RT Journal Article SR Electronic T1 Dominant β-thalassaemia with unusually high Hb A2 and Hb F caused by βCD121(−G) (HBB:c.364delG) in exon 3 of β-globin gene JF Journal of Clinical Pathology JO J Clin Pathol FD BMJ Publishing Group Ltd and Association of Clinical Pathologists SP 511 OP 513 DO 10.1136/jclinpath-2019-206308 VO 73 IS 8 A1 Kritsada Singha A1 Rossarin Karnpean A1 Goonnapa Fucharoen A1 Supan Fucharoen YR 2020 UL http://jcp.bmj.com/content/73/8/511.abstract AB We describe a dominant β-thalassaemia caused by a deletion of G at nucleotide position 364 in exon 3 of the β-globin gene. The heterozygosity of this mutation was found in a 36-year-old Thai patient who had moderate hypochromic microcytic anaemia with haemolytic blood picture. Haemoglobin (Hb) analysis revealed relatively higher Hbs A2 (6.8%) and F (4.7%) as compared with those of β0-thalassaemia (n=278) and β+-thalassaemia (n=55) carriers in our series. Secondary structure prediction of the elongated β-globin chain showed that the α-helix at the C-terminal is disrupted dramatically by the random coil and β-sheet, which should result in a highly unstable β-globin variant, undetectable in peripheral blood and a dominant clinical phenotypic feature.