Thalassemia intermedia associated with the Hb Constant Spring EE Bart's disease in pregnancy: A molecular and hematological analysis

Abstract

We defined the molecular basis and analyzed hematological phenotype associated with an unusual form of thalassemia intermedia caused by interaction of the hemoglobin Constant Spring (Hb CS), homozygous Hb E and α°-thalassemia found in two unrelated pregnant Thai women. Both patients had moderate anemia and characteristic of thalassemia intermedia. Hb-HPLC analysis demonstrated in both cases, Hb E and Hb Constant Spring with 3–4% Hb Bart's. Hb F was marginally elevated (3–5%). Both of them were diagnosed hematologically as the Hb CS EE Bart's disease. DNA analysis revealed the homozygosity for Hb E in both cases and identified the Hb CS mutation in trans to the α°-thalassemia allele with the SEA deletion in one case and with the Thai deletion in another. The appearance of Hb-HPLC peak resembling the Hb CS in peripheral blood of the two cases indicated the ability to form a tetrameric Hb molecule between α CS and β E chains leading to a hybrid Hb namely the Hb E-CS (α 2 CSβ 2 E) with similar characteristics to Hb CS (α 2 CSβ 2 A). Hematological data of the patients were presented comparatively with other forms of related disorders in our series including 2 Hb H/Hb EE diseases, 16 homozygous Hb CS with and without Hb E, 14 Hb H diseases and 35 Hb H-CS diseases. Different genotype–phenotype correlations observed in these Thai patients with these disorders are illustrated.