Hb Malmö [β-97(FG-4)His→Gln] leading to polycythemia in a Dutch family

Abstract

 We have examined six individuals from a two-generation Dutch family for a suspected hemoglobin (Hb) abnormality. The propositus presented with polycythemia and complained of persistent weakness, headache, and epistaxis. All family members initially showed a normal Hb-electrophoretic pattern, but on isoelectric focusing, three of them displayed a fast-moving band associated with high packed red cell volumes (PCV) and increased red blood cell count. The Hb mutant was analyzed at the DNA level by specific gene fragment amplification (PCR), followed by direct DNA sequencing, and the mutation was confirmed by restriction enzyme analysis. We found a C→G transversion (CAC→CAG) at codon 97 of the β-chain, which corresponded to the His→Gln amino acid substitution previously described as Hb Malmö. We report here the clinical history of the patient, the effects of phlebotomy treatment, and the effect of subnormal iron conditions on the erythropoietic recovery after phlebotomy. The mechanism responsible for the induction of the higher oxygen affinity is discussed, as are some aspects concerning the occurrence, pathology, treatment, and the genetic risk of Hb variants with high O₂ affinity.