Association in cis of β+-thalassemia and hemoglobin S

A Moroccan woman was investigated because of a typical β-thalassemia trait associated with a low-percentage (11%) hemoglobin (Hb) variant. The β-thalassemia trait was manifested by a microcytosis, a high HbA2 (above 6%), and an increase of the α/β biosynthetic ratio (1.31). The variant was identified to HbS by amino acid analysis of the abnormal peptide (β T1) and by DNA mapping with Sau I (Mst II) restriction endonuclease. No additional amino acid substitution was recorded in the βs-chain. The reduction of β-globin synthesis occurred exclusively at the expense of the βs-chain. These results are consistent with the existence of a βs mutation and a β+-thalassemia in cis.