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

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 β(0)-thalassemia (β(0)-thal) mutations. She was also found to have a low Hb A(2) 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) β(0)-thal mutation. Doubling the amount of hemolysate loaded for chromatography revealed a widened Hb A(2) 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 A(2) level for phenotypic diagnosis of β(0)-thal trait.