Hb Isehara (or Hb Redondo) [β92(F8)HIS→SN]: An Unstable Variant with a Proximal Histidine Substitution at the Heme Contact

Abstract

A 50-year-old Japanese female patient was found to have hemolytic anemia. Isoelectrofocusing of her hemolysate revealed two abnormal hemoglobin bands, one of which was very close to the Hb A₂ band, and the other between the Hb A₂ and Hb F bands. CM-cellulose column chromatography of the globin prepared from the abnormal hemoglobin showed that the abnormal chain eluted faster than the normal β and δ chains; the β^X chain, however, did not separate from the normal β chain in urea cellulose acetate electrophoresis. An instability test of the patient's hemolysate revealed the presence of an unstable component. Structural analysis of the abnormal B chain indicated that the histidine residue at β92(F8) was replaced by an asparagine or aspartic acid residue. DNA amplified by poly-merase chain reaction was sequenced by the dideoxy method. The nucleotide sequence of the β92 codon was AAC instead of CAC, suggesting that the amino acid substitution corresponded to His→tAsn, which is the same as is found in Hb Redondo or ∼92(F8)His→Asn→Asp.