Hemoglobin Windsor or β11(A8)Val→Asp: A new Unstable β-Chain Hemoglobin Variant Producing a Hemolytic Anemia

Abstract

A new β-chain variant, Hemoglobin Windsor [β11(A8)Val→Asp] was discovered in a 9-month-old child who presented with a hemolytic anemia of 59 g/1 with an intercurrent viral infection. Her blood film demonstrated fragmented cells, target cells, stipple cells, nucleated red cells, polychromasia and some spherocytes, indicative of acute hemolysis. Hemoglobin electrophoretic studies were requested and a β-chain variant, constituting 27% of the total hemoglobin, separated towards the anode under alkaline conditions. The variant was unstable, producing numerous “Hb H”-like inclusions and a positive isopropanol stability test. The variant hemoglobin was purified by precipitation. The variant β-chain was purified by column chromatography and its tryptic peptides fractionated by high performance liquid chromatography. Amino acid analysis and sequence data indicated that the valine at position 11(A8) had been substituted by an aspartic acid residue. This substitution, in the bottom of the heme pocket, has resulted in instability of the hemoglobin molecule and an increase in oxygen affinity.