First Description of a Hb A₂ Variant in Thailand. Identification of Hb A₂-Melbourne [δ43(CD2)Glu→Lys] in Thai Individuals

Abstract

We report the molecular and hematological identifications of a Hb A₂ variant found for the first time in Thailand. The subjects were two unrelated Thai women who had normal hematological features. In the first case, hemoglobin (Hb) high performance liquid chromatography (HPLC) analysis identified, in addition to Hb A, Hb A₂ (1.6%) and a minor Hb variant (0.9%) separating after Hb A₂. Analysis using capillary electrophoresis (CE) demonstrated 1.3% Hb A₂ and 1.0% minor variant in zone 1. DNA analysis showed a single nucleotide mutation at codon 43 of the δ-globin gene (HBD:c.130G>A) causing a glutamic acid to lysine substitution corresponding to Hb A₂-Melbourne, originally documented in an Italian subject, but not previously described in Thailand. The mutation could be confirmed by allele specific polymerase chain reaction (PCR) assay. Further screening using this technique in our series identified another case of a Thai woman with a double heterozygosity for Hb A₂-Melbourne and α⁺-thalassemia (α⁺-thal). A β-globin gene haplotype associated with this Thai Hb A₂-Melbourne gene was also established.

• Hb A₂-Melbourne
• δ-Globin chain variant
• Hemoglobinopathies