Hb A₂ Hong Kong – A Novel δ-Globin Variant in a Chinese Family Masks the Diagnosis of β-Thalassemia Trait

Abstract

A 42-year-old Chinese woman (FP) was the mother of a patient with β-thalassemia major (β-TM) due to a compound heterozygosity for β⁰-thalassemia (β⁰-thal) mutations. She was also found to have a low Hb A₂ level of 1.6% by high performance liquid chromatography (HPLC) despite being a heterozygous carrier of the codons 41/42 (–TCTT) (HBB:c.126_129delCTTT) β⁰-thal mutation. Doubling the amount of hemolysate loaded for chromatography revealed a widened Hb A₂ peak and raised the level to 4.1%, consistent with β-thal trait. Direct nucleotide sequencing detected a novel δ-globin gene mutation at codon 29 (HBD:c.89G>A), which leads to a glycine to aspartic acid substitution. A homologous mutation at codon 29 in the β-globin gene [Hb Lufkin or β29(B11)Gly→Asp] has been reported in Black families. This report highlights the importance of genotype-phenotype correlation and the potential pitfall of relying on Hb A₂ level for phenotypic diagnosis of β⁰-thal trait.

• δ-Globin variant
• Masked β-thalassemia (β-thal)
• Chinese