Elevated Hemoglobin A₂: A Molecular Revisited, and Implications to β-Thalassemia Screening

Area of Science:

• Hematology
• Genetics
• Molecular Biology

Background:

• Thailand revised its HbA2 cutoff for beta-thalassemia carrier screening from 4.0% to 3.6% in 2015.
• This study investigates the impact of this change on the molecular characterization of beta-thalassemia in a large Thai cohort.

Purpose of the Study:

• To examine the molecular basis of beta-thalassemia following the HbA2 cutoff adjustment in Thailand.
• To identify and characterize beta-thalassemia mutations in a significant population sample.

Main Methods:

• Retrospective analysis of 36,313 specimens collected between January 2016 and June 2025.
• Recruitment of 5909 subjects with HbA2 levels ≥ 3.6% for further Hb and DNA analyses.

Main Results:

• Fifty distinct beta-thalassemia genes were identified, including nine previously unreported in Thailand and two novel mutations: beta(CD81(CTC > CTA)) and beta(IVSII-713(G > A)).
• Misinterpretation of borderline HbA2 levels accounted for a significant portion of discrepancies, with falsely elevated HbA2 observed in 70.8% of misinterpreted cases.
• The study observed a higher prevalence of beta-thalassemia positive (beta+) compared to beta-thalassemia (beta0) mutations, alongside normal beta-globin genes and diagnostic errors at borderline HbA2 levels.

Conclusions:

• The revised HbA2 cutoff has influenced the observed molecular spectrum of beta-thalassemia in Thailand.
• The updated molecular profile now includes 50 identified mutations, encompassing both known and novel variants.
• Attention to misinterpretations at borderline HbA2 levels and cost-effectiveness are crucial considerations for beta-thalassemia screening programs in the region.