Hemoglobin H Disease Classification by Isoelectric Focusing: Molecular Verification of 110 Cases from Thailand

Abstract

Hemoglobin (Hb) H disease is a mild to severe form of α-thalassemia caused by the absence/inactivation of three of four α-globin genes. As a result, there are insufficient α-globin chains to form HbA (α2β2), the excess β-globin chains forming unstable HbH (β4) (1), which precipitates and attaches to the erythrocyte membrane to cause membrane dysfunction and hemolysis (2). Genetically, there are two types of HbH disease, deletional HbH disease caused by compound heterozygosity for a double α-globin gene deletion on one chromosome and a single α-globin gene on the other (−α/− −), and nondeletional HbH disease caused by compound heterozygosity for a double α-globin gene deletion and a point mutation or small deletion/insertion on a third α-globin gene (αTα/− − or ααT/− −) (2). Generally, patients with nondeletional HbH disease present with a more severe phenotype than those with deletional HbH disease (1)(2). HbH disease is particularly prevalent in Southeast Asia because of the high frequency of α-thalassemia carriers in these areas (1)(2). In northern Thailand, ∼1.5% (1 in 65) of babies are expected to be born with HbH disease (3). In addition, nondeletional HbH disease with αConstant Spring (HbHCS) is very common in Thailand, where ∼40–50% of patients with HbH disease have nondeletional HbH with αConstant Spring (4). Since the 1980s, isoelectric focusing (IEF) has been widely used in the identification of hemoglobin variants and in the diagnosis of HbH disease and HbBarts hydrops fetalis because of the good separation of HbBarts, HbH, and HbCS tetramers in IEF gels. The accuracy of IEF in HbH disease classification, however, is unknown. To evaluate the accuracy of IEF in predicting α-globin genotype, we analyzed the genotypes of 110 Thai patients identified as having either deletional …