Globally, the frequency of alpha-thalassemia is low, but in some tropical and subtropical areas the frequency of carriers could be high (80-90%). However, the disease is unexplored in Sudanese, mainly because of the limited accessibility to molecular diagnostic facilities in the country. (10,11,12,13) In this study we report that at least 7% of hypochromic microcytic anaemia patients were carriers of -a3.7 deletion. Since incidence and prevalence of this syndrome was not well described in local population, it is extremely likely that a-thalassaemia triat may have been confused with iron deficiency state, especially if it was not assessed. (14,15,16,17)
The RBCs in adult carriers showed a significant increase in counting with significant association with the mutation “P-value <0.05”, while in the children they were normal in count. The increase of RBCs count can be considered as a matter of compensation, a finding that have been reported before. (18,19,20) The haemoglobin concentration revealed mild anaemia in adults and children. This was previously reported (14), where alpha thalassemia trait patients were characterized by slight reduction in haemoglobin level. The MCV and MCH showed microcytosis and hypochromasia in adults, and this finding is consistent with many previous studies concerning the contribution of alpha thalassemia to microcytosis and hypochromia (20,22,23,24,25,26,27,28), while others (14,21) reported slight microcytosis and hypochromasia or sometimes normal with alpha thalassemia trait. Unlike many other similar studies that have examined the red cell indices in alpha thalassaemia, present cohort showed significantly lower MCV (52-53fL) giving an impression of additional pathology. The marked reduced MCV in the adult group, irrespective of their alpha thalassaemia carrier status, could be caused by the effect of coincidental chronic infection leading to anaemia of chronic disease.
The severe microcytosis and hypochromasia that is reported here might also be due to a coinheritance of the α3.7 allele with other deletion type or point mutation, such as AC deletion in vicinity of the initiation codon of the – α3.7 allele. (29) RDW_CV of the -α3.7 heterozygous group revealed anisopoikilocytosis, in adult males and females, while in children showed mild anisopoikilocytosis, this finding is consistent with previous studies. (28,30,31)
The observed absence of –a4.2 deletion in this study does not completely rule out the presence of a+ thalassaemia in the general population as this study only focused on hypochromic microcytic anaemia patients. Since heterozygous a+ thalassaemia may have a completely normal blood count or trivial hypochromia and anaemia, more inclusive study is required to confirm the observation.
In conclusion we confirm the presence of α3.7 allele in Sudanese with marked microcytosis and hypochromasia, where the disease was unknown before. This suggests that, previous migration from West Africa crossing Sudan was the main cause of transmission of such type of mutation in Sudanese.