Test Catalog

Test Id : WGSEQ

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Gamma-Globin Full Gene Sequencing, Varies

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Overview

Test Catalog

Useful For
Suggests clinical disorders or settings where the test may be helpful

An adjunct in the interpretation of hemoglobin electrophoresis results

 

Evaluation for suspected gamma variants or nondeletional hereditary persistence of fetal hemoglobin

 

Assessment of unstable gamma chain variants when other tests for causes of hemolysis are unrevealing

Genetics Test Information
Provides information that may help with selection of the correct genetic test or proper submission of the test request

The beta-like hemoglobins include the epsilon, gamma, beta, and delta globins, whose genes are present on chromosome 11 in a linked cluster (ie, the beta globin complex). The gamma genes, HBG1 (Ay) and HBG2 (Gy), contain 3 exonic coding regions and 2 intronic intervening sequences (IVS). The genes produce gamma globin chains that form tetramers with alpha globin chains to create fetal hemoglobin (Hb F). HBG1 and HBG2 differ only in which amino acid is located at position 136 (alanine or glycine). The resultant proteins are named A-gamma and G-gamma, respectively. Although G-gamma is predominant at birth, this gradually reverses during the first year of life to become the normal adult G-gamma/A-gamma ratio, which is 2:3. Some people maintain an increased G-gamma:A-gamma ratio throughout life, which has been linked to certain alterations in either gene. Additionally, some alterations in the promoter regions of the gamma globin genes are known to cause a form of hereditary persistence of fetal hemoglobin (HPFH), which is characterized by a significant but harmless elevation of Hb F into adulthood. If coinherited with sickle cell disease, HPFH has a strong modulating effect on the condition and appears to protect against some, but not all, of its complications. Some gamma genetic variations result in gamma chain hemoglobin variants, most of which are clinically insignificant; however, an incompletely studied subset causes neonatal disorders, such as hemolytic anemia, cyanosis, and methemoglobinemia.

Highlights

This test should be used as an adjunct to abnormal results detected by hemoglobin electrophoresis testing. It will assist with:

-Diagnosis of nondeletional hereditary persistence of fetal hemoglobin (HPFH)

-Identification of abnormal gamma chain variants (eg, unstable, high- or low-oxygen affinity, or M hemoglobins)

-Predicting the severity of a coinherited sickling disorder

-Evaluation of unexplained neonatal anemia, cyanosis, or hyperbilirubinemia

Method Name
A short description of the method used to perform the test

Polymerase Chain Reaction (PCR) Amplification/Sanger Sequence Analysis

NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.

Yes

Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test

Gamma Globin Full Gene Sequencing

Aliases
Lists additional common names for a test, as an aid in searching

HBG1

HBG2

HBGA

HBGG

Gamma hemoglobin

Agamma

Ggamma

Hereditary persistence of fetal hemoglobin

Specimen Type
Describes the specimen type validated for testing

Varies

Necessary Information

A complete patient history is strongly encouraged.

Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing

Submit only 1 of the following specimens:

 

Specimen Type: Whole blood

Container/Tube:

Preferred: Lavender top (EDTA)

Acceptable: Yellow top (ACD)

Specimen Volume: 4 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send whole blood specimen in the original tube. Do not aliquot.

Specimen Stability Information: Refrigerate 30 days(preferred)/Ambient 14 days

 

Specimen Type: Extracted DNA from whole blood

Container/Tube: 1.5 to 2 mL tube

Specimen Volume: Entire specimen

Collection Instructions: Label specimen as extracted DNA from blood and provide indication of volume and concentration of the DNA

Specimen Stability Information: Frozen (preferred)/Refrigerate/Ambient

Special Instructions
Library of PDFs including pertinent information and forms related to the test

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:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Thalassemia/Hemoglobinopathy Patient Information (T358)

3. If not ordering electronically, complete, print, and send a Benign Hematology Test Request (T755) with the specimen.

Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.

Blood: 1 mL; Extracted DNA: 50 mcL at 50 ng/mcL concentration

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

Gross hemolysis OK
Bone marrow
Paraffin-embedded tissue
Frozen tissue
Paraffin-embedded bone marrow aspirate clot
Methanol-acetic acid (MAA)-fixed pellets
Moderately to severely clotted 		Reject

Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

Specimen Type Temperature Time Special Container
Varies Varies

Useful For
Suggests clinical disorders or settings where the test may be helpful

An adjunct in the interpretation of hemoglobin electrophoresis results

 

Evaluation for suspected gamma variants or nondeletional hereditary persistence of fetal hemoglobin

 

Assessment of unstable gamma chain variants when other tests for causes of hemolysis are unrevealing

Genetics Test Information
Provides information that may help with selection of the correct genetic test or proper submission of the test request

The beta-like hemoglobins include the epsilon, gamma, beta, and delta globins, whose genes are present on chromosome 11 in a linked cluster (ie, the beta globin complex). The gamma genes, HBG1 (Ay) and HBG2 (Gy), contain 3 exonic coding regions and 2 intronic intervening sequences (IVS). The genes produce gamma globin chains that form tetramers with alpha globin chains to create fetal hemoglobin (Hb F). HBG1 and HBG2 differ only in which amino acid is located at position 136 (alanine or glycine). The resultant proteins are named A-gamma and G-gamma, respectively. Although G-gamma is predominant at birth, this gradually reverses during the first year of life to become the normal adult G-gamma/A-gamma ratio, which is 2:3. Some people maintain an increased G-gamma:A-gamma ratio throughout life, which has been linked to certain alterations in either gene. Additionally, some alterations in the promoter regions of the gamma globin genes are known to cause a form of hereditary persistence of fetal hemoglobin (HPFH), which is characterized by a significant but harmless elevation of Hb F into adulthood. If coinherited with sickle cell disease, HPFH has a strong modulating effect on the condition and appears to protect against some, but not all, of its complications. Some gamma genetic variations result in gamma chain hemoglobin variants, most of which are clinically insignificant; however, an incompletely studied subset causes neonatal disorders, such as hemolytic anemia, cyanosis, and methemoglobinemia.

Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Hemoglobin F (HbF) is the dominant hemoglobin at birth but is gradually replaced by adult hemoglobin (HbA) during the year after birth (normal value < or =1% of total hemoglobin after age 2 years). Increased HbF levels may continue after the neonatal period and into adulthood for various reasons. Genetic causes include deletional and nondeletional forms of hereditary persistence of fetal hemoglobin (HPFH) and delta-beta thalassemia variants. Over 100 genetic variants have been described in the gamma genes and, if detectable, the protein expression will vary over time according to the overall HbF expression. Gamma globin variants can manifest either as a quantitative (gamma thalassemia or nondeletional HPFH) or a qualitative (gamma variant) abnormality. Nondeletional HPFH alterations frequently modulate the expected severity of sickling disorders due to the inhibitory properties of HbF on sickle formation. Many gamma chain variants are benign, although some, such as unstable, high- and low-oxygen affinity, or M hemoglobin variants, cause hemolytic anemia/hyperbilirubinemia, erythrocytosis, cyanosis, and methemoglobinemia, respectively. The percentages of gamma variants will vary according to if they are present on the HBG1 or HBG2 genes, as these genes are differentially expressed depending on the age of the patient. Symptoms due to gamma variants are expected to decrease along with the normal decrease in HbF and therefore, most resolve after the first 6 months of life.

Reference Values
Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Interpretation
Provides information to assist in interpretation of the test results

An interpretive report will be provided and will include specimen information, assay information, and whether the specimen was positive for any variants in the gene. If positive, the alteration will be correlated with clinical significance if known.

Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This test cannot be used in isolation to confirm or exclude hemoglobin conditions. Large deletions, crossover events, as well as other variants may not be detected. This test is used in conjunction with adequately studied protein analysis results.

 

If multiple alterations are identified, gamma globin gene sequencing is not able to distinguish between variants that are found in the same allele (in cis) and variants found on different alleles (in trans). This limitation of sequencing may complicate diagnosis or classification and has implications for inheritance and genetic counseling. To resolve these cases, molecular results must be correlated with electrophoretic and protein data and/or family studies.

Clinical Reference
Recommendations for in-depth reading of a clinical nature

1. Crowley MA, Mollan TL, Abdulmalik OY, et al. A hemoglobin variant associated with neonatal cyanosis and anemia. N Engl J Med. 2011;364(19):1837-1843

2. Cui J, Baysdorfer C, Azimi M, et al. Identification of three novel Hb F variants: Hb F-Hayward [(G)gamma1(NA1)Gly>Asp, GGT>GAT], Hb F-Chori-I [(A)gammaT16(A13)Gly>Asp, GGC>GAC] and Hb F-Chori-II [(A)gammaI29(B11)Gly>Glu, GGA>GAA]. Hemoglobin. 2012;36:305-309

3. Akinsheye I, Alsultan A, Solovieff N, et al. Fetal hemoglobin in sickle cell anemia. Blood. 2011;118(1):19-27

4. Steinberg M, Forget B, Higgs D, Weatherall D, eds. Disorders of Hemoglobin Genetics, Pathophysiology, and Clinical Management. 2nd ed. Cambridge University Press; 2009

5. Provan D, Gribben J, eds. Molecular Hematology. 3rd ed. Blackwell Publishing; 2010

6. Hoyer JD, Kroft SH, eds. Color Atlas of Hemoglobin Disorders: A Compendium Based on Proficiency Testing. College of American Pathologists; 2003

7. Merchant S, Oliveira JL, Hoyer JD, Viswanatha DS. Molecular diagnosis in hematopathology. In: Goldblum J. Hsi E, eds. Hematopathology: A Volume in the Series: Foundations in Diagnostic Pathology. 2nd ed. Churchill Livingstone; 2012:chap 24

8. Semkiu KM, Oliveira JL, Nguyen PL, Porter TR, Wilson DB. Hb F-Wentzville [(G)gamma24(B6)Gly>Glu; HBG2: c.74G>A, p.Gly25Glu]: An unstable (G)gamma-globin variant associated with neonatal hemolytic anemia. Hemoglobin. 2020;44(1):67-69. doi:10.1080/03630269.2020.1716002

Method Description
Describes how the test is performed and provides a method-specific reference

Total genomic DNA is extracted from the sample, and the full gamma globin genes are amplified by polymerase chain reaction in separate reactions followed by Sanger sequencing. Review of the sequence data is performed using a combination of automated calls and manual inspection.(Unpublished Mayo method)

PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information

No

Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday through Friday

Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

10 days

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

Blood: 2 weeks; DNA: 3 months

Performing Laboratory Location
Indicates the location of the laboratory that performs the test

Rochester

Fees :
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.

  • Authorized users can sign in to Test Prices for detailed fee information.
  • Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
  • Prospective clients should contact their account representative. For assistance, contact Customer Service.

Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.

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.

CPT Code Information
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.

CPT codes are provided by the performing laboratory.

81479-Unlisted molecular

LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.

Test Id Test Order Name Order LOINC Value
WGSEQ Gamma Globin Full Gene Sequencing 95795-1
Result Id Test Result Name Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
46952 Gamma Globin Gene Sequencing Result 50397-9
46953 Gamma Globin Interpretation 59466-3

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports