Hb Feilding [β12(A9)Thr → Pro; HBB: c.37A>C]: a novel unstable β-globin chain variant

We report here a patient heterozygous for a previously unreported β chain variant. A 72-year-old Caucasian female was found to have an abnormal hemoglobin (Hb) as an incidental finding following Hb A1C analysis. There was no family history of anemia or hemoglobinopathy. Her full blood count revealed a mild normochromic anemia with Hb 11.1 g/dL (range 11.5-15.0), mean corpuscular volume (MCV) 93.0 fL (range 80.0-100.0) and mean corpuscular Hb (MCH) 30.0 pg (range 27.0-32.0). Isopropanol stability tests and a variant Hb on high performance liquid chromatography (HPLC) comprizing 37.0% of the total Hb suggested an unstable Hb variant. Sanger sequencing of the β-globin gene revealed a single base substitution, HBB: c.37A>C, causing the missense mutation β12(A9)Thr → Pro in exon 1 of the HBB gene. This mutation changes the threonine residue at position 12(A9) to a proline in the β-globin chain. We propose that this variant be called Hb Feilding after the town where the proband lived. Three dimensional modeling suggested that the disruption of the Hb structure was due to the introduction of a proline at helix A9 which caused distortion of the helical structure and resulted in reduced solubility.