Hb A₂′ (Hb B2) in the Omani Population and Diagnostic Significance

Abstract

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.

• β-Thalassemia (β-thal)
• Oman
• Hb A₂′
• Hb S