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Dinucleotide deletion in –α3.7 allele causes a severe form of α+ thalassaemia

Abstract: We describe a family of Italian origin in which the father and his two children had hypochromia and microcytosis with normal iron status. All individuals underwent an uneventful clinical course and required no treatment. To investigate the molecular basis of this phenotype, which is a prerequisite for further genetic counselling, we revealed that all affected family members are carriers of a common form of α+ thalassaemia resulting from the deletion of 3.7 kb of the α‐globin cluster (αα/−α3.7). However, this genotype alone could not account for the phenotype presenting in this family. Further characterization of the α‐globin genes demonstrated an additional AC deletion in the vicinity of the initiation codon of the −α3.7 allele. This secondary mutation causes an additional impaired translation of the affected allele producing increased globin chain imbalance. This leads to a more severe phenotype, as heterozygotes for such mutation (αα/−αT) have hypochromic microcytosis and abnormal globin chain synthesis that mimic α0 thalassaemia trait (−−/αα). Accurate genotyping of α globin determinant is absolutely required as there is a possibility that an interaction of this unusual double mutation with other common α0 thalassaemias (−−/−αT) can give rise to a very severe, probably fatal, α thalassaemia.