Hb Ashburton [β12(A9)Thr → Pro; HBB: c.37A > C], a Novel,Mildly Unstable Variant and the First Substitution Identified at Codon 12

We report the identification of a novel, slightly unstable hemoglobin (Hb) variant [β12(A9)Thr?→?Pro; HBB: c.37A?>?C] that came to our attention during Hb A_1C ion exchange chromatography where it migrated as a trailing shoulder on the Hb A₀ peak. On electrospray ionization mass spectrometry (ESI MS), this electrophoretically silent variant was detected as an unresolved β component with a 2?Da decrease in average β chain mass. Reversed phase high performance liquid chromatography (HPLC) confirmed the presence of a more hydrophilic β chain with a mass 4?Da less than normal β^A and showed it represented 40.0% of the total β-globin. Tryptic mapping revealed the [M?+?1H] ion of peptide βT-2 had shifted from 932.5 to 928.5 m/z, suggesting a point mutation of Thr?→?Pro at position β12(A9). This substitution was confirmed by fragmentation analysis of the [M?+?2H] ion (464.8 m/z) of the new βT-2 peptide and it represents a novel mutation which we have named Hb Ashburton.     

Detection of Hb A2 and Hb Constant Spring (HBA2: c.427T>C) by Capillary Electrophoresis in a Patient with Hb H-Hb CS Disease

Abstract

Hb A₂ (α2δ2) is one of the key components looked for in hemoglobinopathies screening programs. Therefore, quantitative and accurate method for Hb A₂ value determination is essential for routine screening. Here, we report a case of Hb A₂ and Hb Constant Spring (Hb CS, HBA2: c.427T>C) with Hb H-Hb CS disease that was not detected by high performance liquid chromatography (HPLC), while Hb A₂ and Hb CS were clearly quantified by capillary electrophoresis (CE).     

Analysis of the Genotypes in a Chinese Population with Increased Hb A2 and Low Hematological Indices

Abstract

Increased Hb A₂ is considered the most reliable hematological finding for the identification of β-thalassemia (β-thal) carriers. The aim of this study was to determine the underlying genetic factors associated with a high Hb A₂ level in a Chinese population. Subjects were recruited from couples preparing for pregnancy who participated in the thalassemia screening program during a 2-year period. DNA analyses were used for diagnosis of β-thal and other genetic factors. A total of 5985 adults who screened positive for β-thal were recruited. Of these, 5933 (99.1%) were detected to have a β-thal mutation. In the remaining 52 (0.9%) individuals without mutations involving the β-globin gene cluster, 16 were found to have Krüppel-like factor 1 (KLF1) gene variants, and two had an α-globin gene triplication. There were still 34 individuals with unknown genetic factors for their raised Hb A₂ values. The results of this study indicate that genetic factors other than β-thal can rarely contribute to the elevation of Hb A₂. These subjects usually have borderline microcytic red cell indices and Hb A₂ values.