Test Id : G6PDZ

For cord blood specimens that have an accompanying maternal blood specimen, maternal cell contamination studies will be performed at an additional charge.

The following are available:

-Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency Diagnostic Algorithm

-Glucose-6-Phosphate Dehydrogenase (G6PD) Genotyping Interpretive Algorithm

For initial or time-sensitive screening for glucose-6-phosphate dehydrogenase deficiency, order G6PD1 / Glucose 6-Phosphate Dehydrogenase Enzyme Activity, Blood.

Patient Preparation: A previous hematopoietic stem cell transplant from an allogenic donor will interfere with testing. For information about testing patients who have received a hematopoietic stem cell transplant, call 800-533-1710.

Submit only 1 of the following specimens:

Specimen Type: Whole 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 whole blood specimen in original tube. Do not aliquot.

Specimen Stability Information: Ambient (preferred) 4 days/Refrigerated 4 days/Frozen 4 days

Additional Information:

1. Specimens are preferred to be received within 4 days of collection. Extraction will be attempted for specimens received after 4 days, and DNA yield will be evaluated to determine if testing may proceed.

2. To ensure minimum volume and concentration of DNA is met, the requested volume must be submitted. Testing may be canceled if DNA requirements are inadequate.

Specimen Type: Cord 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 cord blood specimen in original tube. Do not aliquot.

Specimen Stability Information: Ambient (preferred) 4 days/Refrigerated 4 days/Frozen 4 days

Additional Information:

1. Specimens are preferred to be received within 4 days of collection. Extraction will be attempted for specimens received after 4 days, and DNA yield will be evaluated to determine if testing may proceed.

2. To ensure minimum volume and concentration of DNA is met, the requested volume must be submitted. Testing may be canceled if DNA requirements are inadequate.

3. While a properly collected cord blood sample may not be at risk for maternal cell contamination, unanticipated complications may occur during collection. Therefore, maternal cell contamination studies are recommended to ensure the test results reflect that of the patient tested and are available at an additional charge. Order MATCC / Maternal Cell Contamination, Molecular Analysis, Varies on the maternal specimen.

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 (preferred) 30 days/Refrigerated 30 days

Additional Information: Saliva specimens are acceptable but not recommended. Due to lower quantity/quality of DNA yielded from saliva, some aspects of the test may not perform as well as DNA extracted from a whole blood sample. When applicable, specific gene regions that were unable to be interrogated will be noted in the report. Alternatively, additional specimen may be required to complete testing.

Specimen Type: Extracted DNA

Container/Tube:

Preferred: Screw Cap Micro Tube, 2mL with skirted conical base

Acceptable: Matrix tube, 1mL

Collection Instructions:

1. The preferred volume is at least 100 mcL at a concentration of 75 ng/mcL.

2. Include concentration and volume on tube.

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

Additional Information: DNA must be extracted in a CLIA-certified laboratory or equivalent and must be extracted from a specimen type listed as acceptable for this test (including applicable anticoagulants). Our laboratory has experience with Chemagic, Puregene, Autopure, MagnaPure, and EZ1 extraction platforms and cannot guarantee that all extraction methods are compatible with this test. If testing fails, one repeat will be attempted, and if unsuccessful, the test will be reported as failed and a charge will be applied. If applicable, specific gene regions that were unable to be interrogated due to DNA quality will be noted in the report.

• Informed Consent for Genetic Testing
• Pharmacogenomic Association Tables
• Glucose-6-Phosphate Dehydrogenase (G6PD) Genotyping Interpretive Algorithm
• Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency Diagnostic Algorithm

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:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing (Spanish) (T826)

2. If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

-Therapeutics Test Request (T831)

-Benign Hematology Test Request Form (T755)

See Specimen Required

Genetic test for individuals at high risk for glucose-6-phosphate dehydrogenase (G6PD) deficiency

Aiding in the diagnosis of G6PD deficiency

Determining G6PD deficiency status in individuals with inconclusive or unexpected phenotyping results

Differentiation of heterozygotes with skewed X-inactivation from homozygotes and compound heterozygotes

Definitive diagnosis of carrier status

Evaluation of neonates with unexplained jaundice

Identifying individuals at risk of drug-induced acute hemolytic anemia related to G6PD deficiency

This test is for molecular sequencing of the G6PD gene and does not assess glucose-6-phosphate dehydrogenase (G6PD) enzyme activity. Enzymatic testing may be suggested as follow-up to this assay. For G6PD enzyme testing order G6PD1 / Glucose 6-Phosphate Dehydrogenase Enzyme Activity, Blood.

G6PD deficiency is a common X-linked condition, estimated to affect up to 500 million people worldwide. Both male and female patients may be impacted due to how common G6PD deficiency is in the population.

Acute hemolytic anemia (AHA) can be triggered in individuals with G6PD deficiency by fava beans, several types of medications (including rasburicase, dapsone-containing combinations of antimalarial drugs, and methylene blue), and infection. Less commonly, chronic congenital nonspherocytic hemolytic anemia (CNSHA) may occur in severe forms of G6PD deficiency.

US Food and Drug Administration labeling and Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines recommend that G6PD testing be undertaken in high-risk populations before prescribing drugs known to cause AHA. Knowing a patient's genotype is generally sufficient to avoid contraindicated drugs, but follow-up with the phenotyping (enzyme) assay may be necessary to clarify results in some cases.

This test involves full gene sequencing of all exons and exon/intron boundaries of the G6PD gene. A comprehensive interpretation will be provided including congenital and pharmacogenomic implications of results. Testing should be considered before prescribing medication associated with hemolysis in individuals with G6PD deficiency.

For cord blood specimens that have an accompanying maternal blood specimen, maternal cell contamination studies will be performed at an additional charge.

The following are available:

-Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency Diagnostic Algorithm

-Glucose-6-Phosphate Dehydrogenase (G6PD) Genotyping Interpretive Algorithm

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzymopathy, estimated to affect up to 500 million people worldwide. It is most frequently found in populations where Plasmodium falciparum malaria is (or was) endemic, but G6PD deficiency may be present in any population.(1)

Glucose-6-phosphate dehydrogenase deficiency primarily manifests as episodic acute hemolytic anemia (AHA), chronic non-spherocytic hemolytic anemia (CNSHA), and neonatal jaundice. These clinical manifestations can be triggered in individuals with G6PD deficiency by fava beans, several types of medications (including rasburicase, dapsone-containing combinations of antimalarial drugs, and methylene blue), and infection.(1,2)

Glucose-6-phosphate dehydrogenase converts glucose-6-phosphate to 6-phosphoglyconolactone in the first step of the pentose phosphate pathway, this reaction also produces nicotinamide adenine dinucleotide phosphate (NADPH) from NADP(+). NADPH, through subsequent enzymatic reactions, protects erythrocytes from damage by detoxifying hydrogen peroxide and other sources of oxidative stress. (3)

Glucose-6-phosphate dehydrogenase is encoded by the gene G6PD, which lies on the X-chromosome. G6PD deficiency is inherited in an X-linked recessive manner; therefore, male patients are more commonly affected than female patients, but due to the high prevalence of G6PD deficiency, homozygous and compound heterozygous female patients are not uncommon. Over 200 G6PD variants have been discovered and are classified based on guidance from the World Health Organization (WHO). In 2022, WHO proposed updated guidance for the classification of G6PD variants (Table).(4) This revised guidance is based on the median residual enzyme activity and seeks to resolve problems identified with the WHO G6PD classification system that has been in place since 1985 (Table).(4)

Table. Updated and Legacy G6PD Variant WHO Classification and Associated G6PD Deficiency Phenotype

With the exception of those with CNSHA, individuals with G6PD deficiency are typically asymptomatic until they are challenged with an exogenous factor, such as a drug, infection, or fava beans.(1) The exogenous factor can trigger AHA in individuals with G6PD deficiency. The severity of AHA is highly variable, ranging from mild neonatal jaundice to life-threatening complications, such as kernicterus.(1) Therefore, determining the G6PD deficiency status is recommended on the US Food and Drug Administration label of several drugs either proven or suspected to cause AHA in patients with G6PD deficiency. For more information on drugs known to cause AHA in individuals with G6PD deficiency, see Pharmacogenomic Associations Tables. In addition, the Clinical Pharmacogenetics Implementation Consortium has published a guideline related to medication use in the context of G6PD genotype.(5)

Preemptive genotyping allows for the identification of patients at risk for an adverse reaction to drugs known to cause AHA in those with G6PD deficiency. In most cases, genotyping provides sufficient information to avoid the use of contraindicated drugs. In some cases, including heterozygous female patients, the phenotyping assay is necessary to determine if such drugs should be avoided. Skewed X-inactivation in heterozygous female patients has been reported to result in G6PD deficiency, so the phenotyping assay is necessary to determine G6PD activity level.(3)

An interpretive report will be provided.

All detected alterations will be evaluated according to the latest American College of Medical Genetics and Genomics recommendations and the most recent World Health Organization system for classifying genetic variants of G6PD.(1,2) Variants will be classified based on known, predicted, or possible effect on gene pathogenicity and reported with interpretive comments detailing their potential or known significance.

Patients who have received a non-leukocyte reduced blood transfusion within the preceding 6 weeks can have inaccurate genetic test results due to the presence of both donor and recipient DNA. For patients who have been transfused within the preceding 6 weeks, the glucose-6-phosphate dehydrogenase (G6PD) enzyme assay will also be affected, so it is not an appropriate alternative test. Patients who have received an allogeneic hematopoietic stem cell transplant would be expected to convert to the G6PD status of the donor; therefore, it is appropriate to perform G6PD sequencing on a whole blood sample. However, if the patient's transplant is not fully engrafted (chimerism is present) or if there is a relapse of an underlying hematologic malignancy, a mixture of donor and recipient genotype may be seen on genetic analysis. The enzyme assay can be run after transplantation; order G6PD1 / Glucose 6-Phosphate Dehydrogenase Enzyme Activity, Blood.

Rare variants exist that could lead to false-negative or false-positive results. Other variants in the primer binding regions can affect the testing, and ultimately, the genotype assessment made.

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Large deletions or rearrangements are not detected by this assay.

Sometimes a genetic variant of uncertain significance may be identified. In this case, testing of appropriate family members, as well as testing enzyme activity, may be useful to determine pathogenicity of the alteration.

This test is not designed to provide specific dosing or drug selection recommendations and is to be used as an aid to clinical decision making only. Drug-label guidance should be used when dosing patients with medications regardless of the predicted phenotype.

Skewed X-inactivation in heterozygous female patients has been reported to result in G6PD deficiency. In these cases, the phenotyping (enzyme) assay is necessary to determine G6PD activity level and assign G6PD deficiency status.

Rarely, incidental or secondary findings may implicate another predisposition or presence of active disease. Incidental findings may include, but are not limited to, results related to the sex chromosomes. These findings will be carefully reviewed to determine whether they will be reported.

1.Luzzatto L, Ally M, Notaro R. Glucose-6-phosphate dehydrogenase deficiency. Blood. 2020;136(11):1225-1240. doi:10.1182/blood.2019000944

2.Luzzatto L, Seneca E. G6PD deficiency: a classic example of pharmacogenetics with on-going clinical implications. Br J Haematol. 2014;164(4):469-480

3.Cappellini MD, Fiorelli G. Glucose-6-phosphate dehydrogenase deficiency. Lancet. 2008;371(9604):64-74

4.Global Malaria Programme, Malaria Policy Advisory Group. Meeting report of the technical consultation to review the classification of glucose-6-phosphate dehydrogenase (G6PD). World Health Organization; 2022. Accessed July 3, 2023. Available at www.who.int/publications/m/item/WHO-UCN-GMP-MPAG-2022.01

5. Gammal RS, Pirohamed M, Somogyi AA, et al. Expanded clinical pharmacogenetics implementation consortium guideline for medication use in the context of G6PD genotype. Clin Pharmacol Ther. 2023;113(5):973-985.

6.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;17(5):105-423

Genomic DNA is extracted from whole blood. The G6PD gene is amplified by polymerase chain reaction (PCR). The PCR products are then purified and sequenced in both directions using fluorescent dye-terminator chemistry. Sequencing products are separated on an automated sequencer and trace files analyzed for variations in the exons and intron/exon boundaries of all exons using variant detection software and visual inspection. Variant nomenclature is based on GenBank accession number NM_001042351.2 using human genome assembly GRCh37 (hg19).(Unpublished Mayo method)

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

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