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Studies of some mutants of human hemoglobin including a new oC-variant: Hb mahidol Pootrakul, Sanga

Abstract

Hemoglobinopathies, the disorders of hemoglobin structure and synthesis, can be divided into two forms of clinical manifestation, namely thalassemias and abnormal hemoglobins. Thalassemia appears to involve an abnormal gene which results in a reduced rate of globin synthesis and it presents clinically as a hypochromic microcytic anemia. Its cause lies in some abnormality of the regulation of globin synthesis. An abnormal hemoglobin is usually the result of a mutation of one base in a codon triplet of the structural gene for one or other hemoglobin chain which leads to an amino acid substitution in the primary structure of the globin. In this study, the biochemical characterization of five samples of abnormal hemoglobin which were obtained from patients at Vancouver General Hospital, Vancouver, B.C. and Siriraj Hospital, Bangkok is described. In the first case from V.G.H., the propositus, a 17 month old Chinese girl showed a fast (anionic) abnormal hemoglobin from birth. In a biochemical investigation of the variant from her father it was found that the glycine residue 56 in the β-chain was substituted by aspartic acid. This mutant is identical to that previously designated as HbJ Bangkok ([formula omitted]). The second case, a 21 year old Thai male in Bangkok was shown to be a double heterozygote with both a slow and a fast abnormal hemoglobin and an absence of HbA upon starch gel electrophoresis. Structural characterization of the separated globin chain of both variants indicated that the mutation in the slow variant occurred at residue 26 of β-chain where glutamic acid was replaced by lysine. This mutation is similar to that previously described as HbE ([formula omitted]). The fast variant showed an amino acid alteration at position 113 of β-chain where valine was substituted by glutamic acid. This mutation is identical with Hb New York ([formula omitted]). A double heterozygote involving both HbE and Hb New York has not been previously described. The other three samples from unrelated patients in Bangkok revealed a slow mutant on starch gel electrophoresis and biochemical studies showed that residue 74 in the α-chain was changed from an aspartyl to a histidyl residue. This mutation has not been previously described. It is proposed that this new hemoglobin ([formula omitted]) be called Hb Mahidol after Mahidol University in Bangkok. In one of the three patients showing Hb Mahidol interaction with α-thalassemia (α-thalassemia-Hb Mahidol) occurs. This results in the clinical features of chronic hemolytic anemia and a total absence of HbA which is replaced by Hb Mahidol together with some HbH([formula omitted]).

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