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Gamma Globin (HBG1 and HBG2) Sequencing
3001957
Ordering Recommendation

Assess for gamma globin gene variants resulting in neonatal hemolytic anemia, cyanosis or methemoglobinemia in symptomatic infants when other etiologies have been excluded. Assess for nondeletional hereditary persistence of fetal hemoglobin (HPFH) in individuals with elevated fetal hemoglobin. Characterize abnormal hemoglobins identified by electrophoresis suspected to represent gamma chain variants.

Mnemonic
HBG FGS
Methodology
Polymerase Chain Reaction/Sequencing
Performed
Varies
Reported
Within 2 weeks
New York DOH Approval Status
Specimens from New York clients will be sent out to a New York DOH approved laboratory, if possible.
ARUP Consult®
Disease Topics
Specimen Required
Patient Preparation
 
Collect
Lavender (K2EDTA), Pink (K2EDTA), or Yellow (ACD Solution A or B). 
Specimen Preparation
Transport 3 mL whole blood. (Min: 1 mL) 
Storage/Transport Temperature
Refrigerated. 
Unacceptable Conditions
 
Remarks
 
Stability
Ambient: 1 week; Refrigerated: 1 month; Frozen: 6 months 
Reference Interval
By report
Interpretive Data
Background information for Gamma Globin (HBG1 and HBG2) Sequencing:
Characteristics:
Variants in the gamma globin genes, HBG1 and HBG2, may occasionally result in either a quantitative defect (gamma thalassemia or nondeletional hereditary persistence of fetal hemoglobin) or a qualitative abnormality (gamma variant). Gamma variants resulting in unstable, high- and low-oxygen affinity or M hemoglobin variants may result in hemolytic anemia/hyperbilirubinemia, erythrocytosis/cyanosis, or methemoglobinemia in neonates, respectively. Clinical symptoms related to gamma globin variants commonly resolve after the first six months of life given the switch from fetal hemoglobin expression to adult hemoglobin expression.
Incidence: Unknown.
Inheritance: Autosomal dominant.
Cause: Pathogenic germline variants in HBG1 or HBG2.
Clinical Sensitivity: Unknown. Gamma globin variants are a rare cause of neonatal hemolytic anemia, cyanosis, erythrocytosis, or methemoglobinemia.
Methodology: Long range PCR followed by nested PCR and bidirectional sequencing of all coding regions, intron/exon boundaries, proximal promoters, and 5' and 3' untranslated regions of the HBG1 and HBG2 genes.
Analytical Sensitivity and Specificity: 99 percent.
Limitations: Diagnostic errors can occur due to rare sequence variations or repeat element insertions. Large deletions/duplications, distal regulatory region variants, deep intronic variants, and hybrid gene events will not be detected.

Compliance Statement C: For human genetic inheritable conditions and mutations. This test was developed and its performance characteristics determined by ARUP Laboratories. The U. S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.

Counseling and informed consent are recommended for genetic testing. Consent forms are available online.

Note
Hotline History
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Components
Component Test Code*Component Chart NameLOINC
3002038Specimen HBG FGS
3002039HBG FGS Interpretation
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Aliases