β-Thalassemia: HBB (Full Gene Sequencing)

Whole blood or LabCorp buccal swab kit (buccal swab collection kit contains instructions for use of a buccal swab); DNA is also accepted. (Call 800-345-4363 for DNA collection information.)

7 mL whole blood or 4 buccal swabs

3 mL whole blood or 2 buccal swabs

Lavender-top (EDTA) tube or LabCorp buccal swab kit

Confirm a clinical diagnosis of β-thalassemia; detect carriers; help to establish a prognosis

This method does not reliably detect mosaic variants, deep intronic variants, large deletions, large duplications, inversions or other rearrangements. Assay results may be affected by the presence of homopolymer repeats or by allele-dropout due to sequence polymorphisms in primer binding sites. This assay does not allow any conclusion as to whether two heterozygous variants are present on the same or on different chromosome copies.

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

DNA sequencing

Normal equals reference sequence or variants that are known or predicted to be benign; abnormal equals all other variants.

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.