| Interpretive Data: |
Background Information for Alpha Thalassemia (HBA1 & HBA2) Sequencing:
Characteristics: Alpha thalassemia, caused by insufficient or absent alpha chain production, has a highly variable clinical presentation. Classic deletional alpha thalassemia may result in:
Alpha thalassemia silent carrier; mutation of a single alpha globin gene (-a/aa); typically asymptomatic.
Alpha thalassemia trait; mutation of two globin genes in trans (-a/-a), or cis ( --/aa); mild microcytic anemia possible.
Hemoglobin H disease; mutation of three alpha globin genes (--/-a); hemolysis with Heinz bodies, moderate anemia, splenomegaly.
Hemoglobin Bart hydrops fetalis syndrome; mutation of four alpha globin genes (--/--); lethal in fetal or early neonatal period.
Non-deletional alpha thalassemia may result in more severe phenotypes.
Incidence: Carrier frequency in Mediterranean (1 in 30 to 1 in 50), Middle Eastern, Southeast Asian (1 in 20), African, African-American (1 in 3).
Inheritance: Autosomal recessive.
Cause: Deleterious HBA1 or HBA2 gene mutations.
Clinical Sensitivity: Up to 10 percent. Most HBA1 and/or HBA2 gene mutations are large deletions not detectable by sequencing.
Methodology: Bidirectional sequencing of the entire HBA1 and HBA2 coding region and intron-exon boundaries, proximal promoter region, 5' and 3' untranslated regions, and polyadenylation signal.
Analytical Sensitivity and Specificity: 99 percent.
Limitations: Rare diagnostic errors can occur due to primer site mutations. Large deletions/duplications and some mutations of the regulatory regions, will not be detected. Phase of identified mutations may not be determined. Rare syndromes associated with alpha thalassemia such as ATR-X and ATR-16 will not be detected.
Please refer to Statement C in the Compliance Statements section in the front of the Laboratory Test Directory.
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| Note: |
For detection of the seven most common deletions, refer to Alpha Thalassemia, HBA1 & HBA2 Gene Deletions (0051495).
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| CPT Code(s): |
83891 Isolation; 83898 x2 Amplification; 83904 x6 Sequencing; 83909 capillary electrophoresis; 83912 Interpretation and report - Additional CPT code modifiers may be required for procedures performed to test for oncologic or inherited disorders.
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