Alpha Thalassemia Panel
Summary and Pricing
Test Method
Bi-Directional Sanger Sequencing and Multiplex Ligation-Dependent Probe Amplification AssayTest Code | Test Copy Genes | Panel CPT Code | Gene CPT Codes Copy CPT Code | Base Price | |
---|---|---|---|---|---|
6090 | HBA1 and HBA2 | 81479 | 81259,81269 | $1470 | Order Options and Pricing |
An additional 25% charge will be applied to STAT orders. STAT orders are prioritized throughout the testing process.
Turnaround Time
The great majority of MLPA assays are completed within 4 weeks. The great majority of reflexive Sanger sequencing are completed within an additional 4 weeks.
Please note: Once the testing process begins, an Estimated Report Date (ERD) range will be displayed in the portal. This is the most accurate prediction of when your report will be complete and may differ from the average TAT published on our website. About 85% of our tests will be reported within or before the ERD range. We will notify you of significant delays or holds which will impact the ERD. Learn more about turnaround times here.
Targeted Testing
For ordering sequencing of targeted known variants, go to our Targeted Variants page.
Clinical Features and Genetics
Clinical Features
Hemoglobin A, the main form of hemoglobin, is a polypeptide comprised of two alpha and two beta chains. Alpha chains are encoded through the HBA1 and HBA2 genes. Defects in these genes result in alpha thalassemia, which is a common hemoglobin disorder commonly found in African and Asian populations. Carrier frequencies are >1% due to a selective advantage of malaria resistance in these individuals. There are four clinical conditions ranging in severity from asymptomatic to hydrops fetalis: silent carrier, alpha thalassemia trait, hemoglobin H (HbH), and hemoglobin Bart hydrops fetalis (Hb Bart). Disease severity is correlated to the degree of impaired alpha chain production (Origa and Moi. 2016. PubMed ID: 20301608; Harteveld and Higgs. 2010. PubMed ID: 20507641).
The two main clinical forms of alpha thalassemia are Hb Bart and HbH. Hb Bart syndrome is a neonatal lethal disease characterized by pleural and pericardial effusions, severe hypochromic anemia, ascites, and generalized edema. HbH disease, also referred to as alpha thalassemia intermedia, is characterized by microcytic hypochromic anemia, splenomegaly, jaundice, and in some cases skeletal changes primarily affecting facial features. Onset for HbH ranges from first years of life to adulthood. HbH individuals may also develop gallstones, have iron overload, or acute hemolytic episodes during infections or in response to oxidant drugs. In more severe forms HbH individuals may require blood transfusions. Patients with alpha thalassemia trait may have mild anemia, but are largely symptomatic (Origa and moi. 2016. PubMed ID: 20301608; Harteveld and Higgs. 2010. PubMed ID: 20507641; Galanello and Cao. 2011. PubMed ID: 21381239).
Genetics
Two neighboring genes with high homology, HBA1 and HBA2, comprise the 4 alpha globin alleles. Classification of the different forms of alpha thalassemia is determined by the loss or inactivation of the alpha globin alleles.
Condition |
Genotype |
Silent Carrier |
-α/αα |
Alpha thalassemia trait |
-α/-α or --/αα |
Hemoglobin H |
--/-α |
Hemoglobin Bart Hydrops |
--/-- |
Deletions in the HBA1 and HBA2 genes are found in over 90% of alpha thalassemia cases with seven founder mutations accounting for ~85% of all alpha thalassemia cases: -α3.7, -α4.2, -(α)20.5, --SEA, --MED, --FIL, and –THAI. The -α3.7 and -α4.2 deletions result in loss of a single alpha globin gene whereas the -(α)20.5, --SEA, --MED, --FIL, and -–THAI deletions encompass both HBA1 and HBA2 genes. Several other loss of function variants including splicing alterations, insertions/deletions, and nonsense changes have been reported in both the HBA1 and HBA2 genes. Patients with non-deletional forms of alpha thalassemia often present with more severe disease. The most common structural variant found in Asian populations is Hemoglobin Constant Spring (HbCS) which abolishes the canonical termination codon in the HBA2 gene, c.427T>C (p.*143Gln) (Origa and Moi. 2016. PubMed ID: 20301608; Harteveld and Higgs. 2010. PubMed ID: 20507641; Galanello and Cao. 2011. PubMed ID: 21381239).
Clinical Sensitivity - Sanger Sequencing and MLPA
The most common pathogenic variant involving one or a few nucleotides found in Asian populations is Hemoglobin Constant Spring (HbCS) which abolishes the canonical termination codon in the HBA2 gene, c.427T>C (p.*143Gln). Missense, nonsense, insertions/deletions, splice site alterations, poly adenylation and promotor substitutions in the have been reported in the HBA1 and HBA2 genes. These pathogenic variants account for ~10% of all alpha thalassemia cases (Origa and Moi. 2016 PubMed ID: 20301608; Harteveld and Higgs. 2010. PubMed ID: 20507641; Galanello and Cao. 2011. PubMed ID: 21381239).
The -α3.7, -α4.2, -(α)20.5, --SEA, --MED, --FIL, and –THAI deletions account for ~85% of all pathogenic variants detected in alpha thalassemia patients. Other full gene deletions encompassing the HBA1 and/or HBA2 genes are found in ~<5% of cases (Origa and Moi. 2016 PubMed ID: 20301608; Harteveld and Higgs. 2010. PubMed ID: 20507641).
Testing Strategy
This test involves bidirectional sequencing using genomic DNA of all coding exons of the HBA1 and HBA2 gene plus ~10 bp of flanking non-coding DNA on each side as well as 5’ and 3’ untranslated regions, and the polyadenylation sequences. We will also sequence any single exon (Test #100) or pair of exons (Test #200) in patients and relatives of patients or to confirm research results.
Multiplex Ligation-Dependent Probe Amplification (MLPA) enables the detection of deletion and duplications of single and multiple exons within a given gene (Eijk-Van Os and Schouten. 2011. PubMed ID: 20938835). This test involves analysis only of the specific gene(s) of interest for each patient. The MLPA test is designed to have coverage for all exons for each targeted gene. It is a semi-quantitative technique to determine relative copy number using a multiplex PCR-based reaction. Only hybridized and ligated adjacent probe oligonucleotides of approximately 60 nucleotides in length are amplified using PCR and thus are specific for the sequence of interest. A stuffer sequence attached to the probe ensures a particular length for deciphering the probe target. Therefore, MLPA enables the detection of relatively small deletions and duplications within a single exon of a given gene or deletions and duplications encompassing the entire gene. For additional information please see www.mlpa.com.
Indications for Test
Patients with HbH present with anemia, splenomegaly, and mild jaundice. Laboratory findings include hypochromia (low mean corpuscular hemoglobin), microcytosis (low mean corpuscular volume) with detectable inclusion bodies, moderate reticulocytosis, decreased hemoglobin levels. Ideal candidates have HPLC or capillary electrophoresis indicating Hb patterns consistent with HbH or Hb Bart (Origa and Moi. 2016. PubMed ID: 20301608; Harteveld and Higgs. 2010. PubMed ID: 20507641).
Patients with HbH present with anemia, splenomegaly, and mild jaundice. Laboratory findings include hypochromia (low mean corpuscular hemoglobin), microcytosis (low mean corpuscular volume) with detectable inclusion bodies, moderate reticulocytosis, decreased hemoglobin levels. Ideal candidates have HPLC or capillary electrophoresis indicating Hb patterns consistent with HbH or Hb Bart (Origa and Moi. 2016. PubMed ID: 20301608; Harteveld and Higgs. 2010. PubMed ID: 20507641).
Genes
Official Gene Symbol | OMIM ID |
---|---|
HBA1 | 141800 |
HBA2 | 141850 |
Inheritance | Abbreviation |
---|---|
Autosomal Dominant | AD |
Autosomal Recessive | AR |
X-Linked | XL |
Mitochondrial | MT |
Diseases
Name | Inheritance | OMIM ID |
---|---|---|
Alpha Thalassemia | AR | 604131 |
Hemoglobin H Disease | AR | 613978 |
Related Test
Name |
---|
PGxome® |
Citations
Ordering/Specimens
Ordering Options
We offer several options when ordering sequencing tests. For more information on these options, see our Ordering Instructions page. To view available options, click on the Order Options button within the test description.
myPrevent - Online Ordering
- The test can be added to your online orders in the Summary and Pricing section.
- Once the test has been added log in to myPrevent to fill out an online requisition form.
- PGnome sequencing panels can be ordered via the myPrevent portal only at this time.
Requisition Form
- A completed requisition form must accompany all specimens.
- Billing information along with specimen and shipping instructions are within the requisition form.
- All testing must be ordered by a qualified healthcare provider.
For Requisition Forms, visit our Forms page
Specimen Types
ORDER OPTIONS
View Ordering Instructions1) Select Test Type
2) Select Additional Test Options
No Additional Test Options are available for this test.