Hb A2′ (Hb B2) in the Omani population and diagnostic significance

Hb A2′ [δ16(A13)Gly→Arg], also called Hb B2, is a δ-globin chain variant that has been identified in several populations of African origin or ancestry and is easily identifiable in alkaline acetate cellulose electrophoresis as doubling of the Hb A2 band. However, in high performance liquid chromatography (HPLC), commonly employed nowadays, it elutes in the S window. Over a period of 2 years at the Sultan Qaboos University Hospital, Muscat, Oman, we identified 25 Omanis with this variant. The quantity of Hb A2 ranged from 0.9 to 1.8% in heterozygotes and was undetectable in the single homozygous case. As both α- and β-thalassemia (α- and β-thal) as well as Hb S [β6(A3)Glu→Val] are common in the Omani population, it is important to be aware of the presence of Hb A2′ in this population to avoid misinterpretation of the HPLC data in terms of underdiagnosis of β-thal carriers and overestimation of α-thal based on Hb A2 levels in sickle cell carriers. The haplotype associated with Hb A2′ in Oman is identical to that described in African populations, suggesting a common origin for this mutation and its introduction into Oman by gene flow.