Aims Haemoglobin A₂ (HbA₂) consists of two globin chains, α and β. Alterations in any of these genes influences the level of HbA₂. Here, we present cases of structural Hb variants and thalassaemias which present either alone or together and reduce the level of HbA₂ at varying degrees. Furthermore, we present a novel structural mutation in the δ globin gene, called Hb A₂-Madrid.

Methods The levels of HbA₂ and HbF and the different haemoglobin variants were measured and analysed by ion exchange high performance liquid chromatography (HPLC, VARIANT II), the types of haemoglobins were determined by capillary zone electrophoresis (CZE) (Sebia) and the globin chains were determined by reversed-phase HPLC. Genetic analysis was performed by automatic sequencing of the α and δ genes as well as by multiple PCRs for the α globin genes.

Results In α thalassaemia (n=94), the HbA₂ levels ranged from 1.39% to 2.43%. Among individuals with δ thalassaemia (n=5), the HbA₂ level of those with δ⁺ thalassaemia was 1.77%, and that of those with δ⁰ thalassaemia was 1.70%. Among the individuals with δβ thalassaemia (n=13), those who were homozygous lacked HbA₂. All structural haemoglobinopathies (n=97) were heterozygous; the α chain variants (n=84) presented with an HbA₂ level of 1.76%, while the δ chain variants (n=13) presented with a level of 1.75%.

Conclusion HbA₂ is an essential parameter in the diagnostics of haemoglobinopathies. HPLC-EC and CZE allow the quantification of HbA₂. Here, we show that quantification of HbA₂ is critical for the identification of α, δ and βδ thalassaemias. Structural variants are discovered by HPLC. Molecular genetics is required for the proper identification of the mutations. Only with this knowledge is genetic counselling possible.