs. It should be noted that other laboratories may use different phenotype prediction methods as there is no consensus on this at this time. However, the method used here represents the findings of the majority of literature available.

 

Several medications act as substrates of CYP2B6. CYP2B6-metabolized medications with the highest quality of data for the impact of various CYP2B6 alleles on metabolism are:

-Bupropion

-Efavirenz

-Ketamine

-Methadone

-Nevirapine

 

Other enzymes may be involved in the metabolism of these drugs. For example, bupropion is also metabolized by CYP2D6. Efavirenz is also metabolized by CYP2A6, although CYP2B6 is the major metabolizing enzyme. Ketamine is also metabolized by CYP2A6, and nevirapine is also metabolized by CYP3A4 and CYP3A5. CYP2A6 testing is not available clinically at the time this document was written, but CYP2D6 (2D6Q / Cytochrome P450 2D6 Comprehensive Cascade, Varies), CYP3A4 (3A4Q / Cytochrome P450 3A4 Genotype, Varies), and CYP3A5 (3A5Q / Cytochrome P450 CYP3A5 Genotype, Varies) testing is available.

 

There is a variable degree of substrate specificity exhibited by CYP2B6 alleles on these medications. This means that the same allele (ie, *6) may not metabolize all substrates at exactly the same rate.

 

Drugs that are metabolized by CYP2B6 may require dosage adjustment based on the individual patient's genotype. For example, patients who are poor metabolizers may require much lower than usual doses to achieve optimal response in the case of drugs that are inactivated by the CYP2B6 enzyme. Alternatively, patients who are ultrarapid metabolizers may benefit from increased doses in the case of drugs that are inactivated by CYP2B6 enzyme. In the absence of clear guidance from the FDA on dosing for various metabolizer phenotypes, patients with either ultrarapid or poor metabolism may benefit by switching to comparable alternate medications that are not primarily metabolized by CYP2B6 or by therapeutic drug monitoring where applicable.

 

Table 1. Enzyme Activity of Individual Star Alleles

Enzyme activity

Examples of CYP2B6 star alleles

Normal (extensive) activity

*1, *5

Increased activity

*4, *22

Decreased activity

*6, *7, *9, *11, *14, *15, *19, *20, *26, *27, *36

No or null activity

*8, *12, *13, *16 (also known as *18.002), *18, *35, *38

Unknown activity

 *27

Reference Values

An interpretive report will be provided.

Interpretation

An interpretive report will be provided.

 

The genotype, with associated star alleles, is assigned using standard allelic nomenclature as published by the Pharmacogene Variation (PharmVar) Consortium.(1)

 

For additional information regarding pharmacogenomic genes and their associated drugs, see Pharmacogenomic Associations Tables in Special Instructions. This resource also includes information regarding enzyme inhibitors and inducers, as well as potential alternate drug choices.

Clinical Reference

1. PharmVar. Pharmacogene Variation Consortium. Updated March 3, 2021. Accessed March 22, 2021. Available at www.pharmvar.org/

2. Clinical Pharmacogenetics Implementation Consortium (CPIC). Accessed October 14, 2020. Available at https://cpicpgx.org/

3. Desta Z, Gammal RS, Gong L, et al: Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2B6 and Efavirenz-Containing Antiretroviral Therapy. Clin Pharmacol Ther. 2019;106(4):726-733. doi: 10.1002/cpt.1477

4. U.S National Library of Medicine: DailyMed. National Institutes of Health.. Accessed October 14, 2020. Available at https://dailymed.nlm.nih.gov/dailymed/index.cfm

Day(s) Performed

Monday through Friday

Report Available

3 to 8 days

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 US Food and Drug Administration.

CPT Code Information

81479

LOINC Code Information

Test ID Test Order Name Order LOINC Value
2B6Q CYP2B6 Genotype, V 72511-9

 

Result ID Test Result Name Result LOINC Value
610082 CYP2B6 Genotype 72882-4
610083 CYP2B6 Phenotype 79720-9
610566 CYP2B6 Activity Score In Process
610084 Interpretation 69047-9
610085 Additional Information 48767-8
610086 Method 85069-3
610087 Disclaimer 62364-5
610088 Reviewed by 18771-6
Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

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