Association of Hb A₂ Variants with Several Forms of α- and β-Thalassemia in Thailand

Abstract

In this study, Hb A₂ variants and their association with α- and β-thalassemia (α- and β-thal) were analyzed. We performed molecular analyses to identify α-thal [– –^SEA (Southeast Asian), – –^THAI (Thai), –α^3.7 (rightward) and –α^4.2 (leftward)] deletions, and Hb Constant Spring (Hb CS; HBA2: c.427T>C), Hb A₂-Melbourne (HBD: c.130G>A), Hb A₂′ (HBD: c.49G>C), Hb A₂-Lampang (HBD: c.142G>A). β⁰-Thalassemia mutations included codon 17 (A>T) (HBB: c.52A>T), codons 41/42 (–TCTT) (HBB: c.126_129delCTTT), codons 71/72 (+A) (HBB: c.216_217insA) and IVS-I-1 (G>T) (HBB: c.92+1G>T) in 23 samples which had a Hb A₂ variant peak in zone 1 of the capillary electrophoresis (CE) electropherogram. Results showed that 20 patients (87.0%) carried Hb A₂-Melbourne with seven different genotypes for α- and β-thal, two (8.7%) carried Hb A₂′ and one (4.3%) carried Hb A₂-Lampang. All three samples doubly heterozygous for Hb A₂-Melbourne/β⁰-thal had Hb A₂ levels lower than 4.0%, while summation of Hb A₂ and Hb A₂-Melbourne ranged from 4.9–5.3%, reaching the accepted range (4.0–10.0%) for β-thal trait. Hb A₂-Melbourne is the most common δ-globin variant in the Thai population. Hb A₂ variant and Hb A₂ levels must be combined in order to diagnose carriers of β-thal. β-Globin haplotype analysis showed an association with a single β-globin haplotype [+ – – – – + +] of Hb A₂-Melbourne, Hb A₂′ and Hb A₂-Lampang, indicating that they were of the same origin. We developed a multiplex allele-specific polymerase chain reaction (ASPCR) for simultaneous detection of these three Hb A₂ variants.

Keywords:

• α-Thalassemia (α-thal)
• β-thalassemia (β-thal)
• coinheritance
• haplotype
• Hb A₂ variants

Acknowledgments

The authors thank Mrs. Kallayanee Treesuwan Rock, Associated Medical Sciences-Clinical Service Center, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai, Thailand, for refinement of the English language.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Additional information

Funding

This research project was supported by a grant from University of Phayao, Phayao, Thailand [Gant No. RD61075].