Hemoglobin Hobart or α 20(B1)His → Arg: A New α Chain Hemoglobin Variant

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Abstract
A new a chain hemoglobin variant, Hb Hobart, α20(Bl)His → Arg, was detected in a 60-year-old female of British nationality. The proposita had a history of severe rheumatoid arthritis and had been treated for many years for a refractory microcytic anemia and/or iron deficiency. A hemoglobin electrophoresis screen indicated the presence of a hemoglobin variant, with electrophoretic characteristics similar to a Hb Lepore. However, the level of the variant (17.9%) and the presence of a minor variant Hb A2 band (0.4%) suggested that further investigation was indicated. The variant hemoglobin was purified by column chromatography and the a chain subjected to aminoethylation and tryptic digestion. Peptide mapping and amino acid analysis indicated that the histidine residue 20 had been substituted by an arginine residue. The substitution in Hb Hobart is at the first residue in the B Helix of the α chain of hemoglobin. As this is an externally placed amino acid in the hemoglobin molecule, a substitution at this position of the hemoglobin molecule would not be expected to cause any functional problems. A family study has shown that at least three other relatives are heterozygous for Hb Hobart. These family members have normal hematological findings.