Haemoglobinopathies That Occur with Decreased HbA2 Levels: a Gene Mutation Set Involving the δ Gene at a Spanish Centre

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

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

Conclusion: HbA is an essential parameter in the diagnostics of haemoglobinopathies. HPLC-EC and CZE allow the quantification of HbA. Here, we show that quantification of HbA 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.