Hb Trollhättan [beta 20(B2)Val-->Glu]--a new haemoglobin variant with increased oxygen affinity causing erythrocytosis.

Erythrocytosis is sometimes caused by the presence of haemoglobin (Hb) variants with increased oxygen affinity. Here we describe a beta-globin variant found by isoelectric focusing (IEF) of Hb from a 23-year-old Swedish male with moderate erythrocytosis. Amplification of DNA corresponding to the beta-globin gene and subsequent nucleotide sequencing revealed heterozygosity for a GTG-->GAG mutation at codon 20, thus suggesting a Val-->Glu substitution, which was confirmed at the protein level. This mutation occurs at the same position as Hb Olympia [beta 20(B2)Val-->Met], another variant associated with erythrocytosis due to increased oxygen affinity. The novel variant, Hb Trollhättan [beta 20(B2)Val-->Glu], which was also associated with increased oxygen affinity, was shown to be present in three generations of the patient's family.