New and Known β-Thalassemia Determinants Masked by Known and New δ Gene Defects [Hb A2-Ramallah or δ6(A3)Glu→Gln, GAG>>CAG

Abstract

We report a novel thalassemia determinant found in a Nigerian woman living in the Netherlands, resulting from a 2 bp insertion at codons 9/10 of the β-globin gene (HBBc.28_29insTA p.Ser10LeufsX11). The novel defect causes a frameshift with a consequent premature TGA stop codon, located at 11 positions downstream from the mutated codon. The phenotype was typical of a β-thalassemia (β-thal), trait with high RBC counts and compensated mild microcytic anemia. However, the Hb A2 level was reported to be normal due to the presence of the common Hb A2' or Hb B2 [δ16(A13)Gly→Arg, GGC>CGC] variant that was not taken into account. We also present the opposite but comparable situation found in an a Palestinian man living in the USA. He was a carrier of a common β-globin gene defect [codon 6 (–A), HBB:c.20delA] in combination with a novel δ-globin gene defect at codon 6 [HBD. c.19G>C, Glu6Gln] that we have named Hb A2-Ramallah. In both cases, the provisional diagnosis could have been compromised when based on the measurement of the normal Hb A2 fraction only.