Molecular and structural characterization of a novel β-hemoglobinopathy caused by in Cis β-globin mutations in a Thai individual

Abstract

Hemoglobin (Hb) E is the most common Hb variant in Southeast Asia. We described a novel form of Hb E caused by an in cis combination of Hb E and another β-hemoglobinopathy affecting Hb stability. Study was done on a Thai woman at a routine prenatal screening of thalassemia. Hb analysis was carried out by HPLC and capillary electrophoresis. Mutation and β-globin gene haplotype analyses were done using PCR-based assays. Structure of the abnormal Hb molecule was predicted using molecular dynamics simulations. The subject had mild normocytic anemia with Hb 10.3 g/dL. Hb-HPLC analysis revealed Hb A<inf>2</inf>A with 6.9% Hb A<inf>2</inf>, whereas capillary electrophoresis showed Hb A<inf>2</inf>EA with 3.6% Hb A<inf>2</inf> and 3.4% Hb E. No α- and β-thalassemia mutations were detected. Further β-globin gene analysis identified a novel variant caused by two in cis mutations, i.e., Hb E (codon 26 GAG > AAG) and Hb Palmerston North (codon 23 GTT > TTT), namely Hb E-Hb Palmerston North. Splicing site prediction of the Hb E-Palmerston North gene showed similar splicing scores at both normal and cryptic splice sites with those of the Hb E gene. System stability prediction of the Hb E-Palmerston North expression indicated a weakening αβ contact, resulting in instability and a dramatic reduction of Hb variant (3.4%). The novel Hb E variant, designated Hb E-Palmerston North, was characterized by unusually low levels, which was attributed to its high instability. The diagnosis of this novel Hb variant is best by multiplex PCR assay developed.