Beta Thalassemia (HBB Sequence Analysis)
- Synonyms: Beta globin gene sequence analysis
- LIS Mnemonic: MBBTHAL
Collect
Collect whole blood in a purple top (EDTA) tube.
Volume Required
5 mls
Minimum Required
3 mls
Transport
Refrigerate sample until shipment. Send the sample at room temperature with overnight delivery for receipt Monday through Friday within 24 hours of collection.
Stability
Whole blood can be refrigerated until shipment.
Unacceptable conditions
Heparinized specimens, severely hemolyzed specimens, frozen, clotted or possibly commingled specimens, blood in non-sterile or leaky containers, mislabeled or inappropriately labeled specimens.
Specimen Handling
Do not heat, freeze or centrifuge blood before shipment. Refrigerate sample until shipment.
Days Performed
Mon - Fri 9:00am to 4:00pm
Reported
2-3 weeks
CPT
81404
Disease Information
Clinical Features:
Beta thalassemia is characterized by severe anemia, growth retardation, splenomegaly, bone changes with characteristic facies and iron depositions affecting cardiac and endocrine systems. Beta thalassemia is characterized by hypochromic, hemolytic anemia and dependence on blood transfusions to sustain life. Even with chelation therapy to remove excess iron stores, the life expectancy in classic beta thalassemia major is shortened to 25-30 years on average.
It has been estimated that 3% of the world’s population carries a beta thalassemia gene. These carriers, individuals with beta thalassemia trait, are essentially normal, although they can be detected by lowered mean corpuscular volume (MCV) typically <80fl, lowered mean corpuscular hemoglobin value (MCH) typically <26-34 pg/rbc and an elevated A2 level, typically 4.5-6.0. Determination of these values as well as ethnicity are very useful in diagnosis and should be obtained whenever possible.
Molecular Genetics:
The HBB gene is located on chromosome 11p15.5. The inheritance pattern is autosomal recessive. Beta thalassemia is caused by decreased or absent ß-globin chain production. The sickle cell mutations are found at codon 7 (HbS and HbC) while beta thalassemia mutations are found throughout the gene.
Test Methods:
We offer DNA sequence analysis and deletion testing of the entire coding region. Beta thalassemia and sickle cell (HbS) mutations are detected by sequencing the beta globin coding region and part of the intervening sequences. Sequence variants are classified as mutations, variants of unknown significance or benign variants unrelated to disease. Variants of unknown significance may warrant further studies in the patient and other family members.
Detection Rate:
Beta Thalassemia: Point mutations in the HBB gene are detected in 95-98% of patients with beta thalassemia. The analytical sensitivity is ~99%.
Sickle Cell: This assay will detect over 100% of HbS and HbC alleles. The analytical sensitivity is close to 100%.
Related Tests:
Known mutation analysis is available to family members for mutations previously identified by sequence analysis.
Prenatal testing is available to couples who are confirmed carriers of mutations. Please contact the laboratory director to discuss appropriate testing prior to collecting a prenatal specimen.
Results:
Test results with interpretation will be mailed and/or faxed to the referring physician or send out lab following completion of the test. Additional reports will be provided as requested.
Utility:
The clinical utility of the assay is to confirm a diagnosis of beta thalassemia, sickle/beta thal, or sickle cell disease; identify carriers of beta thal trait or sickle cell trait to facilitate prenatal testing and counseling for reproductive risk; prenatal analysis for beta thalassemia major or sickle cell disease; and to distinguish between beta thalassemia trait and other forms of anemia (ie, iron deficiency).
Remarks
Whole blood in EDTA purple top tubes is the preferred sample. High molecular weight genomic DNA, cheek epithelial cells, or other samples containing DNA may be acceptable. Contact the laboratory for specific instructions regarding such samples before sending the sample.
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- (215) 590-8736
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