HBB Deletion/Duplication Analysis

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Test Details

Use

HBB deletion/duplication analysis is intended for individuals who have a clinical diagnosis of β-thalassemia and have either one or no pathogenic variants detected by HBB full gene sequencing. This test may also be used for carrier screening in individuals at increased risk of being an HBB carrier but have tested negative by HBB full gene sequencing. If testing is needed for a known familial large deletion or duplication, please submit a copy of the laboratory report documenting the familial variant in the index family member.

Limitations

Multiplex ligation-dependent probe amplification (MLPA) is designed to detect single exon, multi-exon, and full gene deletions or duplications. MLPA may not detect certain genomic rearrangements, such as translocations, inversions, mosaic variants, or some partial exon rearrangements. This assay cannot determine exact breakpoints of deletions or duplications detected. Diagnostic errors may occur due to rare sequence variations.

This test was developed, and its performance characteristics determined, by LabCorp. It has not been cleared or approved by the US Food and Drug Administration (FDA).

Methodology

Multiplex ligation-dependent probe amplification (MLPA)

Additional Information

β-Thalassemia is a typically autosomal-recessive form of severe anemia. Prevalence is estimated at 1:100,000 worldwide and at 1:10,000 in the European Union, reflecting the increased prevalence in Mediterranean populations. Based on disease severity, three types of β-thalassemia are distinguished: β-thalassemia major (also known as Cooley's anemia), β-thalassemia intermedia, and β-thalassemia minor (also known as β-thalassemia trait). β-Thalassemia minor is mostly asymptomatic, but may be accompanied by mild anemia. In contrast, β-thalassemia major is characterized by infancy-onset severe anemia and requires life-long blood transfusions for survival. By definition, the intermediate form requires only intermittent blood transfusions for survival. Bone marrow or cord blood transplantation offers a cure, especially if performed before lasting organ damage has developed. Early diagnosis is, therefore, crucial to allow timely treatment initiation. Distinction between the intermediate and major forms is also important to avoid both unnecessary transfusions and unnecessary delay of required regular transfusions, which can increase the risk that the patient may develop multiple antibodies against donor red blood cells. Genetic testing can help with this diagnosis, since severity of β-thalassemia can partially be predicted from the nature of the causative mutations in HBB, the gene coding for β-globin. In addition, genetic testing can also identify mutations associated with rare cases of dominantly inherited β-thalassemia. Once the mutations causing β-thalassemia in a specific family have been identified, genetic testing for these mutations can also help to diagnose affected siblings of patients prenatally or directly after birth and facilitate genetic counseling in other relatives.

Specimen Requirements

Specimen

Whole blood or amniotic fluid or chorionic villus sample (CVS)

Volume

7 mL whole blood or 10 mL amniotic fluid or 10 mg CVS

Container

Lavender top (EDTA) or yellow-top (ACD) or sterile plastic conical tube or two confluent T-25 flasks for fetal testing

Storage Instructions

Maintain specimen at room temperature.

Causes for Rejection

Frozen specimen; hemolysis; quantity not sufficient for analysis; improper container; HBB sequencing not previously performed

Clinical Information

Special Instructions

Full HBB gene sequencing is required (β-Thalassemia: HBB (Full Gene Sequencing) [252823]) before deletion/duplication analysis can be performed. If testing is needed for a known familial large deletion or duplication, please submit a copy of the laboratory report documenting the familial variant in the index family member.

References

Cao A, Galanello R. Beta-Thalassemia. GeneReviews. 2010. Available at: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=b-thal. Accessed August 1, 2010. 20301599
Galanello R, Origa R. Beta-thalassemia. Orphanet J Rare Dis. 2010 May 21; 5:11. 20492708
Thein SL. Genetic modifiers of beta-thalassemia. Haematologica. 2005 May; 90(5):649-660. 15921380

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
252240 HBB Deletion/Duplication 252241 Extraction 8100-0
252240 HBB Deletion/Duplication 252268 Test Order Review N/A
Reflex Table for Test Order Review
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 252274 HBB Deletion/Duplication 252271 Specimen Type 31208-2
Reflex Table for Test Order Review
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 252274 HBB Deletion/Duplication 252272 Result 21689-5
Reflex Table for Test Order Review
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 252274 HBB Deletion/Duplication 252273 Director Review 72486-4
Reflex Table for Test Order Review
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 252274 HBB Deletion/Duplication 511936 PDF 80563-0

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The LOINC® codes are copyright © 1994-2017, Regenstrief Institute, Inc. and the Logical Observation Identifiers Names and Codes (LOINC) Committee. Permission is granted in perpetuity, without payment of license fees or royalties, to use, copy, or distribute the LOINC® codes for any commercial or non-commercial purpose, subject to the terms under the license agreement found at https://loinc.org/license/. Additional information regarding LOINC® codes can be found at LOINC.org, including the LOINC Manual, which can be downloaded at LOINC.org/downloads/files/LOINCManual.pdf