Fortuitous description of haemoglobin A2' [δ16 (A13) Gly→Arg (GGC→CGC)] in a Tunisian family: study of the molecular defect and its origin.

The most common inherited haemoglobin disorders encountered in Tunisia are β-thalassemia and sickle cell disease, which result from mutations in the β-globin gene. Few studies focused on δ-globin gene variations responsible for δ-thalassemia or HbA2 variants. HbA2' [δ16 (A13) Gly→Arg (GGC→CGC)] is a δ-chain variant that has been identified in several populations of African origin. We report herein for the first time the description of HbA2' in the Tunisian population. Identification of HbA2' in the studied family was carried out by high-performance liquid chromatography and confirmed by sequencing analyses of the whole δ-globin gene. Haplotypes of the β-globin gene cluster were constructed by mapping the restriction sites using polymerase chain reaction followed by enzymatic digestion. Compound heterozygosity of HbA2' with HbO-Arab was identified in the proband. The mother and two other siblings showed heterozygous HbA2' whereas the father showed heterozygous HbO-Arab. The sum of HbA2 and HbA2' in all cases was less than 4%, thus excluding β-thalassemia. β-cluster haplotype analysis revealed that this mutation was associated with the F haplotype (-+--+++). The unique origin of this mutation in Africa is likely since the linked β-cluster haplotype is one of the major haplotypes found in African populations.