Haematological and clinical features of β-thalassaemia associated with Hb Dhofar

Hb Dhofar is a variant haemoglobin (β^{29 (GGC-GGT) gly-gly}, β^{58 (CCT-CGT) pro-arg}) associated with a thalassaemic phenotype and unique to the Sultanate of Oman. We report clinical and haematological data on 54 subjects with Hb Dhofar (37 heterozygotes, 14 homozygotes and three compound heterozygotes with a different β-thalassaemia mutation). In heterozygotes, the level of Hb Dhofar ranged from 8.8% to 21.5%. All heterozygotes had Hb A₂ > 3.5%, consistent with β-thalassaemia trait. Hb Dhofar in homozygotes and compound heterozygotes ranged from 26% to 59.7%, with a peripheral film consistent with homozygous β-thalassaemia. Age at presentation in homozygotes ranged between 6 months and 8 yr, with a majority presenting before 5 yr of age. All had splenomegaly and six (43%) had undergone splenectomy. All had some degree of frontal bossing and in particular, two patients with infrequent transfusions had marked thalassaemic facies and stunting of growth. Hb Dhofar can be mistaken for Hb D as the electrophoretic mobility is similar, but differs from it by a variable and reduced quantity of variant Hb in both heterozygotes and homozygotes. Clinical and haematological data suggest that this mutation behaves like a moderately severe β⁺ thalassaemia allele resulting in a thalassaemia intermedia phenotype.