Polycythaemia associated with homozygosity for the abnormal haemoglobin Sherwood Forest (beta 104 (G6)Arg-->Thr).

We describe a 22-year-old Pakistani male with polycythaemia associated with homozygosity for a high-affinity haemoglobin mutant, Hb Sherwood Forest. This haemoglobin variant has an amino acid substitution in the beta globin chain at position 104, Arg-->Thr. In the two previously reported instances of this haemoglobin mutant the individuals were heterozygotes and were haematologically normal. We show here that the homozygous state for the mutation is associated with a compensatory erythrocytosis resulting from decreased delivery of oxygen to the tissues. A family study showed that both parents and two siblings are heterozygotes for the haemoglobin mutant and are haematologically normal. To our knowledge, this represents the first example of a beta-globin mutation producing polycythaemia in homozygotes but not in heterozygotes.