Alpha Thalassemia

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This test detects the 5 major deletions that cause α-thalassemia. These are the rightward and leftward one α-globin gene deletions (αα/-α) and the 2 α-globin gene in cis deletion (--/αα) resulting from the Southeast Asian, Filipino and Thai deletions.

The most clinically significant situation arises when each parent is a carrier of a 2-α globin gene deletion in cis (--/αα). Fetuses of such couples are at 25% risk for hydrops fetalis. Matings between carriers of a 2 α-globin gene deletion and single α-globin gene deletion are at risk for Hb H disease (--/-α).

This test is often used to assess whether a low MCV is caused by the inheritance of α-thalassemia either alone or in combination with iron deficiency and/or α-thalassemia.

This test does not detect α-thalassemia due to a point mutation.

Please fill out and send with the sample the Thalassemia Request Form

β-Globin Gene Sequencing

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When a low MCV associated with an elevated HbA2 fails to detect a β-globin mutation with our β-thalassemia mutations panel, then DNA sequencing of the β-globin gene can usually uncover the underlying mutation.

This test is appropriate following a negative result with the common β-thalassemia mutation panel test and a strong suspicion of β-thalassemia.

β-thalassemia

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Over 300 mutations have been reported to cause β-thalassemia. Our test detects a panel of common mutations among Mediterranean, Asian and African chromosomes using PCR and allele-specific probes in the reverse dot blot hybridization format. The mutation panel is summarized below.

This test is primarily used to detect mutations in the beta globin gene in one or more of the following settings:

• To delineate mutations for prenatal diagnosis.
• To confirm the diagnosis of β-thalassemia when an elevated Hb A2 is detected.
• To confirm that a low MCV is caused by β-thalassemia.
• To determine whether iron deficiency and β-thalassemia interact in the presence of a low MCV.

Please fill out and send with the sample the Thalassemia Request Form

β⁰ Mutations

• Codon 5(-CT)
• Codon 6(-A)
• Codon 8(-AA)
• Codon 8/9(+G)
• Codon 14/15(+G)
• Codon 15(GG-AG)
• Codon 15(GG-GA)
• Codon 16(-C)
• Codon 17(A-T)

• Codon 26(G-T)
• Codon 27/28(+C)
• Codon 30(AGG-ACG)
• Codon 36/37(-T)
• Codon 37(GG-GA)
• Codon 39(C-T)
• Codon 41/42(-CTTT)
• Codon 43(G-T)
• Codon 44(-C)

• Codon 51(-C)
• Codon 67(-TG)
• Codon 71/72(+A)
• Codon 95(+A)
• Codon 106/107(+G)
• Codon 121(G-T)
• Codon 11(-T)
• Codon 15(-T)
• Intitiation codon (T-G)

• IVSI-1(G-A)
• IVSI-1(G-T)
• IVSI-2(T-A)
• IVSI-2(T-C)
• IVSII-1(G-A)
• IVSII-849(A-G)
• IVSII-850(G-T)

β⁺ Mutations

• -90(C-T)
• -88(C-T)
• -87(C-G)
• -30(T-A)
• -29(A-G)

• -28(A-C)
• -28(A-G)
• Codon 24(T-A)
• Codon 27(G-T)
• Codon 29(C-T)

• IVSI-5(G-C)
• IVSI-5(G-A)
• IVSI-6(T-C)
• IVSI-110(G-A)
• IVSII-654(C-T)

• IVSII-745(C-G)
• IVSII-848(C-A)
• Poly A(T-C)
• Poly A(A-G)

Hemoglobin Variants

• Hb S: Codon 6(A-T)
• Hb E: Codon 26(G-A)

• Hb C: Codon 6(G-A)
• Hb D: Codon 121(G-C)

Hemoglobin Constant Spring

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Hemoglobin Constant Spring is an α-chain variant whereby the termination codon TAA is mutated to CAA which encodes the amino acid glutamine. This point mutation results in an extension of the α-globin chain to 172 amino acids. This mutation is common amongst Southeast Asians and can occur along with a two α-globin gene deletion in cis thus causing Hemoglobin H disease.

Hemoglobin S, C, E

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These hemoglobin variants may be inherited with α or β-thalassemia and may occasionally be obscured by the presence of elevated Hb A2 or Hb F or by their position in traditional hemoglobin electrophoresis.