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

Abstract

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.

• Hb A_1C
• hemoglobin (Hb) mutation
• mass spectrometry (MS)
• unstable hemoglobin (Hb)

Acknowledgements

We wish to thank Mr. Charles Hawes, Canterbury Health Laboratories, Christchurch, New Zealand, for technical assistance.